galaxie5004

Hi folks.
1st post here.
Trying to diagnose issues with my pal’s ‘92 C4 cab heater system. It’s a non A/C UK rhd car
Heat is coming through into the cabin all the time no matter what position temperatures, sliders and fan controls are in. I’m pretty sure the servos are all seized but during the hot weather I’d like to divert the heat exchanger air away from the rear flap valves as I believe they are both seized so allowing hot exhaust heated air into the sill tubes and forward to the cabin.
1)Can I simply disconnect the tubes and seal off the valves?
2) I’ve seen a page on rennlist that describes removing the top cover of the fan housing under the hood to determine the heater flap position; very tight to remove clips but possible.
How would one replace these clips to secure the housing back though??
Thanks for any advice.
PR

Laker

1) I would disconnect the flapper arm from the servo motor and leave it disconnected and shut.
2) I had no problems removing, repairing and replacing the servos. I used fine emery paper on the contacts inside the servo and they have been fine since.

Great details here: (copy and paste the link) https://web.archive.org/web/20080512024142fw_/http://www.porsche964.co.uk/technical/climate.htm

Good luck,
Laker

galaxie5004

Thanks for your speedy reply Laker!
I think popping off the arm from the servos is a good idea but heat is still blasting through from the heat exchangers in front of the exhausts so I was wondering if anyone has simply removed the flexi pipes and blocked the flapper valves at the rear?
Thanks again.
PR

JohnK964

The differential pressure when the servos close then cause the flapper valves to open is how I understand it works

JohnK964

There is a plastic cover over this area. You can watch the servos move if the are operable the picture is from Begvill’s web sight. It has a good description on how the system works. I supppse sure you could disconnect the hose from the flapper valves

galaxie5004

I believe my flaps are in fact seized!
I’ve made a brief attempt to remove them but the top nut is especially awkward.
Any hints on removing them anyone?

gregmitch

Yes you can remove the hose going from the heatexchanger to the flapper box. I did that a few weeks ago and sealed up the flapper box opening with aluminum tape and now no more heat into the cabin.
If you don't need heat, that's the easiest option. I was getting heat all the time on the passenger side and found that the flapper box wasn't closing. Rather than repair now in the summer, I just decided to remove the hose...seasonal fix.

JasonAndreas

If you disconnect the arm from the servo you will still get hot air leaking past the mixing chamber door and into the cabin, BTDT. You want to close the door, leave the servo physically attached and disconnect the electrical plug connector from the servo.

galaxie5004

I think I’ll seal the ends of the flapper valve for now; Laker recently sealed one of his as a temporary fix. Removing the flapper ought to be easy but access to the top nut would be if my hands were the size of a 5 year olds. I haven’t actually attempted removal yet but anyone done it?
Any tips?

Thank you everyone who’s contributed to this chat so far. Very grateful for all your information and input.
Rennlist is the best!

964George

You may also have damaged paper tubing in the front footwells behind the kick panels.
This will allow hot air to escape into the cabin before it reaches the HVAC unit and your desired settings!

galaxie5004

Hi George
That Sir is a very good shout indeed. I’ll check the hoses behind the kick panels later.
Many thanks for your input.
PR

galaxie5004

Had a few hours today to get under my buddy’s car and disconnect the flapper valve tubing and seal it up with metal tape. I’ve removed the flexi pipe altogether and using one of the large round Jubilee clips fixed metal tape to it and then clamped it back on the forward section of the flapper assembly.
Yet, still getting hot air into the cabin! From where??
It’s substantially better but still getting hot air from centre vents, much less from sides.
Really confused. Thought I’d solved this one!

Rocket Rob

There are two flex hoses connecting the exhaust heat exchangers to the cabin. Did you disconnect both?

galaxie5004

I did Sir!
Both now sitting in my garage.
I just don’t understand where heat could be coming from now the hot air entry point to the system is blanked off!

galaxie5004

Hello again.
Still having overheated cabin issues with the 964 convertible despite removing both flexi tubes from heat exchanger to both flapper valves and blanking off these flapper valves with aluminium tape. I cannot understand how any heated air is entering the cabin!

Any ideas gang?!
Many thanks
PR