My 2001 A4 Avant is within 2 weeks of the end of its certified warranty, and I am having mysterious problems with the thermostat and AC. The thermostat is incorrectly reading the exterior temperature on a hot day sometimes as low as -40, and so shutting off the compressor and blowing hot air into the cabin.

I had the dealer replace the exterior sensor about a month ago when I was getting incorrect readings, but now I am getting crazy intermittent episodes where all of a sudden the sensor temperature steadily dives to -40 degrees. Sometimes it eventually creeps back up and ultimately the compressor comes back on, but yesterday I spent three long hours on the highway with no ac and 90 degree temperatures with the car happily reporting readings more appropriate to January than August.

This morning I drove bright and early to the dealer, and of course it worked fine from a cold start and he can't find anything wrong. Does anyone have any ideas as to what might be causing this?

Yesterday the car had been sitting in the hot sun all day before I got in, so I wonder if the heat had somehow overloaded the controller or sensors?

 

just had a car like this today. was an 05 or 06 a6. ambient temp reading -33 on a 95F day. The a/c wouldnt work as well. LOL.

I dont know what they did to it but when i test drove it it worked great.

Anyway, the dealer really cant help you unless you can duplicate the problem and drive right to them. Then im sure they will take care of it.
Its just very hard to diagnose something that isnt there ya know?

 

Dealer was able to replicate the problem after one of his techs drove the car home and spent over an hour on the road. He suspects it might be the inside temp sensor and has ordered a new one. I am dubious because the outside temperature is reading way off on the dash display...