AGCO Automotive Vehicle Questions Page

AGCO Automotive Vehicle Questions
Air Condition/Heating
QUESTIONS
  1. A few months ago, the blower on my car air conditioner quit working. The blower control module was replaced and it worked for two months. It quit again and the problem was again the blower control module. Now the module has failed again.
  2. After driving a while my air conditioner stops cooling. If I turn it off it will cool again after a while. I checked and the compressor is still turning when it stops cooling and the system is properly charged.
  3. After having the compressor replaced on my GM SUV, the rear unit cools well but the front is not as cool as it needs to be, any ideas?
  4. After replacing the battery, my air conditioner and heater controls no longer work. All air seems to blow from the defrost regardless of selector position?
  5. After replacing the compressor on my air conditioner the system seems to be over charged, not cooling and pressure too high. We added the exact amount called for, how can this be?
  6. An air conditioner hose has started to leak at a crimped fitting. Can these connections be repaired?
  7. An overcharged air conditioner has what symptoms?
  8. Can a worn serpentine belt cause my air conditioner to stop working at times?
  9. Could a dirty cabin filter cause the evaporator to freeze up on my vehicle air conditioner?
  10. How could a bad catalytic converter cause my air conditioner to stop cooling?
  11. How could an air conditioner get over charged?
  12. How does an automobile air conditioner clutch work?
  13. How does an expansion valve work in an air conditioning system?
  14. How does and air conditioner produce cold air?
  15. How does drawing a vacuum on an air conditioner help remove moisture from the system?
  16. How long does water normally drip from the air conditioner in a vehicle once turned off?
  17. I have a Jeep Cherokee with a very musty odor that comes from the air conditioner vents. Is there anything that can be done?
  18. I have a strange problem. At idle my air conditioner cools okay. If I speed up the engine or start driving, the temperature warms up. Any ideas?
  19. I have been told it is not proper to simply add refrigerant to an A/C system that is low?
  20. I have estimates to replace a leaking hose on my air conditioning system. One is higher than the others, and includes a receiver/dryer assembly that the less expensive quotes don’t. Should the receiver/dryer be replaced?
  21. I recently bought a vehicle and notice when sitting at an idle the air conditioning does not cool well.
  22. I replaced the AC compressor on my vehicle, how much oil should I add to the system?
  23. If my cabin filter was plugged what would the symptoms be?
  24. Is an electronic leak detector better than dye for finding air conditioner leaks?
  25. Is it easier on my air conditioner to turn it off of maximum position when it is very hot?
  26. Is there a problem with adding sealer to my vehicle air conditioner?
  27. My air conditioner blows hot air. I had it checked and the shop says the system is working. How could it blow hot if it is working?
  28. My air conditioner compressor has become noisy, but the system still cools okay. One mechanic says waiting until it breaks and another suggest changing it now. What is your opinion?
  29. My air conditioner does not blow as hard as before?
  30. My air conditioner drips water under my car. Where does the water come from?
  31. My air conditioner stopped working and the shop refused to work on it. They said the system was contaminated, what can I do?
  32. My air conditioner stops cooling after driving for a while
  33. My air conditioner will blow fine on high but no air comes out at any other speed. Any ideas?
  34. My older vehicle needs air conditioner repair. With the price of R12 should I consider converting to R134A to save expense?
  35. My vehicle air conditioner stops cooling when I sit at an idle but cools driving down the road.
  36. My vehicle blows cool on the right side and warm on the left.
  37. Occasionally, when my AC is on and I accelerate, there is a loud squeal that occurs. This never happens with the AC off.
  38. Recently a shop suggested that I have my air conditioner dryer replaced, evacuated and recharged as a preventive maintenance. Can this extend the life of the unit?
  39. Should I turn off my air conditioner when starting my vehicle to lessen the load on my battery?
  40. The air conditioner blower (fan motor) on my Honda is noisy on high. Will it hurt anything to not change it immediately?
  41. The air conditioner clutch has gone out on my vehicle. The mechanic wants to change the compressor and clutch, is this best?
  42. The air conditioner in my Toyota does not cool as well as it used to. I have been told it is not proper to just top it off like I used to do. Can you explain why this is no longer acceptable?
  43. The blower control module in my vehicle has been replaced twice. Why would it keep failing?
  44. The clutch on my air conditioner is making noise. Can it be replaced separately or must I replace the entire compressor?
  45. The compressor on my air conditioner is bad and I have received widely ranging price quotes, what should this job cost?
  46. The compressor on my vehicle locked up. The shop that checked it said I should replace the condenser as well as the dryer, expansion valve and compressor. Why should the condenser be replaced if it is not leaking?
  47. The heater in my vehicle blows only cool air regardless of the dial setting.
  48. The high-side pressure on my air conditioner is too high and the system does not cool well. What things could cause this?
  49. There is a leak in my air conditioner that I cannot find. About once a year it quits working and must be charged. Dye was added to the system but does not show up.
  50. There is a slow leak in my air conditioner and have been told sealer can be added to repair this. Is this a good idea?
  51. Three compressors were replaced on my vehicle in the last three years. They work okay for a while and then start to leak at the seal between the halves of the case. Are these all defective are is something causing this?
  52. What are the benefits of vacuuming an air conditioning system before charging?
  53. What are the common causes of a serpentine belt burning on the drive pulley?
  54. What are the symptoms of a bad air conditioner clutch?
  55. What are the symptoms of a bad evaporator core?
  56. What are the symptoms of a dirty evaporator core?
  57. What are the symptoms of a plugged cabin filter?
  58. What are the symptoms of an over charged AC system?
  59. What are the warning signs of an air conditioner compressor failing?
  60. What can I do to extend the life of my vehicle’s air conditioning system?
  61. What is a cabin filter?
  62. What would a greenish liquid leaking from the air conditioner (AC) condenser of my vehicle be?
  63. When adjusting the inside temperature of my car, there is a popping noise under the dash.
  64. When driving, my air conditioner cools fine. When I sit idling the vehicle warms up.
  65. When my air conditioner gets too cold I sometimes turn the heater on slightly. A friend said this could damage my air conditioner.
  66. When my vehicle sits at a stop light or is not moving the air conditioner quits cooling. When diving 45 MPH it cools fine.
  67. When starting my vehicle, should I switch off my air conditioner, to reduce the strain on the starter?
  68. Why do air condition systems today seem to leak more than in the past?
  69. Why do automobile air conditioners fail?
  70. Why does my air conditioner cause water to drip under my car?
  71. Why does my engine bog down when I turn on my defrost?
  72. Why would an orifice tube keep clogging up on an air conditioning system?
  73. Why would the air conditioner on my vehicle stop blowing out of the vents and start blowing defrost when I accelerate my vehicle?
  74. Why would the blower motor resistor keep failing on my vehicle?
  75. Why would the clutch on my air conditioner fail?
ANSWERS
  1. A few months ago, the blower on my car air conditioner quit working. The blower control module was replaced and it worked for two months. It quit again and the problem was again the blower control module. Now the module has failed again.

