Flashing Heater Controls!

[GeoffBW]

Can anyone tell me why the fan and direction control knobs on my 1996 C250D are flashing?
Thought I had a problem with the duo valve i.e. full on heat from both sides, although the fault is intermittent - sometimes OK, sometimes fails during a trip. Have now noticed that when the heat is full on, the heater controls flash. Unless the headlights are on - in which case the heater controls are not lit at all and the panel lights maintain their brighter daylight setting.
When the heater is under control there is no problem with the panel lights.
Is this still likely to be a duo valve problem or is it more likely to be the heater controls?
Thanks
Geoff

 

[television]

Never heard of that one Geoff, I would think that the control box is under load when the duo valve sticks, most things flash when there is a fault

 

[bigasotonuk]

Hi,
I personally think your problem is in your heater control unit, though why the lights don,t flash all of the time i don,t know.
The alledged fault with your duo valve could very well be your control unit and not your duo valve, if you control unit does,nt send a voltage to your duo valve it will automatically default to max heat as your car is at the moment, though intermittently.

 

[GeoffBW]

Thanks for the advice.
Replaced heater control unit and everything now seems to be OK.
Geoff

 

[bigasotonuk]

Hi,
Glad its all sorted out. Thanks for the feedback, did you source a second hand one?

 

[GeoffBW]

Flashing Heater Controls - Part 2

Fitted a second hand control unit which sorted the problem but only for a couple of hundred miles. Heater controls then reverted again to flashing with no control over heating temperature. (Lucky it's hardly been above zero outdoors since!).
Have today changed the duo-valve but problem remains.
Is it possible that some sort of duo-valve fault screwed the first control unit and then did the same to the replacement?
Has anyone got any better ideas than changing the control unit (again).
Thanks,
Geoff

 

[television]

I will have a look later to see what is involved, but I have my own problems today

 

[GeoffBW]

thank you Malcolm