What to Do If Your Car's AC Begins to Short Cycle

In the baking heat of an Australian summer, you may be thanking your lucky stars that your car is equipped with a healthy air conditioning system. You simply wouldn't be able to survive during your afternoon commute in stop/start traffic without it, even though you take it for granted. However, one day you may notice some very strange behaviour, as the system seems to be cycling on and off for no reason. What's going on, and how can you fix this quickly before the mercury goes off the scale?

When Short Cycling Is Normal

In some situations, this type of behaviour is quite normal and is to be expected. Air conditioning systems in some cars have sensitive electronic modules that cause the compressor to function like this, especially when the interior temperature of the cabin is near to its optimal figure. In short, the system is simply taking a break until it is needed again.

You may also notice this behaviour when you are accelerating hard to overtake slower traffic. At this time, the vehicle's 'brain' pulls all of its resources from any backup systems to give the engine the power it needs to complete the manoeuvre. As a result, you may notice that the compressor cycles on and off.

Resistor Failure

However, if the compressor seems to be erratic for no apparent reason, then you may have an emerging mechanical problem.

Some of the internal components are not meant to last forever, and they will also suffer from high external temperatures. When this happens, the resistors fitted inside the control module will change their characteristics and will begin to send conflicting signals. Eventually, the ECU will interrupt the compressor cycle and cause this strange 'on and off' motion.

Don't Just Sit There

If you let this continue without intervention, the resistors will wear out completely and will cause a complete shutdown of the system. Therefore, as soon as you notice these early warning signs, you need to move quickly if you are to retain the right internal temperature, as well as your sanity.

What You Need to Do Next

Generally speaking, this is not something that you can fix yourself as it requires special equipment to analyse the problem and pinpoint the faulty resistor pack. Your best course of action is to pick up the phone and schedule a visit to your mechanic for a full car air conditioning service.