    Blower control module failure can often be traced to excess current draw from the blower motor. As blower motors age, the current [in amps] required to turn them can increase. The excess amperage will destroy control modules and can burn wiring. Replacing the blower module is treating the symptom. The circuit should be tested for amperage draw and proper grounding. If amperage is too high, the motor or connection causing the problem should be replaced.
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  2. After driving a while my air conditioner stops cooling. If I turn it off it will cool again after a while. I checked and the compressor is still turning when it stops cooling and the system is properly charged.

    If the compressor is still turning and the system is properly charged, the most likely problem is the evaporator freezing. If the system has a cycle switch, I would first check that. Many AC compressors today do not have cycle switches and instead are variable displacement. They run all the time and vary compressor displacement to vary cooling. Adjustments are made based on the low side pressure. In such a system, if the compressor fails, it may not cut back and the system will freeze. Once the evaporator freezes, the system will stop blowing cool air, until it is allowed to thaw.
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  3. After having the compressor replaced on my GM SUV, the rear unit cools well but the front is not as cool as it needs to be, any ideas?

    If the system was working normally before the compressor failed, likely the problem is relating to refrigerant flow. GM uses an expansion valve to control the rear evaporator and an orifice tube to control the front. When compressors fail, there is often debris that enters the system. This debris can cause the expansion valve to malfunction. One possibility is this is causing unregulated flow to the rear core and inadequate cooling on the front.
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  4. After replacing the battery, my air conditioner and heater controls no longer work. All air seems to blow from the defrost regardless of selector position?

    On older vehicles with vacuum controlled mode doors, I would suspect a vacuum line may have been pulled off or broken when the battery was replaced. On newer vehicles with electronic actuators, disconnecting the battery can sometimes cause them to lose their memory of actuator position. When this happens the system may default to defrost. Make sure the ignition is off and disconnect the battery again, for several minutes. After reconnecting the battery, turn the ignition switch on, without starting the engine and wait for at least five minutes. If that does not reset the system, it can sometimes still be corrected by a scan tool, with body control reset capability.

    Please see our Detailed Topic Heaters and AC Systems for more information.


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  5. After replacing the compressor on my air conditioner the system seems to be over charged, not cooling and pressure too high. We added the exact amount called for, how can this be?

    Too much oil in the system will displace the refrigerant and cause an overcharge even with the proper amount of refrigerant. This sometimes occurs when oil is added with the new compressor and the system already has the proper amount.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  6. An air conditioner hose has started to leak at a crimped fitting. Can these connections be repaired?

    Crimped fittings do not just become loose, the rubber in the hose is likely deteriorating. This can be a symptom of a contaminated system, and should be fully diagnosed and repaired before additional damage occurs.
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  7. An overcharged air conditioner has what symptoms?

    The leading symptom will be inefficient cooling, though the system may continue to cool. The result will always be elevated head pressure and normally very rapid damage to the compressor.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  8. Can a worn serpentine belt cause my air conditioner to stop working at times?

    Yes, a worn belt can slip slightly and generate heat. There may be no noise or other outward symptom of slipping. The heat generated by the slipping belt over-heats the air conditioner clutch and can cause it to release. This heat may also permanently damage the clutch. Serpentine belts should be inspected with a gauge made for the purpose and not simply visually inspected.

    For more information on belt inspection, please see our Detailed Topic, Symptoms of A Bad Serpentine Belt and EPDM Belts.


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  9. Could a dirty cabin filter cause the evaporator to freeze up on my vehicle air conditioner?

    Lack of air flow caused by a restricted cabin filter can cause the evaporator to freeze as well as other problems. Lack of air flow can also contribute to refrigerant not fully evaporating to gaseous form. If refrigerant leaves the evaporator in the liquid state, it can cause compressor damage.
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  10. How could a bad catalytic converter cause my air conditioner to stop cooling?

    A plugged catalytic converter could cause the engine to overheat and the air conditioner may be shut off as a result. Another way might be if the bad converter reduced idle speed. Many vehicles shut off the air conditioner if idle speed falls below specifications.

    For more information on catalytic converters, please see our Detailed Topic, Catalytic Converters Problems.


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  11. How could an air conditioner get over charged?

    The leading cause is improper service; Trying to charge the system by watching gauges, rather than evacuating and adding a measured content. As little as two ounce can cause a major problem on some systems.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  12. How does an automobile air conditioner clutch work?

