AC Compressor Stopped Engaging

[shultzee13]

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.

[JohnHere]

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.

[shultzee13]

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?

[shultzee13]

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.

[71403]

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.

[shultzee13]

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.

[71403]

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.

[shultzee13]

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

[shultzee13]

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.

[71403]

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