Engine very loud when AC is running.

[twoeggsovereasy]

Hello all,

Have a 1990 325is, entirely stock, and up until this week I haven't used the AC. Confirmed it had been R134a converted, and the compressor clutch engages/disengages correctly, and charged it up with some AC Pro. Everything works correctly now, and the air blows cold, but when I engage the AC while driving the engine noise seems to increase quite a bit. I've confirmed the aux fan is turning on and off as it should while the car is parked and idling, but when I'm driving the engine noise starts up as soon as I turn the AC on. Turning AC off doesn't decrease the noise, but turning the car off and then back on returns engine noise to normal. I've read that the Aux fans are very loud, is that all I'm looking at? I can't find anything obviously wrong, but the car sounds like a damn truck when I'm driving it with the AC on. Thanks!

[tomstin]

Try unplugging the aux fan. If it's original, the bearings are probably shot. Strange it would stay on after turning the AC off.

[varg]

What kind of noise is it? The aux fan is plenty loud when in good shape let alone with bad bearings, which is probable as tomstin said, but it's a constant noise so it's fairly distinct from engine noise. I'd pull the fuse for it, instead of unplugging it, that would be a fast way to eliminate it as a noise source. There are plenty of reasons for a general noise increase to happen with the AC on, if the idle drops because the ICV isn't working as it should the transmission rattle will get louder, if the compressor bearings are shot that will make noise, if the coolant temp rises the fan clutch will tighten up and the fan will make more noise, that's why the question is what kind of noise is it.

[twoeggsovereasy]

Thanks guys. Noise is like a deeper exhaust tone, like the engine is pulling more than it should. Don't notice it at idle, but it's very apparent when I'm driving. No change in RPMs, and i keep my ICV pretty clean, haven't noticed any issues there. Will pull the aux fan fuse and see how that does. Could be the fan clutch, engine runs a touch hotter with the AC on, but nothing outside what you would normally expect. If it was compressor bearings I'd think the noise would go away when I turn AC off, as the clutch looks like it's working correctly, at least when I'm parked. Will run it and check that clutch is disengaging after driving too.

[twoeggsovereasy]

Update: Disconnected aux fan fuse and that seemed to quiet it down a little bit. Also did the newspaper test on fan clutch at temp and it looks like that is bad. Assuming noise was a combination of the aux fan and a bad fan clutch.