heating system - am i missing something??

i have a 87 coupe with the auto heat control in the center and after some excitement with the wiper mechanism i am taking the oppertunity to sort out the heating system.
All the valves and control cables at the front are working perfectly.
when i put the centre dial to heat the rear fan starts and the valve in the rear wheel arch closes (well it does now anyway its now clean and freshly lubed)and i get heat. when i put the dial to position 1 the fan stays on and the vents in the wheel arch open (wel 3/4 of posible open area, cand adjust cable as nuts rusted completly) and i get no heat (if i am parked) when i put it to position 0 off again valves are open and the fan in rear shuts off.

my problem is when driving with the dial at 0 i still get heat - the car seems to suck the hot air into the cabin!.

do they all do that or am i missing a set of valves / controls that should shut off heat???

any help greatly appreciated.

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mike 87 coupe'

the valves that you see in the rear also have a valve inside them. if that's not completely closed, you will get heat into the car. when the outer, vaned, valve is fully open, the inside valve should be fully closed. perhaps the valve unit is too rusty to work right.

ah ha
thank for the info john - invaluable!!

The valves only open 3/4 way, is there any otherway to adjust cable at control box end?? if not i will have to go in search of oxy torch to free those nuts.

thanks again

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mike 87 coupe'

[This message has been edited by D911_MEE (edited 04-15-2001).]

Just had a look at pelicans catalog is seems those "flapper boxes" should have a spring, mine dont and i preume the spring pulls them into the open position.

am i right in thinking that it is the spring i need and not a readjust of cable?


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mike 87 coupe'

the spring helps, but the cable should be just slack enough to allow the valve to relax at the fully open position. you may be able to loosen the clamp around the hose and rotate, or slide it a bit. if you just crank on the cable clamp until it breaks, you can just replace the clamps.(put a 7mm box wrench on the bolt head so you don't twist the cable) (step bolt, 2 washers, and a nut).

[This message has been edited by john walker's workshop (edited 04-15-2001).]

cable is loose to allow vale to fully open already, i take it if i get some springs and the valve is still ok its sorted!!. i will prey to the porsche Gods tonight!!

thanks again john.



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mike 87 coupe'

John Walker, Thanks.
I was planning to ask if a non closing valve in my heater box might explain why I am getting heat with the lever between the seats full down.
Now I know! the valve must not be closing fully. Will look at it with a mirror and dink with it with the control cable disconnected to see what I have.
Thanks, Ned Monaghan

If both flappers are not closing completely you might be able to cure the problem by adjusting the rod inside the control box (between the seats), but the problem is probably the flapper box itself.

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1984 911 Targa
1986 911 Coupe