aircon compressor pump stops turning when off

[markdav]

Hi,

Is it normal for the aircon compressor pump to stop turning when the aircon is off? During the first few seconds after starting or if I switch the aircon off, the belt travels round all the pulleys correctly but the aircon pump pulley does not turn. As soon as I turn the aircon on again, it starts to move. No problems with cooling, heating etc. This just does not seem right (belt wear, friction heat, etc would result).

I heard that the aircon has a clutch mechanism built in - maybe this is faulty?

Car details - 2000 Boxster 2.7, USA, manual transmission.

Thanks, Mark.

[0586slb]

You have described the exact functionallity as designed. The AC compressor does have a clutch, this, as you say, engages only when there is an AC demand - i.e. when the AC is switched on. It looks strange when you are viewing the running engine, but the outer pulley of the AC is spinning, but the clutch plate and therefore the input shaft of the AC does not turn until the AC is engaged.

[markdav]

Thanks. In my case, the pulley itself stops spinning - the rubber belt is travelling over a stalled pulley. I first noticed this because my engine revs would momentarily drop when the aircon was switched off (normally assume a slight increase in revs since the workload has been removed until the idle adjustment kicks in).

Sounds like my clutch is sticking between being in and out and is trapping the pulley. Are these servicable or would a touch of oil help? Hate to pay $900 for a new unit that otherwise works perfectly.

[0586slb]

Mark,

I've just re-read both of your posts and if the pulley is being stalled, the polyrib belt will not last very long at all.

What puzzles me is that the pulley part of the AC compressor drive is in its own bearing race, so will not free off just because the AC clutch is engaged and giving a slight axial pressure. Please verify the pulley itself is stalling by popping a small spot of paint right on the edge. The clutch plate goes pretty much right to the edge of the pully, so may appear as if the whole pulley has stalled at first glance. Are you viewing the pulley from underneath the vehicle or through the access panel behind the seats?

Best, Christopher

[markdav]

Hi Christopher

Thanks again for your attention. (BTW, nice result at the weekend! We get very limited coverage of the Premier League living here in Seattle...). I digress!

I can confirm that the whole pulley stops when the aircon is off. I'll open her up again tonight and take a short video.

I notice 3 bolts at the front of the pulley - is it worth taking those off and checking behind the pulley?

I have searched RennTech and PPBB and this fault does seem to be unique.

Thanks again, Mark.

[wvicary]

Don't take anything apart yet..... take a vid of what your on about first so we can really see what your trying to say.

[markdav]

Sorry for the delay. As usual, bring a camera anywhere near a fault and it stops being faulty! Ugh!

Prior to this issue, I had a water pump meltdown resulting in gou all over the belt and pullies - may be that this has freed up now. The revs are behaving as expected now (slight decrease when aircon turned on vs. slight increase that I was seeing before) and the pulley is moving freely.

Will update if this goes bad again.

Many thanks for your help - Mark.