Mechanically Speaking: What happened to my AC?

There are a myriad of reasons for the lack of AC (air conditioning) function.

A couple of hot days are under our belts. At the shop this means the phone is ringing and a common concern is the lack of air conditioning.

“It was working last year but now I’m cooking. What happened to my air conditioning? I have not used it since September. It was fine then.”

There are a myriad of reasons for the lack of AC (air conditioning) function.

Even if you thought you did not use it since that last hot day in October you are probably wrong. If you used the defrost position of your heating system on an above zero day you likely invoked the services of your AC system. In this scenario the AC is used to dehumidify the air entering the vehicle.

The process of cooling air removes moisture (scientific fact). Dry air defogs windows a heck of a lot quicker than moist air.

So, in all likelihood your AC did not have the winter off. In some ways that is a good thing. One big expensive part of the AC system is called the compressor. This is a rotating pump that is probably happier rotating than sitting still. Pumps that sit still get leaking seals and a leaking pump seal is one of the common reasons your AC is not working.

It is likely that your fully functional AC system failed or stopped sometime during the winter and when it did fail it went unnoticed. Unless you are very observant it is difficult to recognize failure. Your car was warm all winter.

What happened to your air conditioning system over the winter? Odds are it ran out of refrigerant but that is not the only possibility.

The refrigerant contained within the many AC system components is under pressure. Ready, willing and able to escape. The components trying to hold in the refrigerant are less than perfect at their job.

There are rubber hoses. As many of you know, gas molecules can find their way through solids like rubber. Slowly, over time they sneak through. More likely they will sneak between the rubber and aluminum at sealing surfaces. With age seals get hard and crack.

There is also a component called the condenser. This component is almost always mounted directly in front of your vehicle’s radiator. If you look straight into your vehicle’s grill you will see this finned aluminum heat exchanger.

Every bit of sand, rock, and salt spray kicked up from behind the vehicle you are following is pelting that condenser. The materials that make up the condenser are thin to aid in heat transfer. Thin and fragile. One good size piece of Kootenay road sand can put a pinhole in that condenser. There goes your refrigerant, there goes your air conditioning.

Refrigerant loss is not the only reason your AC may not be functioning. As in all automotive systems electricity is involved. There are switches, sensors, modules, wires.

A little corrosion on a connection and your AC system is rendered useless.

As you can imagine there is a very large price difference between replacing a condenser or a compressor verses cleaning or replacing a connector on a switch.

The difference between having a cool windows-up summer and sweating through that two week hot spell may be a tough decision.

Trail’s Ron Nutini is a licensed automotive technician and graduate of mechanical engineering from UBC. E-mail:

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