aux belt pulley squeak - only when ac is running

[jlmacd]

Hi all. I have been chasing the ubiquitous Aux belt squeak/chirping sound on my 2.0 HDi 110. I have discovered it is only present when the AC is turned on and compressor running. Turn the AC off and you can hear the load on the engine ease and the squeaking goes away. Is this going to need a new AC pulley or could the belt be the culprit?

Had originally thought, from good advice given on the forum, that the crankshaft pulley may be failing but there is no evidence of the harsh metallic sound folk describe signifying the crank pulley is disintegrating. To be honest though, I have not got the wheel off yet and gone in for a closer look for the evidence of the brown dust indicative of it wearing down.

Given the fact the sound is only really present with the AC running, should I be looking to this first?

Many thanks for any thoughts ....

[Doggy]

Might just be the aux drive belt.
Given that it's a PITA to change the compressor, (loss of gas), I would be tempted to swap the belt , (or spray it with some drive belt spray if you can get any cheap).
May not work, but it won't cost much and you'll kick yourself if you try something more expensive/involved first.

[jlmacd]

Thanks for the advice Doggy. Changed the belt today and squeak has gone! I did notice though that the tensioner pulley is 'bouncing' at tick over. This stabilises once the revs are increased slightly, prob over 1200+, but returns when back at idle. Don't imagine this is normal - any idea what the fix may be?

[PeterN]

Could be a sign of crankshaft pulley failure, as the revs increase the pulley tends to centralise. If you can get close enough to it, look for cracks in the rubber insert.

Peter