Long time jeeper but new to forums. I have an a/c issue that has me stumped and I am hoping for some advice as reading the forums has helped me solve a litany of other problems. Jeep is a 98 TJ with a 4.6 stroker that I am just wrapping up a frame off restoration. AC is new, system is charged to specs. Low pressure and high pressure switches are working as published. Now for the fun part. While troubleshooting the system I first attempted to jumper the wires that plug into the low pressure switch to determine if I had a bad switch. Jumping them did not work. Next I grabbed a test light, grounded it on the battery and stuck it in the wires to see if voltage existed in the wires. Suddenly the compressor sprung to life and the system worked great. So, when I inadvertently ground the wires that connect to the low pressure switch the system works. However when I disconnect the ground and plug the wires back onto the low pressure switch the system doesn’t work. I have ran continuity tests on all of the wires in the system and can’t find any breaks or shorts. Do I have a bad system ground? Any thoughts? I will leave my oil pan/ rear main fiasco for another thread! Your help is greatly appreciated!
I don't really understand what would cause it to do that either. Looking at the schematic, both of those switches are in series within the A/C switch sensing wire that goes into the PCM.... if that circuit is open from either switch, the compressor clutch should not engage. The signal wire running to the compressor clutch relay comes directly from the PCM. So basically, your PCM senses 2 things before it sends a signal to the clutch relay: the hvac switch is is turned to the proper setting on the dash, and that both A/C system switches are closed. Once it confirms that, it then sends the 12v signal to the clutch relay. There is no ground wire coming off of the compressor so maybe you have a bad compressor case ground? I'm not sure....
First off, thanks for taking the time out of your day to lend some advice! Your disscussion made me question a couple of my previous conclusions. First, should I be able to register voltage on the wires that plug into the switches? I can't right now so I assumed that the switches just completed a ground when activated. Was my assumption wrong? Secondly how do the switches work. Right now the system is charged to specs and at the low pressure port with the compressor running I read about 47 psi. That said, when I test continuity on the switch itself I get continuity which led me to believe it is working. (I have also replaced it once just to make sure!) However when I test continuity on the high pressure switch I don't get continuity. I deduced that it was working as well and that if I reached my high pressure threshold that the switch would activate and I would be able to read continuity. Am I incorrect? Does the high pressure switch work in the opposite direction and should have continuity when the pressure is within correct specs? I'm going to go run a ground jumper to my compressor to check your other theory. Thanks again!
I use mine all of the time and it is an indispensable tool for working on my Jeep! If you have trouble downloading the manual let me know and I'll figure something out. Also, if you have more questions let me know; I'm an engineer so I enjoy working on problems like this!
Guys, thanks for the inputs and the schematics. I grounded everything in sight with no luck. I already had a great chasis, firewall, and block ground with new battery cables as well but I ran a few extra jumpers just in-case I missed something. No love! I will pour over the schematics Wes was nice enough to post and see if I can track the gremlin down. I will let you know what I find ......if I ever do! Thanks again.
Update: after tracing every wire I finally figured out that both my high pressure and low pressure switch connectors were not making contact on the switches. Tough to figure out because when I jumped them the larger diameter wires would make contact just fine but when I plugged them in they wouldn't work. Couple that with the fact that both connectors were bad and it really had me scratching my head. It didn't have air for 13 years so the connectors were just exposed to the elements. Cleaned them up, resized them, coated with dielectric grease and the new ac from jeepair fired right up as published. On to my rear main seal issue!