3 & 4 are the grounds

 

You said you checked all the fuses. What about the relay ? Specifically #30, in cabin box, which should be for the main HVAC controls.

Chasing down wiring issues can be frustrating. That used to be one of my tasks back in my automotive tech days.
(Maybe that's where my gray hairs came from. )

 

@donbrew - Thanks for the diagram -- very helpful! I located the two grounds and they both looked clean as can be. Not even anything to clean up, but just in case I scuffed them both with steel wool (ground posts and terminal ends both) and even tried swapping their positions. No change.

@firemangeorge - Yup, checked the relay as well and in fact I discovered that the panel, when it chooses to light up, does so with or without the relay.


After reading these suggestions, I went back out and pulled all the fuses once again. Coincidence or not, after doing this the panel lit up again ... for a few key cycles. Then it was off again. If I let it sit with the key on for awhile, a couple times it eventually lit up, but then it didn't after doing several more power on/off cycles. Gave up and reassembled enough to be able to drive it (left the waterfall off and other trim panels) and when I went to run an errand half an hour later, it was magically working again ... for a couple key cycles, and last I checked it was dead again. Very frustrating. Looking like I'll end up at the dealer, but I hate the idea of paying them shop rates to chase electrical gremlins. Could get expensive in a hurry.

 

Sound very much like a bad relay somewhere. I will try to look some more.

 

Thanks, donbrew. Really appreciate the guidance and support!

 

Following up on this, I still haven't figured out the problem. The dealer wants $78 just to hook it up to the machine, and that doesn't include or even go toward actually fixing the problem. It continues to come and go without rhyme or reason. It will work for several days, then quit for several. I've been driving around for about a month now with the center dash torn apart and rags stuffed into the center vents to keep full-on hot air from blasting into the car those times when it decides to quit working.

As mentioned previously, the grounds look immaculate. Donbrew (or anyone else), do you have anything that would indicate if a common relay is involved in the circuit(s) that power everything in that HVAC control cluster apart from the fan itself? Again, when the problem kicks in it affects hot/cold selection, power seats, inside/outside air, AC toggle, rear defrost toggle, and the vent selection (floor, dash vents, defrost vents, etc.).

I'll take it somewhere if I absolutely have to (can't have full-blast hot air going if/when summer ever arrives) but right now I'm still hoping it's something I can resolve with enough guys smarter than me giving me free advice on the Internet (that I can pay forward some other way).

Thanks again,
Brent

 

There is a ground that would explain the power seats and your outside mirrors. It is ground 301. It is under the drivers seat just under the carpet.

But ground 301 won't explain the hvac problems. I'm would be looking at the under hood fuse box. Poor connections inside the box could be the cause for all of you problems.

Try giving it a shake, tug,pull, tap and see if the hvac flickers or go's out.

I have also seen the connectors that plug into the fuse box from the bottom get pushed out of place or bent.

 

Good call Lucky, that could be the issue

 

Power seat works fine, just not the heated seats -- and that's only occasionally when this problem wants to rear up. The power mirrors, on the other hand, have never worked since I bought the car. (It was a salvage title, hit in the front but no airbags deployed -- just sheetmetal replacement.) Discovered a few weeks ago that I can make the DS mirror go up, but that's it.

Regardless, I'll look for that ground and check the other things you mentioned. Even if it doesn't fix the bigger issue, maybe it'll help with the mirrors. Appreciate the ongoing help!

 

Just wanted to follow up on this thread and say that after living with the issue for 7 months since first reporting it here, the problem is solved. I stubbornly refused to pay the dealer for a diagnostic fee and couldn't find any wiring issues myself, so I just kept driving it as-is, even with the heat going full-blast throughout the summer. It was miserable. Long story short, it was the control panel itself that had gone bad. Driving in the summer without AC was one thing, but since it's gotten cold it's really quite important that things like the defroster work, so I decided to roll the dice on a replacement panel. Spending $75+ at the dealer just for a diagnosis was a guaranteed loss of $75 that wouldn't go toward parts or repair, so I dropped $40 on a new-to-me panel from eBay, even though I don't like blindly throwing money at parts. Received and installed it last night. Problem solved. Wish I'd done it 7 months ago, but with several separate switches in the thing and the fan controls still working, I didn't think it could be that somehow the whole thing (except the fan speed control?!) went bad. Live and learn. *sigh*

Thanks again to all who offered suggestions!

Brent

P.S. Solved the power mirror problem I mentioned in my previous post by replacing the controls with a brand-new switch. I had gone through a couple used ones from eBay that were supposedly tested good from sellers with excellent reputations. Those must have been bad, too, because the Dorman replacement, although kinda crappy in terms of the feel, works perfectly. For the moment, for the first time since I bought the car, everything is actually working. ***KNOCK ON WOOD***