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High low side pressure

haanjamin on Wed July 20, 2011 9:49 PM User is offline

Year: 1995
Make: Pontiac
Model: Trans Am
Engine Size: 5.7
Refrigerant Type: R134a
Ambient Temp: 95
Pressure Low: 80
Pressure High: 125
Country of Origin: United States

I just vacuumed the system and started to charge it. A full charge is 32 oz. After getting only ~8 oz in with the compressor running, the low side was 80 psi and high side was 125. This is with the car at idle. That's all I could get out of the can because the low side pressure is high. Blower motor on high, max AC, and radiator fans were running. The pressures make it seem like something is wrong, like not enough pressure drop through the expansion valve.

Some searching brought up a couple similar cases which were fixed by getting airflow over the condenser but both my electric fans are running. I'd like to get some opinions on what might be the problem and best course of action. Thanks

Edited: Wed July 20, 2011 at 10:09 PM by haanjamin

bohica2xo on Wed July 20, 2011 10:23 PM User is offline

Your low side coupler is not depressing the schrader valve properly. You are reading the pressure in the hose. The schrader acts like a check valve - you can push refrigerant past it, but not very quickly.

Try manipulating the coupler. Pull the lock ring back, and push it deeper into the connector on the car.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

haanjamin on Thu July 21, 2011 7:50 AM User is offline

I believe the gauges are reading correctly because it showed a higher static pressure (~100psi) and the pressures were changing slightly with the compressor running (75-80 psi). Just to be sure, I'll try what you said. Thanks.

iceman2555 on Thu July 21, 2011 6:00 PM User is offlineView users profile

Get more refrigerant into the system. There is not a sufficient amount to make the system perform. To adequately diagnosis a system the system must be FULLY charged. The best method is to use the correct charge procedure to introduce all the refrigerant into the system at once. Adding cans to a perceived operational pressure is not an acceptable method to charge a vehicle.
Try 'warming' the cans during the charge process....not a substitute for a proper procedure but it is a method to 'force' the charge. BE VERY CAREFUL WHEN ADDING REFRIGERANT WITH THIS PROCESS. EXCESSIVE HEAT EQUALS EXCESSIVE CAN PRESSURES AND THE RESULT CAN BE QUITE HARMFUL. Simply place the can into a container of warm water. Insure that the low side charging port of the gauge is 'open' prior to placing the can into the water.

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haanjamin on Thu July 21, 2011 7:32 PM User is offline

I coaxed another 12 oz into the system, took about 30 minutes with the can sitting in a warm bath. Pressures are now 90 low side, 105 high side while spraying cold water on the condenser. Around 100, 120 after the water evaporates. Compressor is running. Go for another 12 oz to get to my 32 oz? Doesn't seem like the compressor is operating correctly.

Edited: Thu July 21, 2011 at 7:38 PM by haanjamin

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