    Most air conditioner clutches have three primary components. The hub, drive-plate and magnetic coil. The hub mounts to the compressor with a bearing. Being mounted on a bearing allows the hub to turn freely, driven by a belt. Inside of the hub is the magnetic coil. When air conditioning is desired an electrical current energizes the coil. This pulls the drive-plate firmly against the hub. The drive-plate is anchored to the compressor shaft so once the coil is energized, the drive-plate and compressor shaft are turned by the hub and belt.

    Magnetic automotive air condition compressor clutch.  Please click image for larger view

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  13. How does an expansion valve work in an air conditioning system?

    Air conditioning functions by converting a high pressure, liquid refrigerant to a low pressure gas. This is accomplished by restricting the flow of the high pressure liquid. As flow is restricted, pressure drops, the liquid flashes to a gas and absorbs heat [energy] in the process.

    An expansion valve is a temperature/pressure controlled device to accomplish the pressure drop. As the temperature and pressure approach freezing, the expansion valve can close and limit the refrigerant flow. This has the advantage of keeping the evaporator as cold as possible while preventing freezing. If the evaporator core were allowed to freeze, cooling would be diminished. The expansion valve maximizes cooling by keep the evaporator core at the optimal temperature.

    Typical air conditioner expansion valve

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  14. How does and air conditioner produce cold air?

    Air conditioning works by removing heat. Since the absence of heat is cold, this is what we experience. The process works because when matter changes state (e.g., liquid to gas, solid to liquid) energy is absorbed or released.

    The refrigerant in the system enters the compressor as a low pressure gas. The compressor raises the pressure and makes it a high pressure gas. This high pressure gas is forced through a condenser, where it changes state to a high pressure liquid. In changing state, energy is released. This is the heat we feel being blown away by the fan, outside of the vehicle.

    The liquid now travels to a restriction, built into the system. Flowing through the restriction the pressure is greatly lowered. As the pressure drops, the liquid changes state to a gas. This change of state absorbs energy in the form of heat from the vehicle interior. Removing this heat results in cooling the vehicle. The low pressure gas now returns to the compressor and the cycle begins again.

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  15. How does drawing a vacuum on an air conditioner help remove moisture from the system?

    Water boils at 212 degrees Fahrenheit, in the atmosphere and at sea level. As pressure drops, so does the boil point. Reducing pressure to 29 inches of vacuum, causes water to boil at 76.6 degrees Fahrenheit. As the moisture in the air conditioner boils it turns to vapor, which is drawn out with the vacuum pump.

    For more information, please see our Detailed Topic How Automotive Air Conditioning Works.


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  16. How long does water normally drip from the air conditioner in a vehicle once turned off?

    Water dripping under a vehicle is from condensation of the humidity removed and should stop in less than a minute of shutting the vehicle off. Continued dripping is often a sign of an evaporator that is freezing, a leaking heater core or a restriction in the drain.
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  17. I have a Jeep Cherokee with a very musty odor that comes from the air conditioner vents. Is there anything that can be done?

    Depending on the severity of the problem there are several approaches. First with the vehicle doors open and the air conditioner on high, place the dash selector to the fresh air setting. Select a disinfectant in a spray and spray the mist into the fresh air intake at the base of the windshield. While continuing to spray have some one turn the vehicle off and let it sit for several hours. In minor cases this gives good results.

    In other cases it may be necessary to remove the blower resistor and/or fan motor and spray the evaporator core with a professional strength product. This is best done by a professional as these chemicals can be highly toxic.

    In more severe cases removal of the dash, evaporator core and replacement of the insulating film around it are necessary. This also involves complete cleaning and disinfecting of the core and all duct work. Recharging of the air conditioning system would also be needed so this usually falls into the realm of professional service.

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  18. I have a strange problem. At idle my air conditioner cools okay. If I speed up the engine or start driving, the temperature warms up. Any ideas?

    Reduced cooling at higher engine speed often means there is a restriction in the system. If there are no kinked or smashed hoses or lines, there will normally be a plugged component. Common problem areas are the orifice tube, if so equipped or the expansion valve if not. Plugging of components is normally a symptom and points to a larger issue, the source of the material that caused the blockage. Very often this is going to indicate a failing compressor or a ruptured descant in the accumulator.
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  19. I have been told it is not proper to simply add refrigerant to an A/C system that is low?

    This is correct, it is harmful simply to add refrigerant. There is no way to judge whether the proper charge is in the system, other than to evacuate, and add the proper charge with a charging cylinder. Gauges are far too unreliable and may result in dangerous over or under charging.

    With smaller systems, charge quantity is more critical. Most systems hold 32 ounces or less, some as little as 12 ounces. One ounce, on such a small system, results in a 10% error and damage to the system. Overcharge can damage the compressor, coils and ruin seals. Under-charge may not transport oil, resulting in a burned up system.

    There is no way to determine air content, nor the amount of oil in the system without evacuation. Small leaks can cause the system to lose oil. Adding refrigerant, without replacing the exact amount of oil we lose, can damage the system. The only way properly to charge the system is completely removing the contents and replace the specified amounts of refrigerant and oil.

    See our Detailed Topic article Preventing Air Conditioner Failure for far more details.

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  20. I have estimates to replace a leaking hose on my air conditioning system. One is higher than the others, and includes a receiver/dryer assembly that the less expensive quotes don’t. Should the receiver/dryer be replaced?

    The receiver/dryer should be replaced any time the system is opened. It contains a desiccant that removes moisture from the system and is the number one line of defense for the system. This looks like another example of more is less. Doing the job properly the first time is the least expensive route.
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  21. I recently bought a vehicle and notice when sitting at an idle the air conditioning does not cool well.

    Lack of cooling at low speed is a common symptom of several problems. When the engine slows (at idle) the AC compressor also slows. This lowers pressures in the system and makes almost any problem more noticeable. An additional factor is AC systems do not produce cold, they remove heat. This heat is given off at the condenser. Sitting still there is far less air moment to dissipate this heat.

