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Old 07-19-2003, 07:27 PM
psfred psfred is offline
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Hard to tell right off the bat, but with the windows open, blower on high, engine at 2000 rpm, you should have about 35 psi on the low side and somewhere between 250 and 350 psi on the high side, depending on ambient temp and whether or not the aux fan is running.

Low side temps will drop much lower than that when the expansion valve closes, though, but shouldn't rise much higher.

For R12, the pressure and the temp in degrees F is the same on the low side, you never want it below 32 psi with the expansion valve open or the evaporator will freeze. It will drop to 15" of vac sometimes, with the expansion valve closed, before the evaporator temp switch cuts the compressor off.

pressures over 40 indicate a failure of the expansion valve or air in the system, usually.

Very low low side pressure (15" vac all the time, suction line not cold) indicates low charge. High side will also be well under 200 psi in this case, also. If the high side is 350 to 450, the expansion valve is plugged or stuck shut.

I didn't look these up, so someone with better information can correct me if I'm wrong!


1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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