I've got a 2000 A6 Avant quattro with the 2.8l ATQ engine. I've been trying to repair after some front end damage. Latest thing I've noticed now that it is getting warmer here in upstate NY is that the AC compressor is not kicking on. Tried cycling the Econ button, but nothing. I'd like to at least troubleshoot a little on my own before bringing into the shop. From what I've researched, could be a multitude of problems from fuse, relay, hi/low pressure switches, compressor clutch, or the compressor itself. A lot of the info I've read notes the need for AC manifold gauges to measure the hi and low pressures. Since the compressor won't turn on, is it still a good first step to measure the hi/low pressures or are there more logical electrical tests to conduct. Thanks in advance for the help.

 

The first thing to check is the refrigerant pressure. If it is low, the compressor will not start.

 

Thanks for the reply. I did run a quick test to make sure the AC compressor and clutch were functional. Based on some other advice, I unhooked the single wire connector in the cluster near the power steering reservoir. Did a quick jump front the connector to the Positive terminal on the battery. Got the click I was hoping for. Also tried it with the engine running, heard click and saw the clutch engage, turning the compressor. So, good news that the compressor and clutch are OK. Guess the problem is most likely low refrigerant. I am debating trying the quick refill strategy now. Must have been or is still a leak in the system. My thought was to get an AC manifold gauge set from harbor freight as well as a air vacuum pump. My understanding is that it is really important to purge the system of air and moisture and the vacuum test should show it able to hold a vacuum of 27-30 Hg before adding more refrigerant. Does this sound reasonable or should I just try the quick refill to see if it may get the system working. I don't have long-term plans with the car, really just hoping to get another year out of it and would like the AC working at least through the summer. So, obviously looking for the cheapest alternative at this point.

 

The cheapest alternative is to have a shop refill it and check for leaks (about $60). Unless you are trained with equipment, you can do a lot more very expensive damage than you think. Messing with AC systems is not for the occasional mechanic.