Automotive Air Conditioning Information Forum (Archives)

bob234 on Sat August 28, 2010 1:43 AM

Year: 1992
Make: Chevrolet
Model: Silverado
Engine Size: 5.7
Refrigerant Type: R12
Ambient Temp: 95
Pressure Low: 35
Pressure High: 210

I have a odd issue with this truck. It blows ice cold, actually 33 degree vent temps according to my thermometer. Well every here and there the compressor will disengage and stay off for a minute or 2 making the vent temps go all the way to 80. Then it kicks back on and goes back to the 30s. If I turn the A/C off then back on, it will engage and immediately disengage. While the A/C is turned on with the compressor disengaged, I can hear a fast clicking relay noise from the left side of my dash. Once the compressor kicks back on, this noise stops. I thought my compressor clutch was slipping, so I bought a new compressor and converted it back to R12(Why not?), and the new one still does it. I hooked the compressor clutch directly to the battery and drove the truck for a half hour. Compressor stayed on the whole time, but vent temps went all the way down to 28 degrees then I lost air flow due to a iced over evaporator(R12 Rules!!!) So it is something electrical somewhere. Anyone run into this before?

Dougflas on Sat August 28, 2010 3:28 AM

Control head modification may help. Search the tips forum. It is listed there. It involves cutting a green wire and taping it off.

GM Tech on Sat August 28, 2010 7:55 AM

The a/c relay is under the dash at precisely the point you hear the clicking sound-- swap it out or replace it (much cheaper than the compressr) the rlay is probably worn out---access it through the glove box opening after you drop the glove box... sure would have been nice if you would have described the problem before you bought the compressor.......

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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......