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Discussion Starter · #1 · (Edited)
I've got a mystery on my hands and would appreciate any help troubleshooting my climate control module \ system.

97 GM factory wire. No add-ons
Couple of weeks ago the AC stopped blowing cold but only for a few minutes. Hmmm.
A few days later it would not cool at all. Checked the Freon and it was low.
Went to top it off and could not engage the compressor by jumping the LP switch so I checked the voltage (unplugged), 12v on purple and 0v on pink. Connected the switch and have only millivolts across the pink and purple (switch was closed as expected).

The blower and vents works normally. The engine fan also kicks in normally when the LP is connected.

I was able to engage the clutch by running 12v from the battery to the pink wire on the LP connector. System is now charged but the compressor will not engage without running 12v from the battery.

LP and HP switches tested and are closed while connected to the system.

Checked AC cutout relay and it appears fine. I didn't check continuity but I heard it click, and I swapped it with another relay.

Performed a direct current draw test on the clutch using the battery and it pull a little over 3v when closed

Performed a current draw test from the LP switch and it was in the millivolts. It appears I have volts and no amps.

Pulled the climate control module and checked the purple wire with the LP connector off and got 12v as expected, but I could not do a current test without cutting the purple wire in the harness. Checked again with the LP switch and had millivolts again as expected. I say "expected" because the volts and amps were the same as my under the hood numbers.

I removed environmental control module from the dash and took it apart to see if there was any visual damage. There were 3 diodes in a row that had dusty oxidization like crust around the pins. I cleaned it and reinstalled it in the car.

Started the car and pressed Max AC and the compressor engaged normally. Cycled the power and I'm back where I started. No clutch.

I'm leaning toward the control unit as the problem but that's an expensive crap shoot and I'd like to know if there is any other way a novice with common tools can verify before ordering a new one. I've already tried the diagnostic test and it completed with no codes.

I would think the module would or should only send minimal current to the relay and let it handle the amps but I have not found enough info to track the wiring. Knowing volts and amps would be great but right now even a good schematic would help.

Sorry for the long post. I didn't want to leave out any steps.
 
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