I recently bought a 2004 A6 2.7T. The A/C works perfectly well as long as the car is moving, but when the car stops in traffic it starts blowing hot air relatively quickly. If I put the car in neutral and rev the engine that doesn't seem to have any effect. Thinking that it may be low on refrigerant, I bought a canister of refrigerant that came with a gauge and plugged it into the low pressure intake as instructed. But the gauge shot up into the lower portion of the red zone indicating that there was perhaps too much pressure in the system. While troubleshooting I also noticed that when the Economy switch was turned on (i.e. the compressor is turned off) and the car was stationarythe system blew hot air, even with both thermostats set to LO and the outside air was in the 60s. Any ideas what could be my problem?

Not sure if this is relavent, but I have also noticed that the engine seems quite hot after a 1 hour drive home from work. Both the water and oil temperature gauges on the dash read in the middle of the temperature zone, so it doesn't seem to be overheating. My previous car was a 1998 2.8 A4 and I never noticed that kind of heat coming off of that engine, so I was wondering if the 2.7T engine just runs hotter?

Thanks in advance for any advice or thoughts.