HVAC Control Unit Wiring

[LucaScali]

Hi,

Could someone please point out which wire in the truck is controlled by the red slider? It's meeting resistance/pull back before the down arrow and doesn't seem to route much if any hot air downwards. I've looked in the truck and nothing seems to be binding, but wasn't quite sure which wire in particular should be traced.

Any suggestion to resolve would be appreciated.

[EC900]

Is this a new problem that just occurred or a new to you problem due to new ownership?
Anyway, it’s a two-man job.
What I do when working alone is set up my camera to film what’s going on when I manipulate the controls. Reviewing each time to see what’s moving. That way I’ll know which cable is doing what and when. This also can be done with “witness lines” by marking or placing tape on a cable to measure its movement, one at a time.
Whatever is going on - Don’t Force the Slider !
It can also be binding up under the dash, and wiring is causing the obstruction. The grease on the mechanism might to gumming up or worse, rusted. So try a little penetrating oil and see if that will help if there’s no obstruction seen under the dash.
Unfortunately my trunk compartment cover is in place so I can’t advise which cable in there does what, but I was able to manipulate my Red heat slider and for what it’s worth it’s stiff (due to cold weather) but operating the flap.

[LucaScali]

Thanks, EC. It's a new problem that just occurred. It's more tugging than binding, as if something is interfering with the cable somewhere. There's no rust or anything blocking the slider itself. Was working in the truck recently to get at the steering joints and a brake light switch, but I'm unable to find where I disturbed anything. Last night I removed a couple hoses to see if there was anything was obstructing or pulling on the cables, but it all looks ok.

I guess if we can't determine which cable does what, I'm going to have to recruit someone to observe.

[Jonny H]

As you are looking at the frunk, the red lever cable comes in on the back of the right hand blend valve. It attaches to a lever which pivots on the valve Another cable goes across the car from this to the left hand side. Both move at the same time so that the red knob opens both blend valves.

[LucaScali]

Appreciate it, Jonny. Not quite sure what you're referring to, but I'll have a look on that side and maybe take a pic to confirm. If anyone is able to post a pic in the meantime, it would probably help.

[EC900]

See if this post is of any help determining the cable functions -

http://forums.pelicanparts.com/porsche-911-technical-forum/427501-heater-vent-control-cables-76-a.html

[LucaScali]

Thanks EC. That thread helped illustrate Jonny's instructions. Nothing seems to be interfering with those cables and they don't appear kinked anywhere. I don't necessarily need hot air in the footwells, but knowing it won't slide all the way left is triggering. It's like something is tugging on the cable, but even when I force it all the way left, it doesn't seem to operate the flap.

Maybe I disturbed something when I installed a new head unit in 2021 and didn't notice until now. I guess I'm going to have to get under there, because the cables in the truck are a dead end so far.

[LucaScali]

Guys, sorry if this should be obvious, but where do I access the valve being actuated by the lever? Maybe it's snagged.

[EC900]

It’s a flapper that’s in the air distribution box in the trunk, likely the center master, at least that’s where I hear it open/close when I move the Red slider.

I think your new radio or bracket might be the problem???
The wires real could be a problem, maybe the antenna wire but as you see from my pics that’s a crowded space. I looked under my 77 and it’s very close to the rear of radio head, about 1/2” space. Not much else to interfere with that yellow metal hinged bracket. Tough to get a good photo, I can only see so much under the dash, and operated the Red slider to see its function. Check out the location of the bracket that the cable attaches to for a reference maybe you can look at yours…
Pic 1 is with the Red slider to the Right Pic 2 is to the Left
(I may have reversed the order - being upside down !)

[LucaScali]

Thank you very much, EC. I really appreciate your advice and help in getting me these pics. Exactly what I was looking for. I think you might be right. I'm going to have another go at it tonight.

[LucaScali]

The bracket holding the plastic cable sheath in place was loose allowing it to move with actuation of the lever, which caused the cable to bow at the end. Tightened the little 8mm bolt and straightened the wire. All is good!