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1990 K1500 only cools with high pressure switch jump

duruser on Sat July 10, 2010 2:30 PM User is offline

Year: 1990
Make: Chevrolet
Model: k1500
Engine Size: 5.7L
Refrigerant Type: R134a
Ambient Temp: 85
Pressure Low: 105
Pressure High: 110

I am converting my truck from R12 to R134a. I have replaced the accumulator, replaced all the seals except the two on the compressor, replaced the expansion tube, flushed the condenser and blown air through the evaporator. I put eight ounces of TEXACO CAPELLA HFC-100 refrigeration oil in the accumulator. I evacuated the system at 30HG for an hour. I waited an hour and evacuated the system for an additional hour.

I charged the system with r134a (I use the 12 ounce cans sitting warm water) with only the low side valve open and started the truck. Before the first can was empty, the compressor clutch begin to cycle on and off and eventually stayed off. I have jumped the high pressure switch (10 seconds at a time) to get about three cans of r134a in the system, but the clutch will not stay engaged.

When I jump the high pressure switch, the accumulator immediately gets cold as well as the input and output lines. The compressor sounds as though it is running well without any noise or strain.

Your help would be appreciated. Thanks,in advance, William

Chick on Sat July 10, 2010 3:04 PM User is offlineView users profile

Disconnect your battery for a few minutes to reset any codes.. Should only jump the cycling switch..if that doesn't help post back....

Email: Chick


Freedoms just another word for nothing left to lose

duruser on Sat July 10, 2010 4:21 PM User is offline

Thank you for responding, Chick. I disconnected the negative terminal from the battery for ten minutes and then re-tried. The pressures and results remained the same.


duruser on Sat July 10, 2010 8:02 PM User is offline

I have been able to determine that the source of my problem was the pressure sensing/cycling pressure switch that is located on the accumulator. According to the parts catalog, there is a switch for R12 and a different switch for R134A. Fortunately, I did not have to discharge the a/c system to replace the switch. The switch fitting is equipped with a schrader-type valve, so I just screwed off the old and screwed on the new. When I turned on the a/c, the clutch begin to cycle and I was able to finish charging the system.

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