    A weak compressor, a leak in the system, an over-charged system, a radiator cooling fan not working and several other things will all have this same symptom. The only way to know would be to run a diagnostic check of the system. I would advise doing this ASAP as far more damage normally results, quickly.

    See our Detailed Topic article Preventing Air Conditioner Failure for far more details.

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  22. I replaced the AC compressor on my vehicle, how much oil should I add to the system?

    Adding oil to an AC system is a bit tricky. Oil circulates with the refrigerant and settles in different components at different times. It is difficult to know exactly how much oil is already in the system and exactly where it is located. The safest bet, if the system has not been previously serviced, is to drain the removed component, measure what comes out and add that amount. If oil has been removed or added previously, draining every component and adding the specified amount may be the only answer. Too much oil takes the place of refrigerant and will result in an overcharge of the system when the proper amount of refrigerant is added.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  23. If my cabin filter was plugged what would the symptoms be?

    Symptoms of a plugged cabin filter will vary based on the design of the vehicle. In some cases there may be almost no symptoms at all. This is because some systems allow a plugged filter to be bypassed with unfiltered air. On other vehicles the airflow from the vents may be greatly diminished. In other cases the evaporator core could freeze and quit cooling after driving a distance. The worse issue may be the possibility of refrigerant not flashing completely and being returned as a liquid to the compressor. In some cases the excessive amperage caused by the fan pulling through a restricted filter can burn up connectors and control panels.
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  24. Is an electronic leak detector better than dye for finding air conditioner leaks?

    One is not better than the other, they are complementary technologies. Better shops often use combinations of various electronic and ultrasonic leak detectors as well as dye and even bubble test. Each has a place and each is effective at certain type leaks.
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  25. Is it easier on my air conditioner to turn it off of maximum position when it is very hot?

    Actually the maximum position may be easier on the unit than the normal position. Many units pull in fresh air in the normal mode. This hot and humid air has to be cooled, which may increase the load in normal mode. In maximum mode, most units recycle the already cooled air, which may lower the load on the system.
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  26. Is there a problem with adding sealer to my vehicle air conditioner?

    Sealers can cause all sorts of problems in air conditioner systems. Some sealers and stop leak products function by swelling seals, which virtually destroys the rubber. Others harden when exposed to air. Perhaps worse, refrigerant contaminated with sealer can no longer be recycled. Since it is against Federal law to release refrigerant into the atmosphere. Because of the costs and liability of disposing of contaminated waste, many shops may refuse to work on the system. The vehicle owner will ultimately pay the costs, if the system is repaired.

    For more information on contaminated refrigerant, please see our Detailed Topic on the subject.


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  27. My air conditioner blows hot air. I had it checked and the shop says the system is working. How could it blow hot if it is working?

    Most modern systems are re-heat style. This means the air is first cooled and then heated to adjust the temperature. Diagnosis requires an understanding of the entire system as opposed to simply checking the air conditioning. The benefit is dehumidifying the air and infinite temperature control.

    The disadvantage is the complexity required. There are a series of ducts and doors, normally controlled by servo motors. These in turn are controlled by the control panel. A malfunction in the system may result in air being heated more than desired even though the air conditioner itself is functioning as designed.

    See our Detailed Topic Heaters and AC Systems for more information.

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  28. My air conditioner compressor has become noisy, but the system still cools okay. One mechanic says waiting until it breaks and another suggest changing it now. What is your opinion?

    If the compressor fails and comes apart, debris will be spread throughout the system. This is nearly impossible to clean perfectly. Any debris that remains can drastically shorten the life of the new compressor. The system will have to be repaired when it fails. The chances of a lasting repair are much better before complete failure. The cost may also be less now, because the need for extensive disassembly and cleaning would be less likely.
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  29. My air conditioner does not blow as hard as before?

    If air volume is lower than normal on all fan settings, suspect a restriction in the system. If the vehicle is equipped with a “cabin” or HVAC filter, check and replace if needed.

    Another common restriction is small plastic shopping bags that are drawn into the system from outside. Driving in parking lots, these bags are often pulled into the air intake, blocking the air flow.

    The evaporator core can also become restricted. This is common on vehicles without “cabin” air filters. A professional cleaning may be necessary if this is the case. Evaporators are very easily damaged and normally quite expensive to replace.

    A malfunctioning mode or blend door, in the duct work can also cause lack of air flow. These doors open and close to duct air through the system. They are operated by servo motors and sometimes vacuum controls. When they malfunction air flow may be blocked.

    See our Detailed Topic Heaters and AC Systems for more information.

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  30. My air conditioner drips water under my car. Where does the water come from?

    Air conditioning not only removes heat, but also removes humidity from the air in the vehicle. Lower humidity makes the temperature much more comfortable. The humidity in the form of water, collects on the evaporator core. As it drips off the core, a tray catches the water and directs it outside the vehicle, where you see it dripping.
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  31. My air conditioner stopped working and the shop refused to work on it. They said the system was contaminated, what can I do?

    Adding chemicals to an air conditioner, such as sealer and some off-brand refrigerants may contaminate the system. Federal law states that refrigerant should be recycled. Shops use an electronic identifier to test content before recycling. Recycling is usually impossible with a contaminated refrigerant. The contents will have to be removed, with a machine dedicated for the purpose. The waste may then have to be identified by a lab, before a processor with accept it. Normally waste is transported to a facility and destroyed. The considerable cost is charged back to the vehicle owner. A contaminated air conditioner may be considered not practical to repair, due to the expense of removing and destroying the contaminants.

    For more information on contaminated refrigerant, please see our Detailed Topic on the subject.


