Date: Sat, 01 Sep 2007 21:53:39 +0100
From: Colin Stamp <col.dustbinnospamp.plus.com>
Subject: [XP] Sporadic aircon


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... Cheers, Colin.

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