Heater tap

[Testie]

1073 SL350 W107. Does anyone have a simple diagram for the vacuum lines from the vacuum tank to the levers and back to the actuators and on to the heater tap?
All the diagrams that I have found on the web are unclear. The tap has been converted to single pipe type with the green hose being plunged up (with golf tee) but still the tap opens at various times, usually on demist.
Any help appreciated.
Col

[Chai]

When the vacuum line to the tap has vacuum, the heater tap is on the OFF position - stopping hot water from flowing.
When there is little/no vacuum in that line, the tap is ON - allowing water to flow through the heater coils.

The heater levers on the control panel are used to both: (a) open the hot air flap at the left or right side depending on the lever moved; and (b) to allow air to leak into the vacuum line when the lever is in the up position.

Moving either of the heater levers up will cause air to leak in the line.

[Chai]

This weekend, I discovered a 'strange' thing. I've previously physically disconnected the rod from the vacuum element to the lever for the heater tap and moved the lever to the OFF position in an attempt to stop warm air coming out of the vents.

However, when I removed the glovebox (is a RHD car) to check the vacuum element that opens/shuts the recirculating air flap, I noticed that the hot water pipe at the interior side of the firewall either leading to or coming from the heater box was hot even when the heater tap was fully shut off.

Before the heater vacuum tap was replaced several years, I recall blowing through the water pipe in new tap and no air would pass through when the tap was at the off position.

01 heater tap in open position.jpg

I removed the water hose to the tap (is higher than the engine/radiator so very little coolant loss) and used a video scope to look inside. This confirmed the heater tap lever still works. Why is the water pipe hot even though no water should be passing through it?
Is it because the tap is downstream of the hot water supply side?

02 heater tap internal - open position.jpg

03 heater tap internal - partially closed position.jpg

04 heater tap internal - fully closed position.jpg

[Chai]

This picture shows the hot water pipe behind the glove box.

Behind the glovebox.jpg

[CraigB]

But guessing not blowing hot air? Just guessing, but I am thinking there is water both sides of the tap still and conduction would transfer heat but the core in the heater would cool any of that conducted heat more than could heat any air going through it, but the pipe itself could still be hot. Just thinking about it logically and sharing thoughts.... someone else's turn!

[Aussiemerc 3]

But guessing not blowing hot air? Just guessing, but I am thinking there is water both sides of the tap still and conduction would transfer heat but the core in the heater would cool any of that conducted heat more than could heat any air going through it, but the pipe itself could still be hot. Just thinking about it logically and sharing thoughts.... someone else's turn!

Did you solve your problem? Been a while since I visited this forum.

The taps can fail with the result that heat continues.

[Chai]

Craig's explanation is likely right as an operating tap only stops the flow of hot water. The heat can still conduct through from the other side of the water circuit but that only heats up the incoming air a little.
With the ventilation inlet also drawing in air that has been warmed by the engine, especially when the car is moving slowly through traffic, this means the air coming out from the vents always feels warmer than ambient temperature.