Date: Sun, 02 Sep 2007 00:06:29 +0100
From: Colin Stamp <>
Subject: Re: [XP] Sporadic aircon

On Sat, 01 Sep 2007 21:27:54 GMT, "Mrcheerful" <> wrote: > >"Colin Stamp" <> 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... >> >> Cheers, >> >> Colin. > >incorrect gas quantity will give over high or over low pressures, either >will turn the system off. get the system vacuumed and properly refilled. > But the system isn't turned off - in the failed state, the compressor relay is pulled in continuously. Also, the pressures seem to tally with the spec for the system. The fan supposedly cuts in on speed 1 at 9 bar and goes to speed 2 at 18 bar. The compressor gets shut down below 2 bar and above 24 bar. According to that, I have a maximum pressure somewhere between the two fan speeds, and a minimum well within spec. The aircon service I had done did purportedly include a re-gas. I suppose they might have botched it... Cheers, Colin.

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