Aux belt failure, what cuased it. Tensioner, Air con or PAS
 

Hi,

Driving back from holiday with the caravan my alternator belt snapped, battery light came on and steering became heavy(Alternator not charging and PAS pump not being driven). I'll explain what parts were damaged and I'd appreciate if someone could help explain what caused the failure in the first place.
Further investigation showed that the plastic tensioner pulley was 'melted' (can't upload photo as minimum size my phone takes is 800kb and max allowable here is 370kb) with grooves melted into it but with bearing still turning freely. The plastic PAS pump pulley had also taken a hammering but not as bad as the tensioner pulley and PAS bearing still seemed to turn ok(but hard to tell as it is still connected to the system so has resistance. The plastic idler pulley was ok with no marking and the bearing turning freely.The steel crank, alternator and Air Con pulleys all seemed ok but with some plastic and rubber debris in the grooves.
Now another point of interest is the air con pully is very rough and graunchy and I can move the pulley axially 1mm on the air con clutch assembly. Surely this is not normal? I started the car(with out aux belt) and put air con on full just to see if the pulley tightened up(clutch engaged) on the air con pump but it didn't.
Until I discovered this air con pump issue I was a bit puzzled as to what had failed first because all other pulleys seemed to be turnimg freely. Soon after suspecting the air con pump I noticed that the engine and belt rotates clockwise so if the air con pulley was to blame the belt would have to pass round the crank first then it would go round the idler(which was ok), then round the tensioner pulley(which was melted) so if the air con pulley was seizing why would the belt not melt the idler pulley first as it ewould be the first plastic pulley to see the hot belt? I then realised the side of the belt that contacts the air con pulley does not touch the idler pully face but it does touch the tensioner pully and the PAS pulley. So it may well be the Air con pump.

Anybody any ideas? Is it a common failure for a failed air con pump bearing(if it is failed) to wipe out the rest of the plastic pulleys this way? Can the tensioner fail and cause this and the tensioner bearing still be ok?

I've about to change PAS pump as the pulley was shot and I've also changed the tensioner and idler. Depending on what is advised in the forum I'll change the air con pump. These air con pumps are on ebay for under £200 from 'coolpartsuk' has anyone bought one of these pumps? Any advice oh where to buy air con pumps?

Thanks

Tony

Do you have the belt? Did it snap or just come off?
It sounds like the tensioner bearing has dried out, overheated, melted the pulley, which has distorted and thrown the belt off...
Have you checked the alternator pulley? Itll be a freewheel pulley, they go bad and don't freewheel anymore, overloading the belt and tensioner.

Thanks for comments. Belt snapped and alternator pulley/bearing ok. Tensioner bearing runs freely now-maybe it did overheat before. But about air con pump stiffness and roughness in bearing?

I dont know about the pump im afraid! But, I cant see that being involved with melting the pulley, which would appear to be the reason the belt vacated...

A seized pulley on the air con compressor was the culprit when mine went.