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2004 gmc envoy_sle_xl
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Discussion Starter · #1 ·
Hello all, 2004 Envoy Xl owner, I wanted to know if anyone knows what the pressures should be for a properly operating A/C system. My low pressure is high I think at between 50-55, and my high pressures are low around 140-150, and the needle is bouncing. Outside air temp around 80°, and cabin temp doesn't go any lower than 60°. I'm thinking my compressor is going out.

Thanks in advance.
 

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2002 chevy trailblazer_lt
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Based on this data from a service manual your low side looks about right for the 80° ambient but as you say, the high side seems a bit low. What was your fan speed at, normal idle speed??

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edit to add chart headers...

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Discussion Starter · #4 ·
TJBAKER... Would you be able to send me that whole chart? I really appreciate it
 

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Yes sorry, engine fan was not on high.

I had figured that but thought I would ask anyway. Did you happen to measure the discharge temp at the vents?? Is the accumulator cold?

While driving in similar ambient temps today my high side ran 140 or so but there is no comparison for moving vs stationary pressures...

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Discussion Starter · #9 ·
Thanks for the info, the air temperature at the center front vent was 60° at its coldest, that was with the car sitting, at idle.
 

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2004 chevy trailblazer_ls
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Make sure you have the proper charge in the A/C. For SWB it's 29.6 oz, EXT 32 oz. (check the label under the hood). if you can, vacuum it down to 30" for 30 min. to an hour, then add the charge.
 

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PS- if you don't have the proper charge, the pressures won't be correct either.
 

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Discussion Starter · #12 ·
Here's a picture of my gauges this morning. The charge amount should be pretty close. It was basically empty of freon so I put 3 - 12oz cans in it. Like I stated before, I'm thinking my compressor is going out.
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IMG_20210714_095733152_HDR.jpg
 

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Should have mentioned, pull the orifice tube or put a new one in it. If there’s debris on the tube you may need a compressor.
I don’t think the hi side pressure is that bad, lo side too high.
 

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Just a couple of points....

Find an "Intelligent" or "Smart" expansion valve.they really make a big difference ..... I have no idea how ... but they make a system really wake up.

All testing policies... in all the classes I took for R134a --- told us to run the blower(s) at medium speed, use the center-most discharge vents and instead of getting frantic about pressures, there's a much easier way to gauge system pressure.

After the engine has idled for at least 15 minutes, check the temperature of the compressor.

The ambient air temp and humidity, cooling fan RPM and efficiency, ram airflow and the cleanliness of the condenser can grossly mess with pressures--- especially on a system that has some miles.

Reach down and gingerly touch it. "Gingerly" is the operative here.

The compressor temp should be somewhat high enough that you don't want to hold it any longer, but it's not blistering your hand.

☆ If it's cool or even cold ... it's under charged.​
☆ If it's really too hot to touch or your fingertips sizzle --- it's overcharged.​

Actually ... test the temp with a contactless infrared thermometer..... it should read 160°-170° Fahrenheit.

Really .... all it boiled down to was compressor temperatures.

Don't bother feeling the lines or the receiver/drier. Everything else is a strawman.

You can blow this technique all to hell if you can accurately charge the system with a charging station. Other than using one of those, use the compressor temp technique.
 
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