Confused with my AC system and need help

Ok, now, I'm an electrical and mechanical engineer, so I'm not completely incompetent. I've been dealing with a intermittent problem the last few months. To begin with, sometimes the ac, just wouldn't come on, and if it did, it would only blow air on the slowest fan setting, with thermostat at its coldest setting, and the position of the switch that controls where the flow of air comes from, makes no difference. So, I replaced the resistor for the blower motor. Also, going back real quick, when it wasn't acting janky, it operated like it normally should. Now, the resistor changing, gave the illusion of fixing the problem for a couple days, then went back to intermittent annoyance mode. I began to think that there was a short in one of the plugs behind the head, here's the logic on that. When it was not running correctly, the head unit would become much hotter than normal. Then another symptom arose. When the jeep was turned off, and key removed from ignition, doors opened, then shut, the ac would still be running. Ok, now i have changed the ac blower motor relay, not only that, since i bought the hard top for the jeep, i never put in the new wiring and controller arm for rear windshield wash and new head unit with rear defrost button. Now, i have changed the head unit as well. I know what you're going to say, it's got to be the blower motor. Well, if it were in fact the blower motor, it would have finished burning up by now, and I can tell you that when I ohm out the motor, it reads through the windings correctly, and when the system decides it wants to work, the motor turns just fine, no sound of a shaft bearing, hum, moans or groans. Also, when I go over a mild bump like recessed railroad tracks at a crossing, the ac comes on just fine. So, finally, the question... is anyone familiar with the routes in which the wires are ran, and if so, where is the most likely place for this to occur, or are the commons and their placement or terminations, something I should trace out. Or is there something altogether that I'm missing altogether. Please help

hmmm sounds like you have the climate control AC system. had it in my Grand Cherokee and it behaved like you have described, needless to say it was the worst AC system.

It would blow low and when the AC would finally kick on it would kick off and blow hot to balance the "climate" really a worthless POS.

There is a way to disable it but I've forgotten how.. sorry can't help you more

re-read your post, have you checked for a loose ground? the bump is making something contact correctly and if the head unit is getting hot that would lead me to think it's taking on the role of grounding ...mostly thinking outloud....

What jeeeep said ^^^ it sounds like a bad ground is making intermittent contact. Good luck with your electrical gremlins.

have you checked the fuse in the power distribution box under the hood? I think it's a 40amp fuse, possible partially burnt and making contact when you hit the bumps?

had similar issue with our sequoia that kept blowing fuses in the interior accessories and interior fuse block. drove me nuts until I pulled every fuse and found one of the larger fuses under the hood block was partially burnt and had fuse across another circuit causing overload on that circuit and the other fuses...more thinking out loud

been through that as well

jeeeep said:

have you checked the fuse in the power distribution box under the hood? I think it's a 40amp fuse, possible partially burnt and making contact when you hit the bumps?

had similar issue with our sequoia that kept blowing fuses in the interior accessories and interior fuse block. drove me nuts until I pulled every fuse and found one of the larger fuses under the hood block was partially burnt and had fuse across another circuit causing overload on that circuit and the other fuses...more thinking out loud

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I've gone through that as well, the fuses are good, checked them with a meter as well as the relays. C'mon keep thinking out loud, everybody else as well. 12000 heads are better than one

have you checked the wiring harness under the power distribution block, it's something that a bump is affecting so I'm guessing it's under the hood where things are more susceptible to jolts

The harnesses under the fuse blocks could be corroded. Also, near the starter there's a ground that's just above the starter on the engine block, you can only see it from underneath.

Holy tamale

jeeeep said:

have you checked the wiring harness under the power distribution block, it's something that a bump is affecting so I'm guessing it's under the hood where things are more susceptible to jolts

The harnesses under the fuse blocks could be corroded. Also, near the starter there's a ground that's just above the starter on the engine block, you can only see it from underneath.

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That's awesome. Man, thank you so much, that is an awesome lead. I will check that out tomorrow. If this pans out i might have to bear your children.