W202 Heat is either hot or cold... no warm

[dude99]

Hey all, Trying to sort out the heat on my GF's 1999 C230 Kompressor. It is the "Classic" trim level so it has the twin temp knobs and the dials for the blower and vents, not the digital climate control system fitted to many of them

The passenger side previously worked fine and the heat modulated as you would expect. The drivers side has always either blown cold or hot, there is no warm section on the dial. Its like it just flips over from full cold to full hot, and now both sides are doing it.

I have disassembled and cleaned the duo valve and it made no difference to the issue. I'm assuming at this point it is working as I can get either hot or cold on each side so the valves must be opening and closing.

If you leave it in the middle section of the dials it will flip flop back and forth, scorching hot for a bit, then cold for a bit with no particular pattern.

I'm assuming at this point that its probably either the control panel itself or a sensor, but I have been unable to find any sort of information on how this system actually functions or what its components are.

Any and all help is appreciated.