air con humming

audi0001

Member
hope some one can let me know if my problem is normal or not,when using my aircon it is practicaly silent but after a while a humming noise starts and then stops after 30 seconds,when i turn the engine off you can hear the humming noise then it slowly dies down,any help would be great,cheers folks
 
Hello Audi0001,

This is quite normal at this time of the year when the temperature is well into single digits. What you are hearing is a heater, which kicks in during cold weather to help bring the engine up to temperature and keep it there.

When the weather warms up, the noise will stop.

John.
 
Hi audi0001,
John beat me to it and I would certainly agree with his comments, providing you have one of the earlier diesel models that is. If its a petrol car then i'm not sure what it could be.
The heater is like a miniature central heating boiler which burns diesel. This works automatically when temps are below 5 or 6 degC and does make the sound you describe

Cheers Spike
 
The early tdi's are probably less economical in winter driving because of the diesel fired water heater, but not by much. I'm sure they warm up quicker which is good for comfort, engine life and economy but burn extra diesel in doing so.
Later cars have an extra electric heater - which I think only warms the interior and not the engine. The alternator will work harder to provide the power, which in turn will cause the engine to use more fuel.
Overall, I think the fuel consumption on my car increases by approx 5mpg in winter, partly due to the heater and the rest due to increased drag of cold tyres, bearings, transmission oil etc.

Cheers Spike
 
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