1989 E34 535iSE Manual. 248K miles.
Has anyone any ideas on this fault:
Heater blows hot air all the time unless fan is switched off on the heater controls. I then can't get any cold air so I cook in the car! Doesn't matter what settings you select on any of the controls, it stays hot.
Have replaced the Heater control panel, model is the automatic version with seperate left\right edge controls and loads of push buttons.
Heater valves replaced.
Has spent hours hooked up to the BMW diagnostic system at my dealer and they cannot find the faults.
If I isolate the heater valve electrical supply on the valves themselves and feed 12v direct from another source then they switch off OK and the heater core goes cold. Wiring to the valves has been checked using the BMW diagnostic system and is OK.
On the verge of total hair loss over this................