After replacing the A/C compressor and condenser, still not cooling properly?

2002 GMC SIERRA
257,850 MILES • 5.3L • V8 • 2WD • MANUAL
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RB95
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Hello! I have the truck listed above 1500 with a 5 speed. I recently replaced my compressor and condenser, and I am still having cooling issues. Compressor runs when jumped at the relay. All sensors are bypassed. Freon is adequate.

Probing AC Relay pin 85 shows an Intermittent Ground from the PCM. It works when i drive down the highway. It works when i first crank the engine. But when i put the truck in gear and roll it, the ground immediately goes away. Then the compressor will kick on, drop RPMs, then immediately kick off. Over and over.

With the multimeter on my hood, I can watch the GND come in and out from pin 85
Aug 11, 2023 at 1:05 AM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.
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STRAILER
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It sounds like the PCM, or the HVAC controller is bad, you might what to do a CAN scan to see what codes come up. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here are the AC system and compressor wiring diagrams so you can see how the system works. Check out the images (below). Please let us know what happens.
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Aug 11, 2023 at 2:51 PM
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RB95
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That's all great information! I'm not seeing any codes with an odb reader. I just bought an ODBLink LX Bluetooth scanner. Do you know if the CAN system can be read using LSDroid or similar app?
Aug 11, 2023 at 11:00 PM
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STRAILER
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You need to look at their product information, but I don't think so.
Aug 12, 2023 at 10:09 AM
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RB95
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So, I cleaned out the ground on the harness below the alternator - using your diagram. It seemed to help! I reset the PCM by disconnecting the battery and grounding the power cable. I tested resistance from AC relay pin 85 and pin 43 on red connector of PCM. Sat 0 ohms. Cleaned out dust from the back of the PCM connectors.

Is there any chance that an old battery or alternator could cause this? I have an Optima with accessories on it. My headlights are showing weird symptoms. Running aftermarket harness. +12v at each plug. HIDs will not work at all. Halogen comes on one at a time and dim constantly. Any info helps. Thank you
Aug 13, 2023 at 9:08 PM
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STRAILER
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It is possible if the system is low on voltage, it will not pull the A/C clutch in. With the engine running are you getting about 14 volts? Please go over this guide:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Please go over this guide and get back to us.
Aug 14, 2023 at 12:26 PM