Hello hello, I hope someone can help me with an A/C problem I have with my audi... I've got an 1999 A6 2.8 Quatro that was recently in an accident, after which I had to replace the radiator and the condenser. While waiting for the new parts to arrive the A/C system was open and exposed for about 2 weeks. After installing the condenser I refilled the A/C system with 4 ounces of oil because I though there was some already in there, and AIR 134A, but the i never used a vacuum pump to remove the moisture. Once i recharged it, and turned the A/C on AUTO, the compressor clutch turns on and then wouldn't stop working, no matter how much time has passed. When i put it on ECON, it turns off. Now I am not sure why it wouldn't stop working when its on AUTO. I was thinking it might be the A/C low high pressure switch, but Im not sure. Anyone have any idea why this might be happening? Thanks in advance!

 

Did you hook up a r134 manifold gauge set to monitor the high and low pressure lines? The compressor turns on when set to auto and turns off when set to econ as expected. You feel it's running too much? If it over-pressurizes and the high pressure switch has failed (which would prevent the compressor from running) but lets assume it failed and allowed the compressor to run, if the system over-pressurized, it would vent r134 from a relief valve on the compressor. When that happens, you will know. You ever been around a high pressure cooker when it vents out it's relief valve? Trust me, you'll know.

If the r134 level is low, the compressor will cycle rapidly. If the low pressure switch fails, it will prevent the compressor from engaging.

Not evacuating the air out of the system and allowing it to be exposed to the air for 2 weeks will only provide more work for your receiver/drier. It would be best to replace the receiver/drier and evacuate the air before refilling. Any local AC shop will evacuate and refill for a small charge.

the A/C will always be allowed to cycle on whenever the econ button is not illuminated, it will also be allowed to run regardless of the econ button status when set to the defroster setting.

 

Hey thats for responding and giving advice man! Today I got a pressure gauge and I attached it to the low and high ports. With outdoor temp 40 degrees Fahrenheit, and the car running (and A/C on AUTO) the low pressure comes up as 35psi and the high pressure comes up as 100psi. No matter how much time passes they remain at the same psi, both of them. When I turn the A/C AUTO off, the low pressure rises to 40psi, and the high pressure falls down to 75psi. I also replaced the low/high pressure switch with a new one I bough, and there is no difference. When I put it in AUTO, the A/C fan goes on right away and the compressor goes on as well, and the fan wont turn off before the compressor turns off.... So they are working non-stop pretty much. I disconnected the A/C pressure switch, to see if it will stop working. The compressor turns off, but the fan continues working. Sorry to spill so much info on you, but I think that perhaps the compressor might not be working properly because it doesn't raise the pressure, and it stays at 100psi. And where you said I should check the relief valve, and nothing is coming out. So overall its very confusing what the problem might be, if its the compressor or an electrical one, and Im thinking of just getting a new compressor to see if that will fix the problem... Any suggestions? Thanks in advance.