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variable compressors and low side pressures

ron7000 on Wed June 27, 2012 11:25 AM User is offline

Year: 2002
Make: Chevy
Model: Camaro
Engine Size: 5.7L
Refrigerant Type: R134a
Ambient Temp: 98
Pressure Low: 45
Pressure High: 250
Country of Origin: United States

2 questions,

- how can i tell if an automotive ac compressor is a variable displacement type compressor? For 2002 and later GM cars and trucks what are they?

- I'm an original owner of a 2002 camaro, the AC has never been touched except by me last year when I added less than 1/2 can of r134a using a manifold gauge set and a small 12 ounce can of r134a. At that time i thought the air was not as cold as it should be and over the last few years i was not satisfied with the AC performance. The car has a big windshield, no tint on the door windows, and has t-tops. If i don't have the sun shades in the t-tops you roast. So the cabin gets a lot of heat input from the sun so that might be a factor. The vents blow fairly well, as well as they did when i got the car new and with blower speed on high it's noisy.
Unfortunately I don't remember low side pressures before adding r134a last year, but i don't remember the compressor ever cycling off.
This past week we had some 95-100F humid days and I had fairly cold air out the vents, measured it with a fluke and showed 50-55F at the vents, and passengers said they thought it was ice cold. Decided to check the pressures with my gauges that day and at idle the high side was 250psi or higher, enough to kick the radiator fans on high speed. Low side pressures were 45-55 psi if i remember correctly. Let the car sit for an hour and around 8pm when sun wasn't hitting my driveway checked again and engine bay still fairly hot. Static pressure read around 130-140 psi if i remember correctly. Turned AC on and high side went up over 200 psi quickly and radiator fans kicked on high speed. Low side pressure came down quickly to around 80psi then slowly down to 60 to 50 psi. Is this normal given the hot ambient temps?
I would like to know what normal low side pressures are supposed to be? With everything functioning correctly, does hotter ambient temps and heat load on the AC system raise low side pressures? Or should I always see 25-35 psi low side pressure?

GM Tech on Wed June 27, 2012 12:22 PM User is offline

How do you tell--- memorize them like I did.....A V-8 camaro uses a V-7 (7 cylinder) variable (thus the "V" designator) compressor --- a 3.8l engine uses a V-5 (again a variable 5 cylinder compressor (V-designator)

Low side pressur is always 25-35 if ambient is say 80 degf or less-- it means compressor may be at any amount of stroke to maintain that suction pressure--- if suction pressure rises above 35 psi - then compressor is definitely at full stroke- much like a fixede displacement pump. Keep in mind that variable compressors never cycle for evap freeze control-- they destroke instead-- If a variable is "cycling" , then it has high pressure issues-- as in no cooling fan..

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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