I have an issue where the compressor on a '95 Blazer fast-cycles for the first few minutes that the a/c is running/car turns on, then changes over to constantly running. The low pressure cut-out seems to be causing the fast-cycling (on-off at least every second) since the low side pressure drops into the 20's. The high side pressure originally raises to ~150, then gradually raises to very high pressures (250-350) and maintains. When the compressor is constantly running, the low side pressure stays steady just over 30 (presumably just out of the low pressure cut-out's range).

The static pressure is typically 60-70, but each time I turned on the car to test the system, the static pressure would be a little higher each time I turned off the car (the last time it was ~90). I'm thinking that icing might have something to do with this, but I'm not sure.

The history of this blazer: It's my brother's, and I don't believe it's ever had any major a/c work. When I got it the a/c wasn't working, and the static and running pressures were both 0. Because of this I gave it a full charge, 16 ounces, and a few ounces of oil since the compressor was a bit noisy and I also thought that some might have leaked out through a leak. I also added some UV dye, but I have not spotted any leaks. Relays are operating properly, and are not switching on and off with the compressor. Bypassing the low side switch of course prevents the cycling. Central vent air is cool, but warms as the compressor constantly runs (presumably from icing).

What do you think could be causing the rapid fall of low side pressure to trigger the cut-out switch so often, alongside the increasing high side pressure and static pressures? Could this be air contamination? I don't have a vacuum pump, so I just straight added the refrigerant and oil. Could there be an OT blockage? I'm running out of ideas, and could really use your help.

 

Sure sounds like a low charge to me. As the system runs, it warms up and the pressure increases. This is a normal phenomenon. It just sounds like the system pressure is too low when everything is cold.