jessenator

So I went over to my mechanic neighbor's house to recharge Bertram's A/C and finally drive without fear of cooking inside my Jeep. Turns out I got other problems.

The compressor doesn't kick on, even with enough pressure (it had previously but only for short bursts), but this might be more related to the main point: the main output B+ shaft nut on my alternator started glowing red. I shut it off, waited, and restarted without running the fans or any other aux thing other than the engine, got home, and it was glowing again.

I'm guessing there's a short or bad ground somewhere under my hood...

I haven't had any weird mechanical maladies or symptoms that I'm aware of, having been driving it for several months now daily. Normal volt indicator (which I'm sure is more an idiot gauge than actual voltage), no crazy anything. My fog lights don't work, and that's about the only thing electrical (aside from the compressor) that doesn't work.

I know the front block ground is tight and working, as is the battery terminal-to-body ground... I daren't dig up rear body ground hidden beneath the trim unless I absolutely need to.

Specs: 1998 Cherokee XJ | 4.0 | 154k miles | 4dr | 4wd | classic trim | all oem aux stuff/original

The alternator is the original, as I snapped a field terminal off my spare that should've been in it. It went through an engine overheat and spewage of brown rust water, but spun okay when I had it on the bench.

I'm very, very novice when it comes to wiring (in fact I fear almost all forms of car wiring), only having handled the simple circuits of guitar pedals. Where's the first place to start detecting this short (if I'm correct assuming it's a short)? or maybe it's a bad alternator?

thanks in advance

fb97xj1

Too much resistance and things get hot. Could be a loose connection, or dirty. Or both. Remove it and clean the connections, and check the voltage with the engine running. Ive seen this happen on a few Fords, and it was a loose connection or bad cable. Id imagine the same can happen with an XJ.

jessenator

Thank you.

Dumb question, but check voltage on what, the alternator output post?

Edit: I did a Google search (should've been step one—did it here but found it, yup, on a Ford forum!) And I bet it's a bad voltage regulator. I'll check the Volta this morning. Lucky I have a short commute.

jessenator

Welp... Time to get that spare alternator fixed

Wentto tighten it (it was definitely loose) and now it's hosed. Guess I'm not driving the jeep today! Lol.

So there's that lose connection, possible bad voltage regulator, and I found a ground disconnected... *Facepalm*

s346k

jessenator

Lol What can I say?

97grand4.0

high resistance in that output terminal - bad connection, rust...time for a new alt.

jordan96xj

Its surprising you didn't bump into more issues. You probably had just enough amperage coming through to handle the ignition load. But limited amperage/voltage from a connection like that can definitely cause the electromagnet on the compressor clutch to not engage. So hopefully that problem will resolve once you correct the alternator. I had a very similar issue on a Subaru, where I chased a compressor clutch problem for a long time thinking it had to be an AC problem of some sort, only to eventually realize it was a weak ground from the alternator that was causing the problem. Nothing else on the car had symptoms, other than that the battery never seemed to be as strong as it should be (sluggish cranking during start, but never failed). Long drives would get the battery charged, but lots of small trips would allow it to deplete.

fb97xj1

Thatll do it. Looks like that stud welded itself to the nut a bit. No saving that one.