Date: Sun, 2 Sep 2007 09:38:51 +0100
From: "moray" <mtb_hyphen_rulesnospamail.co.uk>
Subject: Re: [XP] Sporadic aircon


"Colin Stamp" <col.dustbinnospamp.plus.com> wrote in message news:pqhjd35bjhk0tgu6svmgu38u8spbcfs61onospamcom... > Hi all, > > I have a 2001 Saab 9-3 Aero with dodgy aircon... > > Every now and then, the cooling stops working for a few minutes and I > get air at outside temp from the vents and misting windows until it > spontaneously fixes itself. The problem seems to get much worse in hot > weather, though it could just be that I notice it more in hot > weather... > > I had the system "serviced" at my local Saab dealer but, if anything, > the problem is now worse. > > I tried bodging in some temporary instruments in an effort to work out > what's going wrong, but I need some help interpreting the results. > First, I tried wiring the pressure sensor on the condenser to a > multimeter on the dash. If the readings are to be trusted, then I get > the following pressures :- > > Before startup (system cold) - 7.3 bar > Maximum whilst driving - 14.4 bar > During failure whilst driving - 7.1 bar > > To my untrained eye, it seemed like the compressor wasn't running > whilst the system was in the failed state, so it was a control system > fault rather than a refrigeration problem. To confirm, I taped an LED > to the dash and wired it across the compressor relay coil. > Of course once the LED was in, about a week went past before the > system failed again. Finally today, half an hour of 1st gear at idle > speed through Woburn safari park did the trick. The LED tells me that > the coil is actually powered continuously through a failure, which > wasn't what I was expecting. > > So, I guess that leaves me with two possibilities - either it's the > Compressor relay/wiring/clutch, or there is a problem with the > refrigeration system itself. > > I'm not sure whether the pressure readings actually rule out a > refrigeration problem or not. Could it be that low refrigerant would > cause it, for instance? > > I think I need all the help I can get on this one... Most likely a knackered clutch on the compressor. Connect a test lamp from the clutch power wires on the compressor, and see if it's still getting power when the system stops working.

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