Air Con Compressor Faults: How Do You Know It Is Failing?
A failing compressor can announce itself with a rattle or squeal, a clutch that will not engage or cooling that has gone completely, but those symptoms can also come from cheaper faults.
The compressor is the pump at the heart of the air con system. Driven by the engine, usually by a belt, it squeezes the refrigerant so heat can be moved out of the cabin. When it fails you may hear it, lose the cooling or both.
Before assuming it needs replacing, it is worth knowing that several simpler problems mimic a dead compressor: a blown fuse, a failed relay, low refrigerant that trips the pressure switch, or a damaged wiring connector. Our job at Automaster, a garage at Longcombe Cross near Totnes, is to work out which one you have before recommending parts.
What are the signs of a failing air con compressor?
The compressor tends to give warning before it quits, although not every failure follows the same pattern. Pay attention to new noises that appear only when the air con is switched on, and to cooling that comes and goes.
If the noise changes or disappears when you press the air con button off, the compressor or its clutch is a prime suspect.
- Grinding, rattling or squealing that starts when the air con is turned on
- Compressor clutch that does not click in, or engages then drops out
- Warm air even though the system has gas
- Visible oil around the compressor body
- Belt noise or a belt that wears quickly
Why do air con compressors fail?
Wear is one cause, but the commonest underlying reason is lack of lubrication. The compressor relies on oil carried around with the refrigerant, so a system that has lost gas through a leak may starve it. Running it low for long periods can damage the internal parts.
Moisture or debris in the circuit, a seized clutch bearing and age all play a part. When a compressor breaks up inside, metal particles can spread through the pipes, which is why the repair is often larger than a simple swap.
Can the compressor clutch be replaced without the whole compressor?
Sometimes. If only the clutch or its coil has failed and the compressor itself turns freely and has no internal damage, a repair to the clutch part may be possible. Whether that is available depends on the make and model of your car, so we would need to inspect it first.
If the compressor has failed internally, replacement is the normal route, and we cannot promise which option applies until we have seen the system.
What does compressor replacement involve?
The old refrigerant is recovered, the compressor is removed and a new or reconditioned one is fitted. Where metal debris is suspected, the pipes and other parts may need flushing or replacing, and components such as the receiver drier or expansion valve are usually changed so the new compressor is protected.
After that the system is vacuum tested, refilled with the correct refrigerant and oil for the vehicle, and checked for leaks and cooling performance. The cost is driven by the price of the compressor for your model, how much of the system needs cleaning or replacing and the labour needed to reach it, so please ask us for a quote.
Is it safe to drive with a faulty air con compressor?
Often yes, but it depends on the fault. If the compressor has seized, its pulley can drag on the drive belt, and that belt may also run the alternator or water pump on some cars. A squealing or smoking belt means you should stop and have the car checked.
If the only symptom is no cooling, you can generally keep driving while waiting for an appointment, and leaving the air con switched off will avoid putting load on a damaged unit. A warning light, overheating or loss of power steering is a reason to stop at once.
A compressor fault is not always a compressor replacement, so testing first saves unnecessary parts. Ask Automaster for a quote or call the quote line and tell us what you can hear and feel.
Common questions
Why does my air con compressor not turn on?
Possible causes include low refrigerant, a blown fuse, a faulty relay, a damaged pressure switch or a failed clutch. A garage tests each in turn, starting with the simplest to rule out.
Is a noisy compressor always about to fail?
Not always. Some noise comes from the belt, a tensioner or a pulley bearing. However, a new grinding noise that appears with the air con is worth having checked before it gets worse.
Can low refrigerant damage the compressor?
Yes. The oil that lubricates the compressor travels with the refrigerant, so running with too little gas can wear it. This is one reason to have a poor performing system looked at sooner rather than later.
Do I need the whole system replaced if the compressor fails?
Not usually, but it depends on whether debris has spread.
More advice
Ask for a quote
Tell us the make, model, registration and what the car is doing, and we will come back to you. Prefer to talk? Call our quote line on 01803 862152.
Automaster, Longcombe Cross, Longcombe, Totnes TQ9 6PL, United Kingdom