Sunday, April 20, 2014 Detailed Auto Topics
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Every year well intentioned folks try to recharge their vehicle air conditioners. 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.

Basic air conditioner system Modern vehicle air conditioners may look similar to older systems, but they are vastly different. Gone forever are the clutch driven steel compressors with five-pound Freon charges. Instead there are aluminum direct drive, variable displacement compressors, often with slightly more than 12 ounces of refrigerant. (please click on images for closer view)

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. The compressor rotates constantly and varies its displacement according to demand. This allows very efficient cooling when needed and almost no drag when cooling is not needed. So efficient that 12 ounces of refrigerant cools as well as five pounds in older systems.

Gauge pressure is NOT a reliable indication of charge levelVariable 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 throttles back to maintain desired pressure. It also means a severely overcharged system may not indicate that low side pressure is too high. The compressor simply works much harder in an attempt to draw the pressure down.  An otherwise perfectly healthy system can be very quickly damaged 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 repairThe problem is, 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 one additional 12 ounce can of refrigerant may cause a 100% overcharge!

The only way to properly charge a modern vehicle air conditioner is to fully evacuate the system and then add the proper volume. 

Proper recharging is done using a refrigerant recycle machine, charging cylinder and proper service data.

Air conditioners stop cooling for a number of reasons other than low charge.  Many of these will cause additional damage if not diagnosed and corrected.  Some of the more common include:

 Inoperative condenser fans; which will destroy the compressor

 Restrictions in the system; deprive the compressor of lubricant

 Electrical connections

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

 Bad or out of range sensors

Proper diagnosis can uncover the problem so that it can be resolved. Adding additional refrigerant can speed up destruction of the system and the original problem remains unresolved.  An air conditioner that does not cool does NOT necessarily mean the system is low on charge.  Don't create needless expense; Test don't guess.  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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