Constant heat / flapper box help

[mziin]

Hi folks,

I know, another thread about this!
I spent some time reading and searching on this forum but had a couple of targeted questions.

For context, inside cabin is getting hot air when heat is off after driving for a bit on my 88' 3.2 (manual heat).

My initial suspects were the flapper boxes.
I took a couple of pictures:





1) Can the "overlap" (see lines I drew in red) cause the hot air issue I'm having?
2) Is there a way for me to check that the inside of the flapper box closes without removing it? I understand removing can be a PITA as bolts are prone to breaking.

Thanks all for your help,

[salayc]

The red arrows are not your problem, that's just an area for the hot air to escape when the box is closed. You should remove them so you can look inside and the problem should be obvious. There might be a rebuild kit available somewhere, but otherwise you have to replace them.

[Dan Owens]

Your flapper boxes have a a diaphragm on the inside that closes when the the vent is in the open position to prevent the heated air from flowing into the cabin. often that diaphragm is degraded of rusted out and does not work. See pic I have that same issue. What you can do to temporarily stop the airflow is remove the snorkel tube in the engine bay the goes between the fan and the heat exchanges. See pic That way no air is pushed thru the exchanger and into the cabin

[Solamar]

Maybe it's just obscured in your photos, but it looks like the clamp that holds the Boden cable in place is missing or broken.

Can you visually see the flapper rotate when someone actuates the lever?

[megerian]

Can you manually move to a fully closed position? By fully closed I mean that the external openings are at the maximum opening, and the internal vent is completely closed. I had the exact same problem, and nothing was actually broken or degraded, but rather it was stuck at about 75% closed which was enough to direct plenty of heat into the cabin. I dislodged it manually and that solved the problem.

[mziin]

Thanks all for your replies!!

Next step for me is to take it down so that I can see what's going on with the internal vent.

[rokemester]

Originally Posted by megerian

Can you manually move to a fully closed position? By fully closed I mean that the external openings are at the maximum opening, and the internal vent is completely closed. I had the exact same problem, and nothing was actually broken or degraded, but rather it was stuck at about 75% closed which was enough to direct plenty of heat into the cabin. I dislodged it manually and that solved the problem.

Hmm this thread reminded me of the valves in the flapper boxes. I’m getting some heat in the cabin, and the slots are open but maybe not entirely open, which means the valves may be slightly open allowing heat into cabin.

[smadsen]

I found on my '82, manual heat, that the flapper must completely close and "dump" 100% of the hot air. On a warm day even a small leak on one side will over heat the cabin. I could feel the hot air leaking out the cabin vent on the dash.

I ended up replacing the control cables and working the flapper mechanism with a lot of WD-40. Then adjusting so the flapper valve to close with a slight "ker-thunk."

Also, I'm not sure, but there may have been a rubber gasket around the flapper to assist in sealing. Mine were completely gone, a few rubber remnants laying in the bottom of the box.

[Fleming]

Lossen the orange flex tube clamp, lift off the hose and look inside the valve with a mirror (if needed). No need to remove the valve mounting bolts.

Lubricate and Exercise the flap.

Yes the holder for the bowden cable is missing from one of your valves The bowden cable should be held stationary in place so the wire can move inside it, Compare to the other side - a clamp from the black tube is missing - it should have a small clamp to hold the bowden cable.

HTH

[kltarga72]

I removed the flapper boxes on my 1980 SC and did not have any problem with the bolts breaking. I soaked them with PB Blaster and worked the bolts back and forth. I also have a lift in my garage which made it easy to get to the nuts and bolts. Removing and cleaning the flapper boxes should fix your problem.

[Walt Fricke]

I've always had at least one of the studs break when removing the boxes. Two will still do the job of holding. Otherwise you are faced with improvising something - drilling out the stud and using a nut cert or the like, for instance.

[rokemester]

Originally Posted by Walt Fricke

I've always had at least one of the studs break when removing the boxes. Two will still do the job of holding. Otherwise you are faced with improvising something - drilling out the stud and using a nut cert or the like, for instance.

I don’t think the Porsche engineers envisioned we would be servicing flapper boxes so many years later. I’ve snapped those tender studs as well and wondered why they didn’t come up with a better more easy to service approach.

[Showdown]

I had errant heat in my cabin with the heat levers fully closed. It turned out to be the original plastic lines being degraded and sticky and not allowing the cable to slide consistently. Replacing them ($12) allowed the cable to move freely and close the heater boxes completely. No more 1000 degree air in my cabin in the summer.