I need help tracking down or diagnosing a heating problem
If I have the Rotary dial set at Max heat, and the EC button depressed, I
get a bit of heat from the bottom vents, If I select either full defrost or
the complete up and down setting it blows mostly cold air. Could this be the
control unit? Is there a simple troubleshooting procedure that I could use
to eliminate possible causes one at a time?
This problem seems to be intermittent along with the high pithed squeal that
I have been hearing
Any help or pointers are very much appreciated
Defrost IS the diagnostic. If it doesn't blow lots of hot air then, it's
It's full heat on, full blower un, upward windscreen vents open.
I'm tempted to say monovalve:
But because you can get both hot air and cold air, maybe not, usually (USUALLY(
it failed stuck open or closed but seldom varying. But it is possible. The mono
valve controls the temperature of the water reaching the hater core by being
pulsw width modulated by a controller near the blower which is told what to
do by the pushbutton assembly.
At this age you probabky want to replace the monovalve anyway - the insert is
cheap and that rubber bit is about worn out anyway.
If that doesn't fix it (it might) then find a good used pushbutton assembly
as 99% of the problems with heat in these chassis is that wretched thing. I've
never seen any car that had any other problem with any other bit of this one of
most arcane and overcomplicated heating systems. Keep in mind the manual for the
is larger than the manaul for the entire engine/chassis.
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
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