Vehicle: 2003 WJ, 4.0L Engine, Manual A/C System
Ever since I got my Jeep it has had an A/C system issue. First it kept blowing the 15A fuse in the engine bay. I found a short where the wires pass through the metal wire loom next to the head. So I replaced that section of wire and added rubber grommets where the wires go into and out of that metal loom. Then it worked fine for the entire last half of summer.
It has also had the issue where the actuator would change from cold (or heat) to it's middle position. I would have to tap on the temp control knob to get it to go back to where it was suppose to be. So I took the control panel apart, got a new potentiometer, and soldered it in place. That problem was solved.
Now I just noticed the latest problem today as I decided to test the A/C system before it got hot. I turned it on and low and behold, the same 15A fuse was blown. So now I broke out the DMM in the little amount of time I had before it got dark. What I found was rather peculiar.
With the engine on and A/C button pressed on, the resistance from the fused side of the fuse to ground was 0 ohms (short circuit). When I turned the A/C button off, the resistance jumped to 18 ohms.
So my first thought was the relay is bad. So I pulled the relay and measured the resistance from pin 87 to ground. With the engine off, the resistance was 18 ohms. With the engine on, the resistance was 0 ohms (short circuit). Neither of those two measurements mattered if the A/C button was on or off. So with that I concluded the relay is not bad, it's something else down the electrical line.
Does anyone know what would cause a short circuit while the engine is on, but measure fine while the engine is off?
Tomorrow I'm going to disconnect the plug at the A/C compressor and see how it measures. But I'm guessing once that's disconnected, it's going to read open circuit when the engine is on and off. If that's true, that means it's part of the A/C compressor or compressor clutch. Are those parts always the same? Or can one part be replaced without the other?
Ideally I would like to fix this issue without having to take it to the shop to evacuate and recharge my A/C line. Does anyone have any ideas what would cause possibly cause the system to measure 18 ohms with the engine off and 0 ohms with the engine on?