So I completely rebuilt my A/C system short of what's under the dash. And it does blow cold and works great. However, I'm have a leaking problem as determined by an electronic sniffer I bought. It seems to be at the aft end of the A6 compressor. And... It seems to be at that little cylinder thingy at the top of the pic. It doesn't attach to anything electrical. It's just there. Anybody have any ideas?

it's the part on top with a brown paint chip off it.

 

I don't know what that is specifically, but I have an A6 currently in the garage and I just looked at it. That hole in the end has some kind of coil in it (within the cylinder) and it unbolts with a 15 mm wrench. I think it is the oil fill hole with some kind of pressure relief. In any case, what you really want to know is whether it can leak. When you unbolt that, there is definitely, 100%, an O-Ring there which I saw with my own eyes 10 minutes ago. If that is crusty, presumably a potential leak?

 

I think your looking at the pressure relief valve which can be better seen in this pic, the brass thingy at the left 9 o'clock position




Cheers
DD

 

Yes, I unscrewed it and replaced the o-ring before putting it back together. And the sniffer goes off when I put it right on the end so it's leaking out the end.

 

I have a used A6 compressor and it has that pressure relief valve. I swapped it over yesterday, but didn't have any more R134A. So I bought two cans today and will vacuum and pressurize it tonight and see if that was the culprit.