I had my AC system serviced in my '98 2500 360 magnum, and the technician told me the system vacuumed like it should, but there's not power to the clutch, I'm thinking relay issue, but if any of y'all have an idea of what else it could be, please let me know before i tear in to the system completely.

 

Power to the compressor comes from the relay in the PDC. (black box behind battery.) Relay is controlled by PCM. PCM gets its clue from the hi/lo pressure switches, and the control head. If the control head says it wants a/c, and the PCM sees voltage on the hi/lo pressure switch circuit, it will activate the relay. So, lots a possible problems there. You can try just swapping out the relay, and see what happens. If that doesn't work, try bypassing the pressure switches, one at a time, and see if that doesn't wake it up.

 

Im having the same problem with y a/c on a 94 dodge 1500. but i have no power going thru the wires the pressure swithes are on. And also on the climate control unit inside the came it has a plug with 7 wires but the green and yellow one is neither a hot nor ground and not sure where it goes.

 

there's no power after the relay, i tested the fuse and it has power, switched out the relay, still no power at the plug for the compressor.
maybe there's a ground not connected? I'm unsure, and this summer is going to be hot, and would like AC.. i went all last year without, of course, i cant complain too much, i only paid $500.00 for the truck..

 

Do all the plugs for the relay have power? There should be two that are hot, one constant and one thats on with the ignition and two grounds i beleive.

 

PCM controls the Relay. Put a jumper in the low pressure switch, see if the compressor runs. If it doesn't, also put a jumper in the high pressure switch, see if the compressor runs.

 

So if you jump the low pressure switch and the compressor runs, what is the problem? A/C need a recharge?

 

Yep, either you are low on refrigerant, or, the switch is bad.