Driver side footwell heater stuck on

[zenithblue71T]

Hi guys,

My driver side footwell is blowing molten hot air on my left foot while I drive and I can't shut it off. My heater lever is down and my heater knob is all the way to the left. The passenger side is not blowing hot air nor are the defrost vents on the dash. If I move the vent direct knob to full defrost, it still gets hot down low. [update, if I move red lever to the right, it directs the heat up top]. What do you recommend?

Could the heater valve be stuck open or closed?

I have a stockish 1971 911T with SSi heat exchangers and original vent boxes with new orange heater hoses replaced a few years back.

[xpensivewino]

The only way I can see that happening is that the heater flapper box is stuck in the open position. The cable may have come undone on that side. My guess is when you actuated the heater the cable popped off the valve. If you jack the car up and check that valve you may see the cable is loose at the valve. It’s possible it came undone on the cockpit end, but more likely at the valve... Steve

[gled49]

Box is stuck open. Maybe Bowden tube slipped off flapper and is wedged open. Broken cable will default closed with help of spring.

[zenithblue71T]

And the heater valve link I posted is what I need to inspect, yes?

[xpensivewino]

Yes that is the item to inspect.

[30westrob]

Very common problem. I suggest you jack the side of the car enough to get your arm under and your hand up to the valve. With your hand you can rotate the valve so that the bottom slots are full open, closing off heat from entering the cabin. The valves stick due to corosion. Replace or clean and lube are the only long term solution. Rob

[zenithblue71T]

Bad news. I replaced the heater flapper boxes with SSI heater flap boxes. Replaced the cable and still the heat is coming through the dash. I can direct the heat up to the windshield or down to my feet. The faster I drive, the more it comes through and hotter it gets. WTF could be wrong here?

[mac73s]

Since you replaced the heater valve(s) and had to undo and reconnect the heater level wires to each of them, haveyou confirmed that the valves are in their fully open position (as illustrated in the above photo you provided) when your heat lever is all the way down? If they are, then this is indeed a mystery.

[xpensivewino]

The 356/911 heat system is as rudimentary as it gets. The heat can only get to the cabin via the valves pictured above. The valve is either open or closed. It should be very easy to figure out the issue. No chance you have a webasto gas heater in the smugglers box?