What to Do When Car AC Compressor Cycles On and Off

Since the mid-1990s, most cars equipped with air conditioning have also been equipped with electronic modules that tell your car’s ac compressor to cycle on and off. This is a very normal operation.

Although it does seem alarming when it first happens to you at a stoplight or when you are idling at the local Wal-Mart, it is very normal. The electronic module in your car’s air conditioning system is informing your car’s compressor that it can take a break because the car has reached the interior temperature you have chosen and the compressor is not needed to move the refrigerant around.

Built-into ECU Programming

You will also find air conditioner compressor cycling happening when your car is under had acceleration as when you are pulling onto a major freeway. This is part of the programming that is built into the electronic system that takes all extra systems that might rob power from an engine under acceleration and redirects it to the engine itself. Again, this is normal operation.

If you do find that your car’s air conditioner compressor is cycling on and off too quickly, then it likely indicates that your vehicle’s electronic module may be failing. Yes, it is easy to blame a mechanical system for failing but your car’s compressor system is engaged by the clutch and that, in turn, is driven by the ECU (electronic control unit) for the air conditioner/heating system.

Reasons for Failure

Why would this system fail? It could be heat related. As systems age, they become more susceptible to failure, especially heat or cold related failure. Although it isn’t really advisable to look inside the module, if you could tear the cover off you would see a bunch of tiny dark chips on the board with numbers on them. Certain of those devices are really resistor packs and they will change value over time, especially in the car’s operational environment (engines are not conducive to longevity for many devices because of the heat/cold cycle they run through).

Once a resistor pack (or thermistor – it’s temperature-controlled cousin) changes value, then signals that are supposed to happen at certain points, may happen much sooner and thus your car’s compressor cycles on and off.

The solution to this problem is to take your car to a service area where they have the computerized equipment that will tell them the modules that have failed and that have to be replaced. If you are experiencing rapid cycling then, the only thing you can do is either find an aftermarket replacement module, purchase a service manual and try to replace it yourself.

Use Service Area

Or, since it is better to let the professional handle this – it is their responsibility to make it work – let your service area take care of replacing the module. They will have the right part on hand and can get you on your way quickly. Best of all, you will not have to think about it as the work is finished and the cycling should have stopped. If not, bring it back and they will have to fix it at their cost.