A/C no power from interior

MECHANICALDAD

MEMBER
2000 CHEVROLET SUBURBAN
0.5L
V8
4WD
AUTOMATIC
240,000 MILES

I had my engine rebuilt. When I got it back the A/C will not come on (of course they did nothing).
Pressure switch seems functional. If I override the fuse/switch at the PCM the A/C works fine except drains the battery when I forget to turn it off!
I tried a different climate control board and no change. This has the auto temperature climate control board with rear air. May not be related but the rear defrost button next to the A/C button is not functioning either. To search the A/C wire can you give me the diagram? Also, to check the control board out of the vehicle with another harness how would I test the switch. Awful lot of questions here. Thanks

7 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

What switch did you bypass and how? You may have damaged the PCM is you powered something wrong.

I attached a wiring diagram for you to view.

The PCM will ground the control side of the AC relay once it gets the correct signal from both the low-pressure switch and the high-pressure switch. You need to verify they are working correctly.

The high switch is normally closed and opens at 375 lbs.

The low-pressure switch is normally open and closes at 20 lbs of Freon pressure.

Roy

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Sunday, August 5th, 2018 AT 11:59 PM

MECHANICALDAD

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6 POSTS

I just added a switch in place of the 8567 relay fuse.

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Wednesday, August 8th, 2018 AT 6:36 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

Did you just jump 30 and 87 terminals? If you did, then you have no protection if the system pressures are out of spec.

Roy

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Wednesday, August 8th, 2018 AT 8:15 AM

MECHANICALDAD

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6 POSTS

Yes that is what I did however, I did have a garage look at the specs prior to doing that. They also could not get power to the 30 and 87 terminals with the dash switch. I thought I could try to trace the wire if maybe the garage who replaced the engine damaged it somehow. I assume I need to check elsewhere first to see if when I activate the switch on the dash? I had a test light on the 30/87 terminals but thinking it looks for power somewhere else before it activates that terminal? Yes/no?

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Friday, August 10th, 2018 AT 7:18 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

Okay.

The power to 30 comes from the fuse block only, not from anywhere else. 87 becomes hot only when the control side of the relay grounds.

You need another shop that knows how a relay works and can find the issue for you. It sounds like your guy does not know how the system works as well as a relay.

Roy