Air Conditioner Wont stop running

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Big G

Big G

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Hi Everyone,

I am new to the forum and I am hoping you can help me. I have a 99 Burb with the Big Block and my air conditioner will not shut off, the A/C continues to run even with the fan and A/C switch turned off on the dash. I just bought a new A/C controller from RockAuto and replaced the Compressor/ clutch assembly as well and it just continues to run. If I disconnect the low and high pressure switches the compressor still is engaged, the only way for me to turn it off is to pull the A/C relay.

I am at my wits end and hopefully someone can shed some light on what I am missing.
 
delta_p

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is it a bad relay? What about with the relay out and check the control side ground to the VCM, can you affect it with the high pressure cutout switch disconnected, is it grounded all the time?
 
east302

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Agreed, it could be a constant ground. The VCM may not be disabling the ground for the relay when the a/c is off. Or possibly a short to ground. Maybe pull the relay and test for voltage grounding to relay cavity B6. It shouldn’t show voltage with a/c off. Also make sure the defrost isn’t selected.

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VCM connector C3 pinout:

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Big G

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Thanks for sending me the wiring diagrams they were very helpful, I finally got around to looking at my A/C problem and have checked everything you suggested and come to the conclusion that I have a bad computer. Your thoughts??? I pulled out the 32 pin connector and checked for continuity between pin 1 and the B6 terminal inside the relay cavity with my DVM and it shows 0.05 ohms of resistance. When you turn on the A/C button I do have power at pin 25 as I should, then I pulled both the A/C and the IGN E fuse and then checked the B6 relay cavity and still show it to be grounded. What and I missing???

I don't mind buying a computer if needed just dont want to buy one and it not solve my problem. Also if I do have to buy one then I might as well get it tuned at the same time, Any recommendations???



Thanks

Garrett
 
Busted Knuckle

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The odds its the computer are extremely low. Could be a pinched wire. I can't recall ever finding a bad computer, but have seen some thrown at the problem. Its easy to follow the diagram, but hard to find test points you can access.
 
SAATR

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Disconnect the 32 pin connector from the VCM and check continuity between relay terminal B6 and engine or chassis ground. If you have continuity to ground, then you have a short between that wire and ground somewhere along the harness. If that turns out to be the case, then you'll need to inspect the harness from the VCM out to the relay block to find where your short is located.
 
Big G

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Thanks for the quick reply. I just pulled the 32 pin connector from the VCM again and checked for continuity between B6 relay and engine ground then body ground in multiple areas and come up infinity.. No continuity. Again I checked it between B6 and pin 1 I show good continuity or resistance of 0.05 again. I am still at a total loss.
 
SAATR

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Big G said:
Thanks for the quick reply. I just pulled the 32 pin connector from the VCM again and checked for continuity between B6 relay and engine ground then body ground in multiple areas and come up infinity.. No continuity. Again I checked it between B6 and pin 1 I show good continuity or resistance of 0.05 again. I am still at a total loss.
Click to expand...

So the relay wiring is sound. Does pin 25 energize and de-energize when the AC button is cycled?
 
SAATR

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Then it sounds like you have a VCM issue. A control output without the corresponding trigger input would say the module or programming is faulty. You could probably test with a junkyard ECM of similar YMM for reasonably cheap.

Just to be sure, if you remove the wire from pin 25 (AC request signal) it does still run the compressor?
 
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