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98 tahoe high pressure switch

thepear on Mon August 31, 2009 9:48 PM User is offlineView users profile

Year: 98
Make: chevy
Model: tahoe
Engine Size: 5.7
Refrigerant Type: 134a
Country of Origin: United States

I believe I had a hvac control module failure. The AC switch does not turn on the compressor(and the light does not illuminate on the ac switch). So, I unplugged the module connector that plugs into the module and installed a 12 volt jumper which sent 12 volts to the compressors' high pressure switch. After a little while the 25 amp ac fuse - in the fuse block - blew. I installed a new one and it immediatly blew....According to the wiring diagram of the ac compressor circuit - the 12 volt jumper was connected from the ac/heater 12 volt feed (brown wire) to the high pressure switch (lt. green wire). The other wire that connects to the high pressure switch (dk green/wt stripe) goes to the VCM.
The compressor and the high pressure switch are new. Why do you think the fuse blew twice?
As I look at the wiring diagram, I notice that the low pressure and the cycling switch have grounds connected to them..Does the VCM send a ground to the high pressure switch - thus causing a short to ground?

Chick on Mon August 31, 2009 9:57 PM User is offlineView users profile

Turn the ac on and jump the cycling switch on the accumulator (two wire switch) , not the high pressure switch, you may have burned out the control module, if not, the low side is what you jump, if it gets cold, change the switch, if not, check the pressures, you might have a leak.. hope this helps.. (you have to be careful jumping electronics)
Low pressure (cycling switch) has power going in , then the switch allows power to go out to turn the compressor on, and off when pressure drops below around 24psi....

Email: Chick


Freedoms just another word for nothing left to lose

GM Tech on Tue September 01, 2009 10:02 AM User is offline

How was the high pressure switch installed? by you or did it come with the compressor? or did you transfer it?

You have a dead short in the high pressure switch circuit---either a frade wire- or the switch is shorting internally to ground-- because it is wired wrong, or you have the wrong switch-- or some genius grounded the switch somewhere- thinking it is the type of switch that needs grounding to work.....unplug the HPCO switch and see if fuse blows still- this will tell you the short is before or after the compressor......

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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