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  32. My air conditioner stops cooling after driving for a while

    Two of the leading causes for lack of cooling, after driving for a distance, are the system freezing up and the compressor clutch overheating. Several things can cause either. Lack of air flow, such as a restricted cabin filter can cause the evaporator to freeze. Low charge, a sticking expansion valve and moisture in the system, are other possible causes.

    The compressor clutch may overheat and not engage. This will keep the compressor from turning and stop cooling. The drive-plate (see How does an automobile air conditioner clutch work) can wear, increasing the gap between itself and the hub. When this happens it will slip. The slippage creates heat and the coil will release. Once the clutch cools, it may begin working again.

    Normally with freeze up, there will be a lot of water dripping under the vehicle, after the unit is turned off. With a bad clutch, there will be little or no dripping.

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  33. My air conditioner will blow fine on high but no air comes out at any other speed. Any ideas?

    Most air conditioner blower speeds are controlled by a module or a resistor unit. On high speed, the system often bypasses this component and runs full voltage to the blower motor. If the module or resistor unit fails, the fan will not blow on any speed except high. Failure of these units is also often accompanied by burned connections in the wiring. The root cause is excessive amperage being drawn by the blower motor. The amount of amperage being drawn should be checked before replacing the module or resistor unit.
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  34. My older vehicle needs air conditioner repair. With the price of R12 should I consider converting to R134A to save expense?

    At AGCO we do not convert air conditioning systems from one refrigerant to the other. Rather we repair R12 systems with R12. The condenser and hoses on an R12 system are different than those on a system designed for 134A.

    Even with the price of R12, the refrigerant in a system is only a small part of the cost of repair. In a very large system the cost difference is usually less than $120.00. In most systems it is considerably less. This small savings can be quickly eroded by an air conditioner that does not cool as well as before. Worse is a system that loses refrigerant or has to be redone.

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  35. My vehicle air conditioner stops cooling when I sit at an idle but cools driving down the road.

    Some of the more common causes include, a weak or non-functioning A/C condenser fan. Without a fan to move air through the condenser, pressure will rise and the compressor may be shut off. Driving provides air flow without the need for the fan.

    Another cause is a weak compressor. A weak compressor may produce adequate pressure while the engine is running at speed but not enough at an idle. A vehicle low on charge can also show similar symptoms. Finally, an engine idling too low may cause the compressor to shut off. A dirty throttle body sometimes causes this condition.

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  36. My vehicle blows cool on the right side and warm on the left.

    In systems with dual zone temperature control, this can indicate a failed blend door or servo. Other causes can include a bad automatic temperature control head and being low on refrigerant. Since the evaporator core is almost always on the right, a low system can sometimes cool the right and not the left.

    For much more information, please also see our category on air conditioner service.

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  37. Occasionally, when my AC is on and I accelerate, there is a loud squeal that occurs. This never happens with the AC off.

    A bad or loose belt is a possible cause. Check the belt and the tension device. If they are good, liquid returning to the compressor can cause such a noise. Liquid cannot be compressed and the compressor temporarily locks up, causing the belt/clutch to squeal loudly. Tremendous damage can be done to the system. A few possible reasons for this problem include.

    • The system is over charged, too much refrigerant has been added.

    • Too much oil has been added to the system

    • Insufficient air flow across the evaporator. This can result from a dirty cabin filter, dirt in the evaporator, a bad blower motor, a restricted air duct, etc.

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  38. Recently a shop suggested that I have my air conditioner dryer replaced, evacuated and recharged as a preventive maintenance. Can this extend the life of the unit?

    This procedure is not in any manufacturer’s recommendations that I am aware of. With their current trend toward reducing maintenance it is not likely to appear in the future. But then, they have a vested interest in vehicles not lasting too long.

    That being said, I cannot see any harm as long as the job is properly performed. One problem might be in a cost/benefit analysis. A good deal of research would need to be done to justify the cost and I am aware of no such research. With no prior knowledge you would be guided by theory alone, but the potential for savings is possible.

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  39. Should I turn off my air conditioner when starting my vehicle to lessen the load on my battery?

    Modern vehicles control the air conditioner through the body control module (BCM). It is not necessary to turn the unit off when starting as the BCM will do this automatically.
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  40. The air conditioner blower (fan motor) on my Honda is noisy on high. Will it hurt anything to not change it immediately?

    Noise is one indication of a failing or restricted motor. A good fan motor normally draws around eight to ten AMPS. Much more is a problem and will burn out the transistor that controls the speeds and possibly damage the wiring harness. With a bad or restricted motor, this may occur. Replacement should be as soon as possible.

    We also find cases of leaves and debris that get into the blower and make noise. This is an easy problem to correct. You might pull the motor and see if there is any debris in the fan. If not I would replace the motor, as soon as possible.

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  41. The air conditioner clutch has gone out on my vehicle. The mechanic wants to change the compressor and clutch, is this best?

    The clutch and compressor have gone through the exact same number of cycles. If the clutch has failed the compressor will likely not be far behind. A quality clutch assembly cost nearly as much as a new compressor with a clutch and the time to replace is nearly equal. I agree with your mechanic, I would suggest replacing both.
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  42. The air conditioner in my Toyota does not cool as well as it used to. I have been told it is not proper to just top it off like I used to do. Can you explain why this is no longer acceptable?

    The practice of “just adding a little Freon,” was never a proper procedure. With R134A refrigerant the results can be catastrophic. Systems are much smaller than they used to be and the volume of charge is much more critical.

    Reading the pressure, as with an older system is not accurate with the very small system of today. A slight under-charge can result in the compressor not being lubricated and a slight over-charge can damage the system, from excess pressure. The best way to service the system is to evacuate fully. Then the exact amount specified can be added with a charging cylinder.

    See our Detailed Topic article Preventing Air Conditioner Failure for far more details.

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  43. The blower control module in my vehicle has been replaced twice. Why would it keep failing?

