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Dear all, I'm trying to diagnose a problem with the a/c on my '95 900SE and, not fulling understanding how the a/c works, would appreciate any advice.
Up to last week, the a/c has worked fine, albeit with a whine when the compressor is running. This is only audible at idle / low revs and I attributed it to the expansion valve.
Last week, things changed. The performance of the a/c in terms of cooling is still fine - however, the following happened simultaneously:
1) The whine, which has been constant since I've had the car (last 14,000 miles) suddenly got noticeably louder and can now be heard most of the time when driving with the compressor running.
2) The compressor no longer cycles even on cool evenings - it stays on all the time. I have a separate fault in that the anti-frost switch doesn't seem to work (compressor has overheated on a couple of hot days and cut-out). Therefore, to prevent this happening again, I'm manually cycling using the econ button.
3) Every minute or so there is a soft 'clunk' from somewhere in the dash. It's not audible outside the car or under the hood. At the same time that this happens, a) the engine revs drop (only noticeable at idle) as if there's a sudden load on the compressor, b) the engine fan kicks in for about 5 seconds and c) looking through the site glass, something is obviously happening to the pressure as I can see bubbles for a few seconds. After this it returns to normal - no bubbles.
I'm reckoning that a faulty expansion valve is causing a sudden pressure difference, putting a load on the compressor. The rest of the time, the same fault isn't allowing the a/c pressure to build up sufficiently to switch off the compressor.
This make sense?
The only thing I can't work out is why the engine fan kicks in at the same time.
Given my experience with dealers I'd much rather tell them what to change than have them diagnose it so, before I book, would appreciate any advice.
Many thanks,
Oliver
'Jacuzzi'
1995 900 SE
88,000km
posted by 210.7.96...
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