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A/C compressor will not engage?

Tiny
HD1200
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 2,222,222 MILES
At wits end why A/C compressor will not come on. I can jump the relay and compressor will come on. I’ve checked all the fuses and the relay for A/C and they are all good. Also, pressure switches are good. I changed out ac control in cab.
Installed rebuilt PCM.

I evacuated the system and charged with 2 cans Freon but compressed never came on I know if everything is correct compressor should come on after 24 oz of Freon.

About 5 days later I checked the system with gauges and the system was about empty. I noticed that the low side pressure valve was leaking.

My question is, could the Freon I was filling could leak out that much and cause compressor not to come on?

When I evacuated system it held steady at -30 on gauge for an hour. Is it possible you can evacuate, and it shows no leaks but under pressure something faulty like the low side pressure switch it would leak?

What I’m trying to figure out is the problem just the leaking pressure valve or something else could be bad like shorted wire somewhere?
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Wednesday, September 13th, 2023 AT 11:17 AM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

If the leak was from the Schrader valve, it could hold a vacuum because you are attached the valve.

When you recharged the system, what was the static pressure? Also, since you can jump the relay and the compressor turns on, have you confirmed a ground path to the PCM via the relay's primary circuit? Is there power at the compressor when you turn it on? If there is power, then there simply may not be enough freon in the system.

Let me know.

Joe
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Wednesday, September 13th, 2023 AT 6:57 PM
Tiny
HD1200
  • MEMBER
  • 61 POSTS
I can jump relay A/C compressor clicks that’s with ignition on truck not running but when I unplug A/C compressor and test wires, I have ground but no power.
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Thursday, September 14th, 2023 AT 7:04 AM
Tiny
HD1200
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  • 61 POSTS
Does the dark green wire supply power from the A/C 10-amp fuse?
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Thursday, September 14th, 2023 AT 8:19 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

I attached the compressor clutch wiring schematic for you below. Yes, the solid dark green wire is the power supply to the clutch.

If you look at the relay, each of the 4 pins is numbered. Pin 30 should have power at all times. Pin 86 should only have power with the key in the run position. Pin 85 is what provides a ground path to complete the primary side circuit which actuates the secondary. When that happens, the dark green wire should power the compressor clutch.

Let me know if you have checked it that way. Also, here is a link that explains how to test a relay and its circuit:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know.

Joe

See pics below.
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Thursday, September 14th, 2023 AT 6:32 PM
Tiny
HD1200
  • MEMBER
  • 61 POSTS
Okay, I’ll check that and update once done.
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Thursday, September 14th, 2023 AT 7:19 PM
Tiny
HD1200
  • MEMBER
  • 61 POSTS
When I’m doing all the electrical checks should the system be charged? I’m checking it without a charge. With key on engine off A/C button on all A/C fuses good but have no ground from PCM to relay. If system is charged will PCM ground relay? I also noticed the green/white striped wire for PCM ground was pulled out a bit from the black connector underneath engine compartment fuse box.

Please let me know if ac needs to be charged to see if PCM grounds relay.

Also, with key on engine off A/C button pressed I have ground at ac plug on black wire no power on green wire but have ground on green wire.
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Wednesday, September 20th, 2023 AT 8:23 AM
Tiny
HD1200
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  • 61 POSTS
I can jump relay and it clicks.
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Wednesday, September 20th, 2023 AT 8:24 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

When you hear the relay click, does the compressor clutch engage? Also, if it doesn't check off there is power to it when you jump the relay.

Let me know.

Joe
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Thursday, September 21st, 2023 AT 6:15 PM
Tiny
HD1200
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Okay, I’ll check and let you know.

Thanks
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Thursday, September 21st, 2023 AT 6:46 PM

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