The first time I really "used" my A/C (i.e., extended operation at relatively high speed ~ 60 mph), I noticed a sound every time the clutch would engage. It was kind of like a small low pitched screech.

Once I arrived home and peered under the hood, I noticed that the compressor belt tensioner accessory was missing its nut. This is the little screw that you're supposed to turn in order to adjust the belt tension. The tensioner accessory was partially engaged into the slider rail, ...but the retaining nut is gone. The A/C belt is tight and not loose at all.

I didn't run the A/C and try to rev the engine to duplicate the sound because I was ready for supper. Do you think that the low pitched screech sound every time the clutch engages (at high speed) is due to this tensioner nut missing? I guess what I'm asking is ..assuming that all the other bolts/nuts on the compressor are in place, would the tensioner accessory still be necessary?
Thanks,
Cabbie2169
p.s. This is a '93 245..I have the R134 system

YOu also need to make sure your harmonic balancer (i.e. the crank pulley) has not separated. There's an inner and outer steel piece, with a rubber layer in between. The rubber cracks and the inner can slip vs. the outer.

The extra load of the AC could be enough to start the pulley slipping. If you view the pulley with a timing light, you would be able to see any slippage- you could also mark the pulley with White-out or something, and make it happen, see if the marks move.
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Rob Bareiss, New London CT ::: Roterande Fläkt Och Drivremmar!

My experience with the screech is with a B23, York compressor, but it might carry to your situation.

Engaging the clutch made a screech, and I noticed that it sort of chirped every now and then while runing. Looked at it while running, it was flapping loose - though it looked OK when still.

Tightening the belt fixed the noise.

Your other responses are all good, go for the belt check and replacement. The missing parts are likely junkyard-obtainable parts.

Good Luck,

Bob

:>)

I would check the belt tension first. If that proves OK, then I'd still suspect belt slipping due to glazing. Take a spray bottle of water and squirt it on the inside of the belt when the clutch is engaged. If that makes the sound go away, then it's a glazed belt and you should replace it. If none of this proves fruitful, then check the clutch air gap, which should be 0.3 - 0.5 mm. I think you have a Seiko Seiki compressor (unlike earlier 240s, which had the Diesel Kiki.

The purpose of the tensioner is to make it a bit easier in adjusting the tension of the belt. In fact, once the belt is adjusted to the appropriate tension and the mounting bolts are then tightened to secure the compressor (or alternator, power steering pump, etc.) the tensioner bolt can then be loosened to remove potential undue stress on the tensioner bolt.

In other words the tensioner bolt is not necessary.

I would suggest checking the tension on the compressor belt and insuring that it's at the right tension. General rule of thumb is about 5mm. Some manuals indicate 1 to 3mm. Also, check belt condition.
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dnvolvo '89 765T 200K - '91 245 100K