1993 W250 AC Compressor Won't Cycle
 

Hi, new to the world of Dodge trucks, recently picked up a 1993 W250 with the 5.9 magnum V8 in it. I was told the AC in it didn't work, but when I pushed the button to set it to AC it did actually work and was quite cold. However, ever since that drive I have not been able to get the AC to work, because the compressor clutch won't engage. So I investigated and unplugged the AC cutout relay under the hood, where I was able to get the compressor to cycle if I used a jumper wire between the two AC wires. I used a multimeter to check if the relay was receiving voltage across the other two wires, and it was. Easy fix I thought, just replace the relay with a new one and you'll be on your way. However, upon replacing the relay with a new one, it still refuses to work as it should. I am now out of ideas and have had zero success finding any wiring information for the climate control system. Any suggestions on where I should look next? Could it be a poor ground on the solenoid signal wire, and if so where is it grounded?

The ac is actually controlled by the pcm, You will have power at the relay but the pcm supplies the ground for it to energize. After that there are two cut out pressure switches that will cut the power to the compressor if the pressures are to high or low. Check if you are getting a ground for the relay first.

Make sure the system has a charge. If the gas is too low the compressor will not engage..

Is the system full? It's nearly 30 years old so some refrigerant may have seeped out. The low pressure safety switch on the receiver/dryer will cut the compressor off to protect the system. You can jumper the switch with a piece of thin wore. Is on the dryer somewhere. The dryer is a coffee can looking thing on the left of the firewall as you stand in front of the truck.

Keep in mind 1993 was the last year for R-12 refrigerant. It's in the unobtainium section of the parts store. If the truck is otherwise in pretty good shape, and hasn't been already, it would be a candidate for R-134 conversion.

Ok, I had not considered that. How should I check the relay is getting a ground?
I guess I hadn't thought of the refrigerant being low, since when it worked it was quite cold. This said to me that it wasn't low, but I'll try jumping the switch in a bit.

The low pressure switch is actually located on the expansion valve in this '93. Jumping the connector with a wire made no difference, still wouldn't engage the compressor.

There is also an electrical thing in a black box mounted right next to the expansion valve. It has 5 wires total, looks like 2 go to a probe in the refrigerant line and the other 3 run into the wiring harness. Does anyone know which wires should be jumped to bypass this? I imagine it's measuring refrigerant temperature to keep stuff from icing up.

Issue was a connector had come undone on the heat/AC control unit.