I just solved exact same problem. Two things contributed to malfunction. The temp sensor next to my sun roof control was clogged but mainly the problem was in the temperature control module.
The temperature control wheel is attached to a rheostat that controls the temperature settings. The pins from the rheostats (twins sitting side by side... one hot the other cold) can crack at the solder points and become disconnected from the circuit board. If this is the case you will see the crack around the pin where it is soldered to the circuit on the board.
Either resolder the crack or solder a thin wire from the cracked pin to another pin on the same CIRCUIT of the board.
If you are able to do this repair I will tell you how to take the control module out and then disassemble it.
Otherwise buy a new module from parts Shop. Not cheap.
1993 190E 2.3
2000 Toyota 4x4 Tundra
Last edited by ejsharp; 09-01-2002 at 11:41 AM.