A/C wiring diagrams

BRETT WEEKS

MEMBER
2001 CHEVROLET 2500
6.0L
V8
4WD
AUTOMATIC
265,000 MILES

New compressor, new high and low pressure switches, new EVAP, new accumulator, new condenser, new PCM, new relay, good control module inside. So, after testing the relay pins in the fuse box, I have constant hot (30), hot with ign (86), a ground at pin 87, but I'm not getting the "turn on" signal at 85. If I jump from 86 to 87, the A/C works but the compressor doesn't cycle off. With everything being new, I feel like it has to be a broken wire. Problem is, I don't know. A) on the relay, which wire is connect to pin 85, and is it connected to the inside control module or the PCM? B) what color is it? I have the proper testing tools, but don't know which wire(s) I'm looking for to test.

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3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

87 is not a ground. It goes from the relay to the clutch.

I attached the diagram for you of the compressor circuit. 30 and 87 are the load circuit. It will complete when the ECM grounds the control side. The ECM will ground it when it gets the correct signal from the pressure switches.

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check the switches listed in the diagram. You should have 12 volts at all 3 switches with the key on. The low-pressure switch is normally open and closes when 20 pounds or greater is in the freon system. The high side switches are normally closed and only open when the high side exceeds 375.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Roy

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Sunday, June 27th, 2021 AT 2:22 PM

BRETT WEEKS

MEMBER
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Thanks for that. So, here's an update that has me both upset and happy at the same time. You mentioned specific voltage, so I went to test the voltage. I've tested for signal previously, but not how much voltage. Okay, so I reached behind the compressor, to once again unplug the high pressure switch and test the pigtail connector, and the darn thing fell apart in my hand. So, I got a new one, put it on, and BOOM! My A/C is once again working as it should. Upset at how much money I spent replacing parts, but happy because my A/C is working, and has all brand new parts. Thanks for the help.

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Sunday, June 27th, 2021 AT 3:58 PM

ASEMASTER6371