Automotive Air Conditioning Information Forum

98 Suburban 2WD 5.7L

Initial problem - AC stopped cooling at Idle. When driving was cold.
Saturday stopped cooling all together. Compressor not engaging. Have checked all fuses and relays and all are good. I have power to everything. Hi and low pressure switches have both been replaced.
Compressor will turn when jumpered to battery. It will turn by hand.

Low side port has a lot pressure build up. It's actually way to high right now.

Brand new AC delco compressor - 8 months old.

Very warm in Texas.

Low-side and high-side pressures would help with a diagnosis, but I suspect that most of the refrigerant has leaked out someplace.

You'll need to charge it back up with enough R-134a containing UV dye to get the compressor operating again, run it for a few days (if possible), and then do a visual leak-check for the dye and/or use a refrigerant sniffer. Look for any oily spots on the system components that might indicate a leak, test the vent air with the sniffer, and check the condensate drain tube and as many components as you can for the presence of dye.

The low-side reading is way high....like almost 100 pounds in the red on the gauge and you are saying to ADD more Freon?

with the suburban on or off...I hook up the gauge to the low side and it immediately jumps to 125 way in the red.

The engine computer controls the a/c clutch on that truck, there's many things non-a/c related that will cause it to not engage the compressor. Assuming gauge on death can is ballpark correct you have enough pressure to satisfy the cycling and low pressure switches - if it's not engaging it's an electrical or other problem.

Wiring diagrams and/or a trip to a shop with a real scan tool would be the next step.

Local shop just told me on the phone that something that commands the ac clutch to come on is … not commanding it. I have already installed a brand new AC relay.... but I guess it could be bad. I'll have to replace it again and see if that does the trick.
Other than that..... I have no idea what else commands the AC compressor clutch to engage. I know when I jumped it straight to battery it did come on.

It's a lot harder without a real scan tool but here's a few basic steps

1. Verify the two 10A fuses in the underhood fuse panel for the compressor clutch and clutch relay supply are good. ("Ign E" and "A/C Comp")
2. With a/c requested from the HVAC control, verify +12 volts at high pressure cutout switch, lt green wire. That proves out the HVAC control requesting a/c.
2a. If present reconnect switch and verify +12 on dk grn / wht wire by backprobing the connector. That proves out the high pressure switch

Have seen the comp relay installed backwards.... some cars it's possible due to symmetric pin config.

Thank you for your help. I will get out the test light the minute i get home and report back.

Having to use a new after market all white connector harness and don’t have original connector anymore. Do you know if the green with white stripe (power) is A OR B on connector. I googled a pic but cannot tell which one for sure.

It's a switch, no polarity, so doesn't matter A vs B.