    Blower control modules are often ruined because the blower motor pulls too much amperage through them. Tell-tale signs are connectors that are melted, discolored and burned wires. The blower motor should be checked for excessive current draw. A restricted blower air intake, for instance from a clogged cabin filter, can also cause the motor to draw excessive amperage.
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  44. The clutch on my air conditioner is making noise. Can it be replaced separately or must I replace the entire compressor?

    The answer depends on the vehicle and how many miles it has. On some vehicles, a new compressor with a clutch is not much more than the cost of the clutch alone. If the vehicle has high-mileage it may be as wise to replace the entire compressor, which may fail in the future.

    The best course is to ask for an estimate both ways and decide based on the price difference and how long you plan to keep your vehicle. At AGCO we normally present an estimate both ways with a recommendation based on experience with the vehicle.

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  45. The compressor on my air conditioner is bad and I have received widely ranging price quotes, what should this job cost?

    It would be impossible to quote a price without knowing the problems in the system. Price could vary greatly for many reasons. The most important thing to remember is why did the compressor fail.

    If you have read our philosophy on lowest price verses lowest cost, you will know we believe that a high quality repair is much less expensive than a cheaper temporary repair.

    For example compressor failure can be due to high system pressure. This can be due to cooling fans not working properly. Failure to diagnose the cooling fans may result in a lower estimate of repair, but can also result in the compressor failing again.

    Other price differences could be due to a rebuilt compressor being used rather than a new one. Rebuilt compressors rarely give equal service to new. Other factors include flushing the system of contaminants, replacing the filter/dryer and sometimes the condenser.

    All these factors and others, will drastically affect price. They also drastically affect performance and life of the system.

    I feel it is always less expensive to diagnose properly and repair the system fully, even though the initial price may be more expensive.

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  46. The compressor on my vehicle locked up. The shop that checked it said I should replace the condenser as well as the dryer, expansion valve and compressor. Why should the condenser be replaced if it is not leaking?

    The condenser on a R134A system has many, many feet of tubing, with very small passages. When a compressor seizes up, there is normally a great deal of metal particles that enter the system. These particles are often lodged in the tiny condenser passages. There is no way effectively to clean such a condenser. Should a particle become dislodged later and go through the new compressor, damage will occur. With a metal contaminated system, condenser replacement is a wise step.

    The image below shows an actual section of condenser tubing and how small the tube openings are. In a serpentine design condenser, these tubes wind back and forth and are very long.

    relative size of openings in AC condenser tube.  Click image for a larger view

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  47. The heater in my vehicle blows only cool air regardless of the dial setting.

    If the vehicle has a temperature gauge make sure the engine is getting to operating temperature. If there is no gauge, temperature can be checked with a thermometer. If the engine is warm enough, normally 195 degrees Fahrenheit or more, flow should be checked. By checking the inlet and outlet temperature on the heater hoses, it can be determined if the hot water is flowing through the heater core.

    If flow is present and adequate, there is likely a problem with the blend door in the heater case. The blend door ducts air through the core when heat is desired and around it when not. If the door does not operate, heat will not enter the passenger compartment.

    Blend doors are controlled by a number of means. Some are cable or vacuum operated, others electrical and many are computer controlled. Diagnosis of computer controlled heating, ventilation and air conditioning (HVAC) systems is quite complex and best left to a properly trained professional.

    If your system is vacuum operated, check to see if the vacuum lines are attached and that there is a source of vacuum to the system. On a cable system turning the knob should move the cable, which should be attached to the door.

    See our Detailed Topic Heaters and AC Systems for more information.

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  48. The high-side pressure on my air conditioner is too high and the system does not cool well. What things could cause this?

    Excess high-side pressure can result from insufficient air flow pass the condenser, restrictions in the lines or an overcharged system. Bad cooling fans and/or clutches as well as control circuits are common faults. Check to see if the fan(s) are running at full speed or as commanded. Another cause is a dirty condenser core. Debris, leaves and dirt may restrict air flow.

    The only way correctly to verify the proper refrigerant charge, is to evacuate the system and add the proper amount. System over-charge will diminish cooling and can quickly destroy the compressor and damage the system.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  49. There is a leak in my air conditioner that I cannot find. About once a year it quits working and must be charged. Dye was added to the system but does not show up.

    Systems today are very small in comparison to just a few years ago. Some systems only hold 16 to 20 ounces. This makes leaks far more critical. Losing just two ounces can shut the system down and a two ounce a year leak can be hard to find. If dye does not show on any of the external components, the evaporator core is a prime suspect. We use a remote camera system to inspect the evaporator and have found several leaks by this method. Placing the wand of an electronic leak detector in the evaporator case may also help reveal such a leak.
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  50. There is a slow leak in my air conditioner and have been told sealer can be added to repair this. Is this a good idea?

    Definitely not a good idea. Sealer normally functions in one of two ways, either it swells seals or it hardens when exposed to air or moisture. The theory is the swollen seal will seal better and the leak is plugged by the hardened material as it leaks out.

    Any sealing from these concoctions will likely be temporary and they can do great harm. If they harden in your system they can be almost impossible to remove. This can cause any attempt at proper repair to fail. Hoses and internal rubber components could also be damaged. Many shops will refuse future repair or insist that every part of the system be replaced.

    A professional will locate and repair the leak properly. This will be much less expensive in the long run and is the only repair that should be considered.

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  51. Three compressors were replaced on my vehicle in the last three years. They work okay for a while and then start to leak at the seal between the halves of the case. Are these all defective are is something causing this?

    It is very unlikely that you would get three compressors with the same problem. Many times, leaks like you describe, are caused by system pressure rising too high and distorting the case of the compressor. This can result from over charging or cooling fans that do not operate properly.

    High side pressure is closely related to temperature. If the condenser gets too hot, the pressure will rise. The fans are designed to help control this and their function should be verified.

