I have a 1996 Blazer 4.3L 4WD 4dr and am looking at charging the AC with R134a. Last fall as the AC was needed less I noticed a small amount of oily residue around the hose fitting that connects the high and low pressure lines to the compressor. I unplugged the compressor so that it wouldn't run with low R134a.

Today I quickly replaced the seals so as to keep contamination to a minimum and replugged the compressor connector. I hooked up the R134a filler hose (it has a gauge) to the low side and pierced the can of R134a and started the vehicle, then turned on the system to max. The compressor clutch didn't kick in so I couldn't fill it. I tried shorting the low pressure sensor plug that is on the accumulator; but that didn't work either. Is one of the 3 relays at the top of the firewall an A/C relay, if so which one? Could my compressor's clutch be bad? Is there another way to kick the compressor on; such as putting a low amp 12v jumper directly on the compressor itself (it has 2 leads on it's plug)? Any help would be appreciated.

 

The VCM ultimately controls the clutch but there are several things that can inhibit clutch operation.

The clutch relay is located on the firewall, there are 4 wires attached to it:

Pink: This wire feeds the latching coil in the relay. It comes from instrument panel, (I/P) fuse #4 labeled GAUGES. It should show battery voltage in the RUN and START position of the ignition switch.

Orange: This wire feeds the clutch coil when the relay is latched. It comes from the I/P fuse #14 labeled AC COMP. It should show battery voltage at all times.

Dark Green: It goes directly to the compressor clutch coil positive terminal.

Dark Green with white trace: This is the trigger wire for the clutch relay. The VCM supplies ground to this wire which latches the relay and connects the orange wire to the dark green wire, (inside the relay) to energize the clutch coil.

There is a normally closed high pressure cut out switch on the rear of the compressor that supplies battery voltage to the VCM. If pressure is excessive, the switch opens and no voltage is sent to the VCM. Without voltage on this wire, the VCM will not allow the clutch coil to be energized.

The clutch cycling switch, (on the accumulator) has a dark blue wire that receives battery voltage from the VCM. The cycling switch is closed, (to ground) above ~42psi, (allowing the clutch to engage) and opens when low side pressure drops to ~22psi, (causing the clutch to disengage).

Check this stuff out and post your results.

 

Also how long were you trying to fill it? If it was completly empty sometimes it takes awhile, then the compressor will short cycle, then kick in and stay on.