AC seems to be running fine and blow's cold air as long as you are moving. when parked or stopped at a light it starts blowing hot air. Local auto parts guy said the system wouldn't take any additional freon (I thought it was low) and the compressor was bad. If that's the case it should spuraticly blow cold air right? Any advise on what to look for? thanks.

2008 A4 2.0T

 

There is something that tells the compressor to kick on and off (some kind of relay/switch). That might be going bad. Compressor could be starting to fail as well.

 

yup, theres a low pressure safety switch and a high pressure safety switch. I think the computer tells it to turn on or off if I remember correctly. But those low and high pressure switches will stop your ac.

 

Thanks for the input guy's. I may take a look at replacing the switch's first before footing the bill for a new compressor. I just bought this car a week ago (from an Infinity dealer) but complaining to them along with the other thing's I've found wrong, is liking talking to the hand. I'll never go there again that's for sure.

 

Problem last Saturday in my '06 A6. Went to dealer; they fiddled and it started blowing cold. Today, hot air again after about 18 miles. Back to dealer about 12 miles on TPKE and it started cold just before I arrived. Dealer thinks, but can't confirm it's a valve problem. It's an $800 guess! Think I will try a few more days. Of course, high heat and humidity came into Phila region today.

 

If it only blows hot when in slow traffic or stopped make sure your aux fan is coming on. If your not getting air thru the condenser it will blow hot.

 

no good check for it that I have found but many threads have pointed at the high pressure switches going bad. $30 part but need to crack open the system and re-charge when you do it. I have the part but haven't had the time to put it in yet. Will keep you posted if that ends up being the problem.