    Charging a system improperly can result in the same problem. Charging a system by checking the pressure is not accurate. Pressure varies considerably with ambient temperature. A system charged with such a method, on a cool day, may be vastly overcharged on a hot day.

    Too much oil in the system could also cause an overcharge. The system needs to be completely drained and all oil removed. Refill with the specified amount of oil, evacuate the system and the proper amount of refrigerant should be added.

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  52. What are the benefits of vacuuming an air conditioning system before charging?

    Drawing a vacuum on an air conditioning system draws air, that would otherwise be trapped, out of the system. Air occupies space and does not provide cooling. Air also contains moisture which is detrimental to the system. By drawing a vacuum on the system, much of the air and moisture are removed.

    For more information, please see our Detailed Topic How Automotive Air Conditioning Works.


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  53. What are the common causes of a serpentine belt burning on the drive pulley?

    Serpentine belts getting hot, burning and breaking are sometimes the result of a seized pulley or accessory being driven by the belt. For instance an air conditioner compressor clutch bearing may seize and the belt will start to slip. Slipping generates tremendous heat and will quickly burn the belt. Worn belts may also slip and overheat the accessory items.

    For more information on belts, see our Detailed Topics article, About Serpentine Belts.

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  54. What are the symptoms of a bad air conditioner clutch?

    An air conditioner clutch is actually several parts (see How does an automobile air conditioner clutch work.) The symptoms will depend on the part that fails. When the bearing fails, the first symptom is noise, eventually resulting in the hub seizing. When the hub seizes, the belt will slip, squeal loudly and break.

    A failed magnetic coil will keep the compressor from operating. The first symptom will be a lack of cooling. Coils also fail intermittently. Intermittent failure results in lack of cooling, normally after driving a distance. Other symptoms can include noise and a burning smell.

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  55. What are the symptoms of a bad evaporator core?

    The primary failure on evaporators is a leak, the symptom would be a loss of refrigerant and a loss of cooling. Evaporators may also become restricted externally as well as internally. With an external restriction, reduction of air volume from the vents would be a symptom. With an internal restriction, loss of cooling after driving is the normal complaint.
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  56. What are the symptoms of a dirty evaporator core?

    Dirty is a relative term and so are the symptoms of a dirty evaporator. A small amount of dirt might diminish cooling slightly and/or restrict air flow from the vents. A more severe amount of debris can significantly block air flow. Blocking air flow can result in the evaporator freezing. A frozen evaporator will quit cooling and may inhibit liquid refrigerant from turning to a gas. If refrigerant does not fully convert from liquid to gas, returning liquid will damage the air conditioner compressor.
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  57. What are the symptoms of a plugged cabin filter?

    A decrease in the volume of air coming from the vents is one sign. Another is a noisy blower, one that sounds like it is turning faster than it is. Restricted cabin air filters can also cause blower motors to burn up, by increasing the amperage they draw. In extreme cases temperature control computers can also be damaged by the higher amperage.
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  58. What are the symptoms of an over charged AC system?

    Lack of cooling and short compressor life are the leading signs. Excessive compressor noise may or may not also be a symptom.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge.

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  59. What are the warning signs of an air conditioner compressor failing?

    The two most common symptoms are noise and lack of cooling at idle. When a compressor becomes noisy, failure is imminent. Replacing it before it fails completely can often prevent a great deal of complications. Lack of cooling at idle can also have other causes. A pressure test of the system is the best way to isolate the exact cause.

    Compressors normally fail for reasons other than the compressor itself. Careful diagnosis is needed to prevent recurrence of the problem. See our Detailed Topic article Preventing Air Conditioner Failure for far more details.

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  60. What can I do to extend the life of my vehicle’s air conditioning system?

    Keeping the condenser clean is always a very good idea. Carefully washing dirt and bugs from the condenser can lower the load on the system considerably. Replacing the “cabin” filter if the vehicle is so equipped can also help considerably. Most of these filters need to be replaced about every 15,000 miles.

    Keeping a good drive belt on the compressor is also critical. Old and worn belts can slip and generate tremendous heat which can damage an air conditioner clutch. Also the system should be serviced immediately when a problem is noticed. For instance insufficient cooling can indicate a low charge, which indicates leakage. Continuing to drive with a low charge may shorten the life of the system.

    Lastly a system should never be “topped off.” This is where refrigerant is added to a partially filled system. Rather any leak should be addressed if possible, the system fully evacuated and recharged with the proper amount of refrigerant.

    See our Detailed Topic article Preventing Air Conditioner Failure for far more details.

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  61. What is a cabin filter?

    The cabin filter is very similar to the filter on a home heating and air conditioning system. It filters air flowing to the evaporator and heater core. By removing dust and debris from the air flowing through these cores, the problem of plugging the air passages are greatly reduced. Not all vehicles have a cabin filter. Those that do need to be replaced on a regular basis.
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  62. What would a greenish liquid leaking from the air conditioner (AC) condenser of my vehicle be?

    If the source of the liquid is the AC condenser, it is very likely trace dye that was added to the system. Many manufacturers and service shops add fluorescent dye to air conditioners to aid in leak detection. With a black light and special glasses the area of the leak is very visible. Amounts large enough to be seen with the eye represent a significant leak in the system. Immediate repair of the leak will help control cost, future damage and contamination of the system.
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  63. When adjusting the inside temperature of my car, there is a popping noise under the dash.

    Temperature on modern vehicles are controlled by a series of electrical actuators and doors that they open and close. Most popping noise under the dash relates to these systems. Often the plastic doors will crack at the point where the actuator drives them. This causes the drive to slip and produces a pop or click. Damaged actuators can also make a pop or click noise.

    See our Detailed Topic Heaters and AC Systems for more information.

