Hello all,
New to this.
I have a '98 RAM, 5.9L, 4 wheel drive, quad cab. Actually, it's my son's truck. 2 weeks ago his a/c stopped working. I checked power to the clutch and there is none. I have checked the fuse and relay and they are good (also replaced both, just in case). I have check wiring from clutch to fuse panel for continuity and all wiring I can find relating in the engine compartment seems to have good connections and grounds. When I apply direct power to the a/c clutch, it kicks on and blows cold. As far as I can tell, the freon pressure on both the low and high sides are within tolerance while in operation. I have checked wiring from PCM back to the control in the cab. Though I get continuity for pins 22 and 23 back to the same wire on the control (LG/WT). Pin 1 from the PCM tests good to the relay. This may not be the best idea, but my son picked up 2 used PCM's from the salvage yard just for grins and neither of them fixed the problem. I don't know what else to look at nor do I know how or what to look for at the high and low switches. Since my operational pressures are withing parameters, I don't thinks its the switches.
Can anyone provide me other ideas of what to look for? Also looking for a wiring diagram of the control inside the cab. I have not been able to trace those wires or test the control to see if it is bad.
Thank you for your help.

 

Check low and high pressure switches. That circuit needs to be complete for the PCM to engage the relay, that powers the compressor clutch.

Did you put gauges on it? What was low side pressure looking like?

 

I agree on the pressure switch advice. If your system is full of R134A I would try unplugging your low pressure switch on your canister over on the passenger side it’s a sensor that goes into the ac system try jumping the harness with a wire for a second and see if the compressor kicks on. Don’t do it very long just long enough to see if it kicks on. If it does just buy a new sensor you don’t drain the system to replace it it’s really simple to replace just unscrew it and screw the new one in.

 

We took it to a "mechanic". All he said was "could be the low pressure switch. Can't get them anymore" . I knew right away he did not know anything. I removed the switch and put gentle pressure on it and nothing (used volt meter to determine continuity). Found one at junkyard. did the same thing and this one had continuity. still did not get clutch to come on. We checked the high pressure switch and have power there. I told him to leave it alone. he then purchased an ECM. That did not help.
The "mechanic" told us refrigerant was good.

Thank you.

 

dodgedakota98luver

I am new at this.
We did check continuity but did not jump it. I will try that. Never though of jumping it when I replaced the sensor.

 

At 22 years old, I'll bet your refrigerant pressure is just low. The pressure switch cuts the compressor out to protect the system if that happens. Use a piece of wire, mechanics wire will work, and jumper the switch. If the compressor engages when you turn the a/c on, just add some refrigerant. There are lots of kits out there with a gauge and you just hook it to the low pressure side. Hook the switch back up and when you charge it, I'll bet it starts working. This is the wire connection on your receiver/dryer on the passenger side of the firewall.