Intermittent uncontrolable heat '98 ML320 - PeachParts Mercedes-Benz Forum

riske · #1 04-16-2007, 09:34 PM

The temperature of the air coming from the vents in my ML320 is out of control. It cycles intermittently from hot to luke warm when the dial setting is on cold. It usually ends up as hot and stays there regardless of the dial setting.
IN AN OLD THREAD , MB DOC said........"Welcolme......
The early ML uses a blend air system..no heater valve. Also no diagnostic abilities on that early system.

There are 4 possibilities for your problem..YOU will have a hard time trying to figure out which one will rectify the problem.

The in-car temp sensor
the control unit in dash
the blend air motor &
the blend air control unit.

ANY of those could cause an intermittent problem like you are having...."

MY QUESTION IS:
How can I diagnose which component is causing the problem?
THANKS

mbdoc · #2 04-17-2007, 08:05 AM

That system on the 1998-01 ML's requires replacement or substitution of those components to solve the problem.....

Do you here any clicking noises behind the dashboard??

riske · #3 04-17-2007, 10:09 AM

There is no clicking noise. I know where the air blend motor is located .
I believe that the temp sensor is a small bulb which is located located behind the slots directly under the low range switch.The control unit in the dash is the whole assembly with the temp and fan control knobs,correct? And , the
blend air control unit is the part which the blend air motor is attached to, right? HAVE I CORRECTLY IDENTIFIED THESE CONPONENTS ?
I thought that I would remove the upper dash and take out the air blend motor first and check the blend mechinism for binding or stiffness, and then see if the motor itself works as I change the temp setting with the dial. DOES THIS SOUND LIKE A VALID TEST? I hate to just start buying parts till I find the faulty conponent. THANKS DOC