A/C compressor not working properly

Tiny
SGPON
  • MEMBER
  • 1998 CHEVROLET 2500
  • 7.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 260,000 MILES
I just bought this truck (listed above) and the A/C is not working. Fuses and relay tested to be fine. When I jump pins 30 and 87 the compressor engages. There was 0 pressure on the low port, so I added 2 cans and got it to 20 PSI (still low, I know, but I only had 2 cans nearby). It's still not working without jumping. High and low pressure switches both light a test light but voltage on each will hit 11.3 and then drop to nothing (but still enough to light the LED test light) (using a snap on test light with built in voltmeter).

Maybe it still needs more refrigerant to trigger the switches? Or is there a bigger problem with those switches not seeing voltage?
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Monday, May 3rd, 2021 AT 8:59 AM

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Tiny
STEVE W.
  • EXPERT
Posted this on the earlier thread so I'll copy it here in case you miss that one. The testing and other procedures were all in that thread so I won't duplicate that here.

20 PSI would still be a low charge. That system should hold between 32 and 38 ounces depending on the cab. You put in 24oz if the cans were full. You should be able to use a set of gauges and add in the rest and then see if the system cycles. However with the system pressure at 0 you should start by pulling a full vacuum on the system and see if you can find the leak, or with the last can use one that has dye in it. That way you could find the leak instead of just needing to keep adding R134a.
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Monday, May 3rd, 2021 AT 9:18 AM

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