Climate control / HVAC dead, stuck on full defrost

[Black88GTA]

Hi all, sick of me yet?

Yet another issue with my poor '92 that I can't seem to find an answer on.

The climate control / HVAC was working fine when I powered it up late last summer (after sitting for over 11 years) - everything lit up properly, buttons worked, the system responded properly to button presses, etc. A/C blew warm, but the blower motor functions / vent selector worked, at least. It worked fine up until yesterday.

Yesterday, when I went to move the car so I could do brakes on my van, the climate control all of a sudden went nuts and started blowing air full speed from the windshield vents. The first time this happened, there were a few lights on on some of the buttons (no response to buttons), but the temp display was dark. Now, the climate control unit is completely dead, with no lights on anywhere, and the system seems to be stuck on full-speed defrost.

Video: https://youtu.be/nXv3yfe1Sew

Anyone know where to start troubleshooting this? Or am i going to be pulling the HVAC unit from my parts car?

I know there is a known issue with the more sophisticated unit used across the pond, but can't seem to turn up much as far as known issues with the US HVAC controller.

Thanks in advance for any help!

[irox]

Hi,

I had a s seemingly dead HVAC, but it turned out to be a faulty T(Timer)CU causing a voltage drop. Unplugging the TCU made the HVAC work again. I didn't have the blower stuck on, or any lights on the control panel. If you pull the unit, it's probably worth checking power and ground before installing the donar unit.

Good luck!
Ian.

[Black88GTA]

Originally Posted by irox

Hi,

I had a s seemingly dead HVAC, but it turned out to be a faulty T(Timer)CU causing a voltage drop. Unplugging the TCU made the HVAC work again. I didn't have the blower stuck on, or any lights on the control panel. If you pull the unit, it's probably worth checking power and ground before installing the donar unit.

Good luck!
Ian.

Thanks, good tip. On the list of things to check when I can get into it again.
Looks like this shouldn't be too hard to get at / swap out if needed...much easier than swapping out the HVAC unit at any rate. I suspect someone's been in there before also, as the glove box already mysteriously has screws removed from it

Any idea where the main grounding point is for the HVAC unit? I'd like to check that out as well while I'm poking at stuff.

[irox]

I dug out my "notes" from when I was fixing my HVAC problem:
https://www.subaru-svx.net/forum/showthread.php?t=64528

A few things share the same ground/power line. Checking the cigarette light voltage and ground resistance may be a quick to see if something is dragging the voltage down.

Cheers,
Ian.

[Black88GTA]

Originally Posted by irox

I dug out my "notes" from when I was fixing my HVAC problem:
https://www.subaru-svx.net/forum/showthread.php?t=64528

A few things share the same ground/power line. Checking the cigarette light voltage and ground resistance may be a quick to see if something is dragging the voltage down.

Cheers,
Ian.

Thanks, this is helpful. I can't find my DVOM at the moment, so can't check voltages until I locate it but I was able to go in and unplug the Timer Control Unit in the hope that was the problem. The behavior is unchanged, so it seems that's not it at least.

Once I locate my multimeter, I will start to check other things but I have a feeling I'm probably going to be swapping out my climate control unit :/

[Black88GTA]

So I got into the parts car over the weekend to pull the sunroof assembly so I can fix my sunroof problem once and for all, and decided to pull the HVAC controller while I was in there to see if maybe that was the issue. Turns out that it was, and it seems to be all resolved now. Good for me, because now I don't have to go hunting for wiring faults... with the HVAC at least. I still have a passenger window that won't go down, and swapping the driver's switch array didn't fix it. Yay more stuff to figure out! Getting there though...slowly...

[irox]

Awesome!

Tracking down wiring faults sucks, glad your free of that for the HVAC.

[Black88GTA]

Originally Posted by irox

Awesome!

Tracking down wiring faults sucks, glad your free of that for the HVAC.

Thanks although I'm now wondering what exactly caused it to kill itself. Old age? I didn't inspect the electronics too closely, although I did open it up in order to swap faceplates (since the woodgrain of the 94 parts car didn't match that of the 92 runner). I gave the boards a quick look, but nothing jumped out.

I don't think I have any voltage problems, but ordered a cheap cig lighter voltmeter w/ USB ports from Amazon to keep an eye on things just in case.