rbeggs

My heater will randomly stop providing the variable temperature function.
There will be off (blue dot) and on (red dot) and nothing in between.

I can jolt it back to normal functioning by blipping the defrost mode on and off. It will then function normally till the next time it decides to go south. Once functioning correctly, it will continue to do so as long as the car is running. At some point, one or six startups latter it will fail again and I have to resort to the defrost button shock treatment. I suppose it could be something as pedestrian as cold joints on the the PC board that are stressed back into functioning when I flex the switch. I'm looking for something more interesting though.

What particular interaction of solenoids, valves, flaps, vacuum action and button switching would cause this behavior?

Thanks,

RB