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Have a problem where the compressor on my 2000 Silverado…

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Have a problem where the...
Have a problem where the compressor on my 2000 Silverado won't engage. Took it to a a/c shop and they did some diagnostics on it and said my control head is bad. They said it isn't sending a signal to the pcm to engage the compressor. The question I have though, is that the compressor wouldn't engage even if I jumped the 87 and 30 relay socket. I thought that was a direct circuit.
Submitted: 2 years ago.Category: Chevy
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Answered in 5 minutes by:
1/28/2016
Chevy Mechanic: Dan, Technician replied 2 years ago
Dan
Dan, Technician
Category: Chevy
Satisfied Customers: 25,965
Experience: Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Hello, my name is***** if you jump pin 87 to pin 30 that should force on compressor. Does it?

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Customer reply replied 2 years ago
No it doesn't. They checked all the wiring and they said the control head isn't sending a signal to the pcm. They said all the wiring under the hood is good, and the compressor engages if they jump it straight to the battery.
Chevy Mechanic: Dan, Technician replied 2 years ago

Pin 30 should have voltage at all times. If so then replace the dark green wire that goes between fuse box and compressor. Plain and simple compressor should turn on when jumping pins so they either do not know what they are talking about or you have two separate issues. Let me know how it goes or if you have more questions. Here is a wiring diagram of system. Thanks.

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https://www.dropbox.com/s/asi54gt9ihd7ydj/compressor.pdf?dl=0

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Customer reply replied 2 years ago
They did hook a scanner up to the truck, and that's how they found out the pcm wasn't getting a signal from the control head. Now when I jumped the terminals, I used a paper clip. Maybe I should've used a wire.
Chevy Mechanic: Dan, Technician replied 2 years ago

A paperclip would work fine so that shouldn't be the issue. I'd start by figuring out why compressor doesn't turn on as described above and if you still have issue test wiring between controller and PCM, if good then replace PCM. It definitely sounds like you have a broken dark green wire as of now but you need do above tests. Let me know if you have questions or run into questions, you can reply to this answer at any time without additional fees. Thanks.

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Customer reply replied 2 years ago
Before the a/c quit it was intermittent. It would work some days, and some days it wouldn't. Usually if you left it on high fan it would keep working, but if you put it on low, the compressor would cycle then stop all together. We thought the clutch was going out, so we changed that, and it still didn't fix it.
Chevy Mechanic: Dan, Technician replied 2 years ago

Just going to have to do the tests and go from there, without testing it could be too many possible options. But if you jumped relay correctly we know one issue can only be wiring, connection, or blown fuse. Let me know if you have questions, thanks.

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Customer reply replied 2 years ago
Should I check the abs fuses. My friend said he has a similar problem on a Pontiac Grand Prix and it was a blown abs fuse. Is this circuit shared on these trucks?
Chevy Mechanic: Dan, Technician replied 2 years ago

No, the abs fuse wouldn't cause this. Only fuse that would stop pin 30 from having voltage is the 10 amp AC fuse. Let me know if you have questions, thanks

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Customer reply replied 2 years ago
Just got back from the a/c shop again. They checked everything again, and they said everything is getting voltage. They said since the control head isn't sending a signal to the pcm, that the pcm won't send a ground to the compressor. I did buy some 18 gauge green wire at AutoZone. I found a junkyard with a low mileage control head since they don't make new ones anymore. I'm picking it up tomorrow. I agree with you about the wiring from the relay to the clutch, but I'll see what happens when I swap the a/c controls.
Chevy Mechanic: Dan, Technician replied 2 years ago

Let me know how it goes or if you run into questions. Thanks.

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Customer reply replied 2 years ago
Found a break in the wire near the clutch wire pigtail. Now the compressor engages when I jump pins 30 and 87. The ac control head is still bad though, but I found that out when they did the diagnostics. So apparently I had 2 problems going on. 45 psi low 225 high when the truck is warmed up. The control head comes in this weekend. I'll let you know how it goes.
Chevy Mechanic: Dan, Technician replied 2 years ago

Good to hear the wiring problem was found. It does sound like control head should now take care of the problem. Let me know how it goes, thanks.

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Customer reply replied 2 years ago
Got the new control head installed and the compressor still wouldn't turn on. Crawled under the truck and noticed the mechanic forgot to install the high pressure switch on the new compressor. Found the harness dangling by the oil pan. He's going to evacuate the system and install a switch this week. I'm running it with a paper clip right now. I needed a new control head anyway. Half the bulbs were burned out in the old unit, and I didn't feel like soldering new bulbs in. Got a refurbished one cheap on eBay.
Chevy Mechanic: Dan, Technician replied 2 years ago

Good to hear things are being taken care of. Let me know how it turns out or if you run into more questions. Thanks.

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