Thursday, October 30, 2014 Detailed Auto Topics
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Every year well-intentioned folks try to recharge their vehicle’s air conditioner. At best they get temporary results and often they get a huge and very costly surprise. With modern air conditioning, what you may not know can cost you dearly.

The basic air conditioner system

Basic air conditioner system

A modern vehicle’s air conditioners may look similar to older systems, but they are vastly different. Gone forever is the clutch driven steel compressors with five-pound Freon charges. Instead we have aluminum direct drive, variable displacement compressors, often with 12 ounces of refrigerant.

Variable displacement means the compressor no longer needs to cycle on and off. Instead, if there is a clutch at all, it serves only to turn the unit off. This type compressor rotates constantly. To control cooling it varies its displacement according to demand. This allows very efficient cooling when needed and almost no drag when we do not need cooling. These units are so efficient that 12 ounces of refrigerant cools like the five pounds in older systems.

Gauge pressure is NOT a reliable indication of charge level

Gauge pressure is NOT a reliable indication of charge level

Variable displacement also means that low side pressure is no indication of charge level. The system could be over or under charged and still show proper low side pressure. The compressor simply reduces displacement to maintain desired pressure. It also means a severely overcharged system may not show that low side pressure is too high. The compressor simply works much harder in an attempt to draw the pressure down. We can very quickly damage an otherwise perfectly healthy system by adding refrigerant. Once the compressor fails, debris quickly contaminates the entire system and can cost thousands to repair.

Overcharging an AC system can cost thousands in repair

Overcharging an AC system can cost thousands in repair

An air conditioner overcharge quickly destroys the aluminum compressor. In a 12-ounce system, just three ounces of refrigerant represents 25% overcharge, which can kill the compressor. Adding an additional 12-ounces of refrigerant may cause a 100% overcharge!

To properly charge a modern vehicle air conditioner we must fully evacuate the system and then add the proper volume.

We properly recharge the system using a refrigerant recycle machine, charging cylinder and proper service data.

Air conditioners stop cooling for several reasons other than low charge. Many of these will cause additional damage if not diagnosed and corrected.

Some more common reasons include:

  Inoperative condenser fans; which will destroy the compressor.

  Restrictions in the system that deprive the compressor of lubricant.

  Poor electrical connections.

  Broken actuators and blend doors. These can cause liquid to return to the compressor.

  Bad or out of range sensors.

Proper diagnosis can uncover the problem so that we can resolve it. Adding additional refrigerant can speed up destruction of the system and the original problem remains. An air conditioner that does not cool does NOT necessarily mean the system is low on charge. Don't create needless expense; Testing is better than guessing. AGCO, it's the place to go.

Far more information on air conditioner repair and diagnosis is available in our comprehensive four-part series on the topic.





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