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High Pressure

claytl on Thu October 18, 2007 3:51 AM User is offline

Year: 1992
Make: chevy
Model: 1500 pu
Engine Size: v6
Refrigerant Type: r134A
Country of Origin: United States

I switched over to 134A about a year ago and system has been working fine. I have checked the freon level several times and the gauge has always said 45 (Charged) and worked fine. Now the compressor is not engaging and the gauge reads 100 and when I pull off the cap to test it it is leaking. What could cause the pressure to jump?

claytl on Thu October 18, 2007 4:39 AM User is offline

I had a problem with the pressure switch making contact with the wires. I had to move the plug about every other day to make it make contact, It had two little pins and did not make good contact. I went to a junk yard and bought a new switch with contact blades and the connector and wired it into my system. Worked great for about month and a half. Now it has a problem high pressure at switch keeping compressor from engaging.

badufay on Thu October 18, 2007 9:33 AM User is offline

i am assuming that is the pressure from the low side. Since the compressor is not engaging the a/c is not compressing anything. That 100psi reading is normal for a static pressure ( a little high i think, but i am sure someone could argue otherwise). That 100 will stay 100 until you find out why the compressor is not engaging. Check all the electrical connections on all the switches for the system (coolant temp sensor, pressure switch(s), etc...) You need a wiring diagram to find out what exactly you have, and then you can find your problem. Get a multimeter and disconnect the electrical switch from the compressor, turn everything one that is supposed to be on and see if you are getting the needed 12 volts.


mk378 on Thu October 18, 2007 10:20 AM User is offline

Like the other guy said, it is normal to measure 100 when the compressor is not running, and the switch should be closed with a pressure of 100 (it only opens when the pressure is less than about 25, and closed at other times). Unplug the switch and jump between the wires in the plug, if the compressor now engages the switch is bad. If not maybe you have a bad connection where you spliced the "new" plug in.

If you need a new switch you can just unscrew it and replace it without removing the refrigerant, there is a valve under the switch that will close when you start to unscrew it. Also finding some pressure under the plastic service valve cap is normal, just make sure the cap is on securely when you're done.

In order to do any serious repair or recharge work you really need a gauge manifold set with two gauges.

bohica2xo on Thu October 18, 2007 3:04 PM User is offline

Death Kit installed - Check.

No high pressure readings - Check.

System no longer working - Check.

A bad switch or connection may have just saved you some money. In addition to the cycling switch, there is also a clutch relay in the compressor circuit.

First order of business is a flush to remove the mixture of oils, and possibly refrigerants. Then evacuate & recharge to factory specifications.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

claytl on Fri October 19, 2007 2:26 AM User is offline

The leaking was a valve that had backed out. Tightened it and fixed that problem. I got a new pressure switch and it looks like it is fixed, thanks.

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