Why has my car's air-conditioning stopped working?

Your motoring problems solved

Mercedes-Benz S-class air conditioning fault

Q. The air-conditioning system in my Mercedes S 600 stopped delivering cool air to the cabin, and now I cannot turn it back on. A garage technician told me the level of Freon refrigerant was low, resulting in the system turning itself off and disabling the control to preclude damage. Is he right?
JW, via email

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A. Probably. Apart from being the cooling agent, or refrigerant, air-conditioning fluid lubricates many of the moving parts in the climate control system, so it is quite common for cars to prevent you from turning on the AC when the fluid is low, to avoid further (expensive) damage.

There are two probable reasons for the low fluid level. If the system is not used for long periods, the rubber seals can dry out, leading to fluid slowly leaking out and evaporating. Often this is only temporary, as seals regain their integrity once the system is on and fluid is circulating. This is why it is important to turn the AC on for 10 to 15 minutes every week, even during the winter.

But it’s also possible that a faulty component has recently developed a leak, or a seal has failed completely, which will need to be identified and repaired before the system is refilled.

You don’t necessarily need to go to a Mercedes dealer to find out what your car is suffering from; most garages can do the job.

The standard procedure is to empty your car’s air-conditioning system and see how much fluid is present. If it is very low, make sure the garage checks for leaks and that the seals haven’t dried out.

If the fluid is more or less at the right level, however, the fault will lie elsewhere and further investigation is needed.

Sunday Times Driving Car Clinic: Tim Shalcross, advance driving advice

Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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