Why Car Air Conditioning Fails in the Build-Up
Air conditioning fails when it is asked to work hardest, which is why it always seems to go in October. The pattern of failure tells you the cause.
Car air conditioning almost never fails in July. It fails in October and November, and there is a reason that is not coincidence.
A system that has quietly lost some of its capacity, or has a partly blocked condenser, will still keep you comfortable in mild conditions. It has margin. As the build-up arrives, the demand goes up and the margin disappears, and the same fault that was invisible in winter becomes the thing you cannot ignore.
So the failure usually is not new. What is new is the demand.
The pattern tells you the cause
Before anybody quotes you anything, notice how it fails. There are three recognisable patterns and they point in different directions.
Cold when moving, warm in traffic. This is a heat rejection problem. The condenser, the radiator-looking part at the very front of the car, cannot shed enough heat. At road speed there is enough airflow through it to cope anyway; in a queue there is not. Usually the condenser is blocked with road grime, insects and salt, or corroded, or a cooling fan is not running when it should be. That last one is an electrical fault, not an air conditioning fault.
Weak airflow from the vents, air is cold if you hold your hand right at the vent. That is a cabin filter, and in this climate they choke fast. It is the cheapest fix in the whole subject and an astonishing number of cars are running one that is completely blocked.
Cools, but less than it used to, everywhere, all the time. This is the one that is genuinely likely to be refrigerant charge, and it is where the next section matters.
A regas is not a repair
An air conditioning system is sealed. It does not consume refrigerant the way an engine consumes oil.
If the gas is low, it escaped. Putting more in without finding out where it went means paying to fill a system that will empty again, and the second time you will have paid twice.
Sometimes a regas genuinely is all it needs. Systems do lose a small amount over many years through seals and hose permeation, so a twelve year old car that has never been touched may simply be due. But a car that was regassed eighteen months ago and is warm again has a leak, and the leak is the repair.
The right order is to test first: put the system under vacuum, see whether it holds, and where it does not, find the leak with dye or a detector. Then you can decide with real information.
Two things about gas
Newer vehicles use a different refrigerant from older ones and they are not interchangeable, so the workshop needs equipment for your type.
And there is no such thing as topping it up a bit. The correct charge is a weight the manufacturer specifies, and it is not approximate. Overfilled systems cool badly for different reasons than underfilled ones, and the pressures go somewhere the compressor will not enjoy. Proper practice is to recover, evacuate and put back exactly what it calls for.
The car air conditioning page covers what that involves and what tends to be wrong on cars around here.
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Ask us about your car specifically
General advice only goes so far. Tell us the make, the kilometres and what it is doing, and you get an answer about your car rather than about cars, including whether the job is worth doing at all.
- Workshop hours
- Monday to Friday, 7:30am to 5pm
- We cover
- Cairns, the southern corridor to Gordonvale, and north to Trinity Beach
- Vehicles
- All makes, petrol and diesel, including 4WDs and work utes
- Send the make, model, year and roughly what the odometer reads. Half of what decides a price is which service interval the car is up to, and none of that is guessable from the model alone.
- Say what the car is doing and when it does it. A noise that only turns up cold is a different fault from one that only turns up hot, and that single detail regularly saves an hour on the hoist.
- The number you approve is the number you pay. If the job turns out bigger once it is apart, the work stops and you get a call, rather than a larger invoice at the end.