Sounds like Pressure switch is broken or working - Saab 9000 Bulletin Board - Saabnet.com
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Sounds like Pressure switch is broken or working
Posted by Robert Kaplan (more from Robert Kaplan) on Sat, 20 Apr 2002 18:53:20
In Reply to: Air Con problem, Terry Pugh, Sat, 20 Apr 2002 08:48:09
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The high pressure switch is preventing your compressor from coming on. When it's not that hot, high side pressure is within acceptable range. When it gets hot out, a/c pressures rise along with temperature. The rise in pressure trips the overpressure switch.
Usually, the symptoms you describe result from an overcharge. However, 950g is the correct quantity for my 93 cs. Assuming all is the same with your car, then the pressure switch is broken, or something is driving your pressures too high.
High side pressure is very dependent on effective heat transfer from the condensor in front of the radiator. The cooling fan behind the radiator comes on at 220 psi and goes off at around 175 psi. The fan in front of the condensor runs any time the compressor is working.
Since you have the correct quantity of refrigerant, my next guess would be an obstruction in the high side, which would cause high side pressures to skyrocket. Likewise, any kind of fan failure or crud on the condensor can cause high pressure to soar. If you have never had a compressor failure, I would be looking at the expansion valve. Watch for excessive high side pressure and very low low-side pressure. Expansion valve failure can cause the low side to go into vacuum.
Want to confirm high pressure is causing your problem? Wait until it does't work and then spray the grill with a garden hose. The air will come on in about 10 seconds.
posted by 24.50.5...
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