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  64. When driving, my air conditioner cools fine. When I sit idling the vehicle warms up.

    There are several possibilities. One is a weak compressor. A weak compressor may produce enough output when turned at higher RPM but not at idle. To test, place the vehicle in neutral and slightly raise the RPM with the accelerator. If cooling returns this is a possibility.

    If cooling does not appreciably increase, there could be a problem with the cooling fan(s). In order for the air conditioner to function, it must give off heat at the condenser. Driving at speed produces enough air flow. When sitting at idle fans must move this air. If a fan fails to turn or turns too slowly the air conditioner may not cool or shut down.

    Being low on refrigerant can also cause this problem. This could be tested by evacuating the system and measuring the charge. If the system is low, it indicates a leak, which should be repaired. Another frequent symptom of low charge is a compressor that cycles on and off frequently.

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  65. When my air conditioner gets too cold I sometimes turn the heater on slightly. A friend said this could damage my air conditioner.

    Many vehicles blend heated air with air conditioned air to control passenger compartment temperature. This will not harm the air conditioner.

    See our Detailed Topic Heaters and AC Systems for more information.

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  66. When my vehicle sits at a stop light or is not moving the air conditioner quits cooling. When diving 45 MPH it cools fine.

    This will almost always be one of three problems. If idle is too low, the computer can turn the compressor off. This can be checked by watching the RPM on the vehicle tachometer. Other causes may be the condenser fan is not working fully, or the compressor is weak. When driving 45 MPH the condenser fan is not required, due to natural air flow. If the fan does not work or work at full speed, the vehicle will warm-up when sitting still.

    A weak compressor acts similarly. The compressor will not produce enough pressure differential, at idle. At higher vehicle speed, the RPM increases and the AC may cool. To test for this, try elevating the RPM at idle. Put the vehicle in neutral and accelerate and hold at 2000 RPM, if cooling gets much better, the compressor is likely.

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  67. When starting my vehicle, should I switch off my air conditioner, to reduce the strain on the starter?

    Virtually all modern vehicles control the air conditioner compressor through the power or body control module. Switching it off during cranking is unnecessary as the computer does this automatically.
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  68. Why do air condition systems today seem to leak more than in the past?

    Actually systems today leak less than past units. Hoses and connections are much better today. Systems also hold far less refrigerant. Older systems often held up to 60 ounces of refrigerant. Systems today may hold as little as twelve ounces. A three ounce leak in a 60 ounce system was hardly noticeable. In a twelve ounce system, three ounces represents 25% of the capacity and the system will stop cooling. The effect of losing refrigerant is simply far more critical today.
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  69. Why do automobile air conditioners fail?

    By a wide margin, the two leading causes are leaks and improper service caused by mis-diagnosis. When a leak develops, refrigerant as well as system oil can be lost. This can cause a wide range of other problems, including compressor damage.

    There are several reasons why an air conditioner may stop cooling. Adding refrigerant to a system, rather than diagnosing the problem, results in over charging the system. This will quickly damage other component and not correct the original issue.

    Please see our Detailed Topic entitled wasting thousands on AC repair for more information on system over charge

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  70. Why does my air conditioner cause water to drip under my car?

    Air conditioning makes the passenger compartment comfortable by removing heat and humidity. The humidity that is removed from the air is seen as water that drips under the vehicle.
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  71. Why does my engine bog down when I turn on my defrost?

    Engine speed is controlled by a component called an idle air control or IAC servo. When the defrost is selected, the air conditioner is turned on. The dehumidified air helps to defrost the windows. The load change from the air conditioner causes the engine to slow down. When operating properly, the idle air control or IAC servo will correct the idle speed, almost immediately. When the IAC sticks or works slowly, there may be a noticeable change in speed when engine load changes.

    For more information, please see our Detailed Topic Idle control and electronic throttle control.


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  72. Why would an orifice tube keep clogging up on an air conditioning system?

    Unless sealer has been added to the system, three things often cause contamination in an air-conditioning system.

    1. Metal, usually from a bad compressor.


    2. Burned oil, also from a bad compressor.


    3. A ruptured receiver/dryer

    If a sealer has been added to the system, the refrigerant may no longer be able to be recycled. The expense of removal and disposal may be excessive. Contaminated systems are always extremely difficult to correct. Sometimes, replacement of every component is the only remedy, and this is on top of the costs of waste disposal.

    For more information on contaminated refrigerant, please see our Detailed Topic on the subject.


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  73. Why would the air conditioner on my vehicle stop blowing out of the vents and start blowing defrost when I accelerate my vehicle?

    Many times the mode door, that controls blower position is vacuum operated. When you accelerate, engine vacuum drops and spring pressure returns the mode door to the default, which is defrost. There is a vacuum accumulator that stores vacuum to prevent this. Chances are the line between the vacuum source and the mode door actuator is leaking. The most common places for leaks are at the engine firewall and under the battery.
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  74. Why would the blower motor resistor keep failing on my vehicle?

    Resistor failure is almost always the result of excessive amperage being drawn through it. The leading source of excess amperage would be a bad blower motor or a motor that is restricted. Poor or loose wiring connections can also increase amperage in a circuit. An ammeter can test motor-draw and a voltage-drop or resistance test can check bad connections.
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  75. Why would the clutch on my air conditioner fail?

    An air conditioner clutch is mechanical and electrical and is prone to wear and tear. They normally last 100,000 miles or more, under normal conditions. Low charge in the system, caused by a leak, may produce over-cycling and quickly wear the clutch. Over-charge, from improper service can also destroy the clutch and compressor very quickly. A dirty condenser will cause excess pressure as will an inoperative condenser fan. Worn drive belts may also drastically shorten compressor clutch life.

    For more information on belt inspection, please see our Detailed Topic, Symptoms of A Bad Serpentine Belt and EPDM Belts.


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