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1985-1998 [Subscribe to Daily Digest] |
There is no such thing as a correct pressure because there are so many variables. That said, there are objective standards which I use to evaluate pressures. The high side pressure will vary substantially depending on outside air temperature and humidity. The low side pressure will fluxuate somewhat depending on outside air temperature, but will stay within a much smaller operating range.
I have charged my 9000's to a multiple of 2.8. I arrived at that mulitple through a couple of years of trial and error by charging while monitoring the vent temps to look for a bottom temperature out of the vents. Lately I have been thinking this multiple may be too high and I might try 2.7 instead next time.
The way this works is to set the car running at exactly 1500 rpms. Next, measure the outside air temperature a few inches in front of the condensor (Let's use 90F as an example). You then multiply that number by 2.8 to produce an ideal high side number (90 x 2.8 = 252). You then charge until the high side pressure reaches 252 psi with the fans running. Only then do you pay any real attention to the low side. I would look for a low side range at 90F of between 18 and 35 psi @1500 rpms. All with the fans running.
I figured that the pressures you mentioned earlier were at idle based on the low side reading of 40 psi. With the car running at 1500 rpms, not only will the high side increase, but the low side will also decrease. It's the pressure differential that produces cooling. If those pressures were not at idle, you may have air in the system.
If your car is not cooling, I would first look for a problem with the air blend. The pressures you mentioned are close enough to normal that you should be getting some cooling. The only way to positively rule out a blend problem is to squeeze one of the heater core hoses between 2 blocks of wood with vice grips. If that's not the problem, you may have to take apart the system to flush it and then pull a vacuum to improve cooling. A new receiver/drier would also be indicated if you go that route. Excess oil could be a problem, but the only way to get it out is to open the system and flush it.
posted by 64.222.103...
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