It's Hot Already


A few hot days under our belts and the requests for air conditioning repairs are rapidly growing. There are very few vehicles out there without air conditioning. In many vehicles these days it is not even an option. The tax collectors still consider it a luxury though. I know many of you consider it a necessity. I know some people that prioritize air conditioning over brakes and tires.

As is true with most vehicle systems the air conditioning system is more reliable than it ever was. Also, as with most other automotive systems, it is more complicated than it ever was. So when you tell your mechanic that your air conditioning is not working followed by “How much will it cost to fix it?” You may be faced with a blank stare. The possibilities are literally endless.

It is not likely you would accept a rough estimate that starts in the tens of dollars and ranges to the thousands, but that is reality.

Electronics and computer controls have invaded your air conditioning system just as they have invaded every other vehicle system. Expect your mechanic to request some time to diagnose the system.

If your vehicle was made in the last fifteen years expect that a computerized diagnostic tool will be your mechanic’s weapon of choice for a hasty diagnosis. It may even be used before turning on the vehicle and actually verifying a problem. He/She may not even lift the hood.

Almost every vehicle made in the last ten to fifteen years is a network of computers that talk to each other. Each computer will likely be in charge of a particular system. As far as air conditioning is concerned there will likely be an HVAC (Heating Ventilation and Air Conditioning) computer. That HVAC computer is definitely not the lone wolf in charge of keeping you cool though.

Sure, when you push the button to turn on your air conditioning, that input will be sent to the HVAC computer. At this time though some other computer systems will become involved. The HVAC computer prudently will check out some conditions before invoking any commands. What is the temperature outside? Too cold and I won’t turn on air conditioning no matter what. How is the engine temperature? I will ask the engine computer for that little tidbit of information. If the engine is too hot and close to overheating and I turn on the a/c the load on the engine will increase (air conditioning requires power) and worsen the overheating condition. So, no a/c when the engine’s too hot.

Throttle pedal on the floor? You want maximum power. No a/c.

What about refrigerant pressures? If you are at all familiar with checking air conditioning systems you are used to seeing a technician hooking up a pair of pressure gauges to your a/c system. These gauges will indicate the proper fill of refrigerant and function of the a/c system. While your fancy new vehicle may have built in pressure sensors. It is likely that your mechanic will be looking at those pressures on a laptop connected inside your vehicle. If the pressures are too high or too low guess what? No a/c.

Given all acceptable inputs (temperatures, pressures and what have you) the HVAC computer gives the go ahead to the engine computer to turn on the air conditioning compressor. The engine computer obliges with a command to engage the compressor clutch.

Voilà! Cold air!

What could go wrong? Bad compressor clutch maybe …?

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