AC Squeal

So my AC is squealing when the compressor is engaged. I thought it was the alternator pulley going bad, based on this thread, so I went ahead and had the alternator pulley replaced when I had the 20k mile service done last week. Just got the car back yesterday, and after having the alt pulley replaced the squeal didn’t go away. The squealing has been intermittent starting maybe 2 months ago, but it seems to be getting worse. The squealing goes away immediately and completely when the AC compressor is turned off even with the AC fan still blowing air in the cabin. When the AC engages, sometimes there is a really loud shrieking squeal (loud enough that it is a parking lot head-turner) that can last for 10-20 seconds, and sometimes it is much quieter and can only hear it with windows down or when standing outside next to the car. Also, sometimes it will go away completely while the AC is engaged, but at other times it continues at the low volume the whole time until the compressor cycles off.

I should also add that starting a couple months ago that the AC compressor sometimes wouldn’t come on after starting the car. It would take 5-15 minutes before it would come on. Before I was aware of the squealing sound, and/or when I thought it was the alternator pulley and unrelated, I was thinking the 384 relay was going bad with the cold solder joint. It could still be a bad 384 relay as a side-issue, but not sure now if it might be related to the squealing problem. Like if the AC clutch isn't wanting to engage or something.


When the AC is running, it blows ice cold air.

So before I take the car back to the shop to be told the compressor must be replaced, I thought I’d first check in with the B5.5 experts here. Does this sound like something obvious that can be repaired without having to replace the whole compressor? Such as compressor clutch? Something else? Anything easy I can do to trouble-shoot and diagnose? Any suggestions would be welcomed.


Thanks. I appreciate all the contributions from the experts here.

The tech who works on my car checked the belts and said they all looked good and none were loose. He's not really an AC guy though so didn't do any trouble-shooting beyond changing the alt. pulley that I asked him to do and also checking the belts. I was going to take the car to another VW specialist (non-TDI), but wanted to check here first to see if it might be something that is somewhat common or easy to diagnose.

Ac has different belt from alternator

My belt is tight and the a/c occasionally squeals. I have to turn it off for a sec and back on. Going to replace the belt soon and see if that fixes it.

I know this is my thread and then i went silent, but the AC compressor pretty much stopped coming on altogether after my original post so the squealing of course stopped also. That supports the possibility of the 384 relay being bad, but I just haven't had a chance to pull it and re-solder it. I say "pretty much" b/c the AC did come back on this morning, but we are in a bit of a cold snap at the moment and as soon as the heat comes back I expect the expansion/contraction issue with the 384 solder to disconnect the signal again.

There's a certain logic to QuickTD's hypothesis about the cold solder first starting to crack where it may have been intermittently and rapidly turning the compressor clutch on and off. Once cracked it just stopped sending the signal altogether.

Anyway, I will re-solder the 384 relay this evening or weekend and then triple-check the tension on the AC belt. Thanks guys.

I have a question in regards to AC function in the b5.5 tdi. Are there circumstances where the AC will cut out by design? Example...under WOT. Or perhaps if the car is over heating...? Mine seems to cut out if I stab the throttle pretty good from a stop and rev over 3500 rpm. But I'm necessarily applying WOT though. Normal or cracked relay?

Most vehicles will cut the ac at the point where passing gear comes in.

The Engine controller has the ability to send an A/C cut out request to the retardation relay, under high load, high RPM, or if the coolant temp is too high.

Had an AC squeal on mine and now no AC after just servicing it! But im almost certain the clutch is shot on the compressor as is smells like a burnt clutch and has some debris, does seem to engage somewhat tho, I dunno. any known rebuild parts to do it, or any advice as ive done lots and lots of car work, i don't recall ever changing out an AC clutch tho!