I have a 2001 A6 Quattro 2.7T. My a/c would blow warm air after the car idled for a few minutes or was moving in stop-and-go traffic. When this happened, the temperature gauge would start going up after a while. If it got as high as 5/6, I turned off the A/C to avoid overheating the engine, and the temperature would return to normal. The problem seemed worse when the weather was hottest and the engine was already warm. The dealer replaced the "high pressure switch" and topped off the freon (although they found no leak). It seemed to help a little, but the problem persists. Setting the temp on "LO" may help a little bit but even then it could take a few minutes for the a/c to really start blowing cold air, especially if the engine is warm. Two other things that may be relevant: I know there is a slow leak in the "aftercooler (?)" (cools the turbo charger) that requires me to add about 1 qt of coolant every month (though lately it's been more frequent). Also, last night I found that the engine was still hot to the touch after the car had been sitting in the garage for 5 hours - this after having driven for a little more than an hour in normal suburban traffic on a 95 degree day with the a/c going the whole time. I've resisted fixing the cooling system problem because it's cheaper to refill the coolant. Does the coolant leak have something to do with the a/c? Are there other things that might be causing this problem. Thanks.

 

You may have an airbubble in your cooling system caused by the leak. As much as i bitch about the enginneering on these cars some parts are very well engineered. This happens to be the case here. The engine will shut off the airconditioning if it sees the engine temperature getting to hot. I believe this may be the case here. I suggest takeing care of the cooling system first. Its really a requirement to properly diagnose the air conditioner.