Last summer I had to top off my A/C system with R-134a. I must have a slow leak somewhere. Over the winter it has seemed to almost all leak out. I topped it off again, but my compressor clutch still wont engage. If I put 12v directly to it, it will engage. On the dryer there is a socket where it looks like there should be a harness plugged in. This is the low pressure switch, correct? There are no wires/harness plugged into it. I looked all around for the harness dangling somewhere. I can't find it anywhere. I don't know how it ever got unplugged. Can anyone tell me where I might look for it, or maybe have a picture? I searched the internet and can't find a good one. It has to be somewhere close. I checked all fuses and everything, and like I said everything work great and is ice cold when I put 12v to it and engage it "manually". It's a 99 ZR2 4.3L if any of that matters

Thanks

 

that is the high side pressure switch, the low is on the back of the compressor. and yes if that's unplugged (or either switch is unplugged for that matter) the clutch will not engage

 

I figured that was the low switch because it's on the same component (dryer) as the low pressure port to add R134a. Anyway, I found the harness that plugs in this morning. I was looking for it coming from the middle of the engine bay where a lot of the other wires come from. It come from the other side closer to the fender. Everything is good now 100%. Besides the leak I guess.

Thanks

 

my 04 blazer has 2 plugs over there for some reason... not sure if the previous owner spliced one in and never removed the old one? AC didn't work either way when I got it, I'm working on that now lol

 

The switch on the accumulator is the clutch cycling switch. The switch engages the clutch when low side pressure is above ~42psi, and disengages the clutch when low side pressure drops to ~22psi. The switch on the rear of the compressor is the high pressure cut out switch. If high side pressure is excessive, (~375psi or more) the ground circuit for the clutch is opened and the clutch disengages. If either switch is unplugged, the clutch will not engage.

 

ah okay you are right, I had it backwards... I did find out on mine yesterday though that the previous owner did in fact splice in a second connector trying to get the AC to work. The original plug was fine, it was the switch on the accumulator that was bad :P replaced it and all is well