Why is my AC not blowing cold?

The air conditioning system in a vehicle is subjected to much more abuse than your typical household AC system.  Between the constant hot and cold cycles of the engine, the harsh vibrations over pot hole infested roads, and the constant dirt and debris there are a number of things that can go wrong.  These are just a few of the most common causes for AC failure.


Number 1 on the list is loss of freon.  Rubber hoses, seals, and valves are all common areas where freon will escape.  Occasionally the condenser on the front of the vehicle will pick up a rock. The seams on the evaporator inside the dash will bust from constant expansion and contraction.  There can be dozens of different o-rings and seals that may fail.


The biggest problem we see with freon leaks typically happen when freon is added to the system without a charge of oil.  When freon leaks out of the system, so will the oil that lubricates the AC compressor.  Once the oil in the compressor drops below a safe level catastrophic damage will occur causing metal particles to migrate throughout the system.  These metal particles need to be flushed from the system or they will quickly ruin any subsequent compressor installed on the vehicle. 


Number 2 of the most common problems is an electrical system failure.  There is a system of switches and relays in the vehicle that provide feedback to the vehicle which control compressor operation.  The system is designed to run at a certain pressure and when the pressure is outside of the normal ranges the vehicle will shut down operation of the compressor to prevent damage to the compressor.  If one of the switches provides improper feedback then the system will not operate properly.


The first thing a reputable shop will do is determine whether or not the system has a proper charge of freon.  If the freon level is low then a dye will be added with the oil in the system to determine the location of the leak.  If the freon level is correct then the control system will be inspected with sometimes complex electrical testing procedures.  Most failures will need a compressor, expansion tube, drier, and an extensive flush to get the system running properly again.

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