AC Compressor operation info

[Gnasher]

Hi Guys
This may be a silly question, and I have tried searching for the answer, but with the AC turned off in my 97 Disco V8, the compressor pulley stops going round, so the serpentine belt is dragging across it, turn it on, and the pulley goes round and AC goes nice an cool. Surely this cant be right as it will wear the belt out wont it? And I have just replaced the belt....:(
Cheers

[Blknight.aus]

its got a clutch in it...

the outside of the pully is still turning but the center mechanism has stopped, think of it as putting your foot on the clutch in a manual at a set of lights but leaving the gearbox in gear. If you sieze the compressor and the clutch cuts in one of 2 things happens..


1. it tears the clutch mechanism apart and you get a noise that sounds something like half a dozen tuning forks being chucked into a blender but not as musical. most people shut the engine down pretty quickly when that happens.

2. it stops, at very low engine power levels it might stall the engine. if it doesnt the belt slips on either the crank drive pully or the aircon pump pully. Lots of smoke ensues untill the belt snaps. most people pull over and the engine stalls at the idle speed or it gets shut off and the driver runs because they think the things about to catch fire.

[Gnasher]

Thanks mate, guess I'll leave the AC switched on, cold though it is at the moment, until i can get the unit replaced.

[Blknight.aus]

Bring it round for a look see if you like....

[isuzurover]

When you say the belt is "dragging" across the pulley, what do you mean exactly??? A squealing sound? I suspect your clutch mechanism/bearings might be dodgy, hence the noise. However if your clutch was siezed, you would likely just keep driving the compressor until something burst. A properly tight serpentine belt can impart a lot of force.

Even with the AC on your compressor cycles on and off as needed.

[Davehoos]

denso compressor[?]
destroyed the nose and bearing.?
dont go too far.you can replace the nose but a compressor is cheeper.
the rubber type clutch plate gap must be correct.very rare but conventional steel strap plates come with chinese copies.

sanden TR type dont drive if the gap is too big or the volage to low.

A/C should stay on all year.you turn on the heater.just like in the shower.

[Gnasher]

Izusurover - just had new water pump, viscous unit, and belt done, but when i got home and had little look, the compressor pulley wasnt going round, the belt looked like it was just slipping around it. When i turned the AC on from inside the car, the pully was spinning.
Is the pulley in 2 pieces? inner and outer? RAVE doesnt really show the pulley in that detail. Maybe I need to see if the part that the belt runs on, the inner bit is actually turning, and not the outer face, bit hard to see, and im not sticking my oinkies in there.
Cheers

[isuzurover]

Izusurover - just had new water pump, viscous unit, and belt done, but when i got home and had little look, the compressor pulley wasnt going round, the belt looked like it was just slipping around it. When i turned the AC on from inside the car, the pully was spinning.
Is the pulley in 2 pieces? inner and outer? RAVE doesnt really show the pulley in that detail. Maybe I need to see if the part that the belt runs on, the inner bit is actually turning, and not the outer face, bit hard to see, and im not sticking my oinkies in there.
Cheers

Yes it is 2 - actually 3 pieces.

The pulley which spins free when the AC is off. The clutch (on the front) - which only spins when the compressor is engaged.

Here is a non serpentine version, but you get the idea - the pulley, middle bit is able to turn freely, but the outer part only turns when the AC is working (and even then will cycle on and off).
http://clutchwalletss.com/wp-content/uploads/2011/05/Ac-Compressor-Clutch.jpg

Unless it is making hideous noises then it sounds like it is working fine.

[Gnasher]

Thanks mate, you are spot on, I can just see the outer ring spinning when the AC is off, (clutch dis-engaged), its hard to spot at first with a nice new shiny belt on, as you can only just see the rim moving, and everything else has stopped.

Phew!... panic over

Cheers