[W126 Coupe] Heater stuck in "on" position

[Dick Spellman]

Hi Waldemar:

I'd start with a check of the external foil fuse for the blower and the 
fuse for the ACC.  Next would be the ignition switch.  Is this a 
constant problem or is it sporadic?  For ex. one day you turn on the 
ignition and everything works and the next day you turn the ignition and 
the ACC is dead?  This would be a symptom of the ignition switch 
failing.  Next might be bad solder joints on the ACC head unit harness 
pins.   Then there is the question, does the AC clutch engage for air 
conditioning and you still get hot air?  Then, I'd check the mono-valve 
which may be stuck in the open position allowing engine coolant to flow 
through the heater core and compete with the AC evaporator.   One way to 
clear this would be to place the ACC in MAX AC and see if the stuck mono 
valve plunger frees up.  You could try tapping the mono-valve head as 
well while in Max AC.  Last would be the vacuum elements that could 
allow too much outside air to enter the cabin through the fresh air 
door, defeating the benefit of the AC.

Dick

Waldemar Kalinowski wrote:

> Hi Everyone,
> Heater pumps hot air through the interior vents. Heater blower 
> non-functioning.  None of the climate control buttons work. What would 
> be the order of things to check out? How to disconnect the heater, at 
> least temprarily?. Weather's getting hot in So Cal.
> Thanks for advice.
> Waldemar 1989 560 SEC
>
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