Since the mid-1990s, most cars equipped with air conditioning have also been outfitted with electronic modules that tell your car’s AC compressor to cycle on and off. Although it may be alarming the first time it happens at a stoplight or when you are idling at the store, 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 at that moment to move the refrigerant around.
Built-in ECU Programming
You will also notice air conditioner compressor cycling when your car is under hard acceleration, like 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 is failing. Yes, it is easy to blame a mechanical system 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 temperature 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. Some of these devices are really resistor packs that will change value over time depending on 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 the ECU signals that are supposed to happen at certain points may change, leading to an alteration in your car’s compressor cycles. 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 need replacement. If you are a bit strapped for cash, you can find an aftermarket replacement module, purchase a service manual, and try to replace it yourself instead. This is only advised if you have at least some experience working with car computer systems or you could cause even more damage.
Use Service Area
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 after they’ve identified the problem. 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 free of charge.