The climate control system in my 1987 300TDT seems to be operating improperly since I cannot get heated air out of the footwell flaps.

I have searched for posts on climate control problems like mine, but I haven't found one yet with symptoms like mine.

When the system goes into heat mode (temp dial between 22 and 18, EC button pressed, fan on auto, outside air at 55 degrees F)), the air seems to only come out of the defrost vents and the lateral vents on the ends of the dash. The climate control (ACC) seems to switch between full heat out the defroster and lateral vents and cool air from the center and lateral vents to try and keep the interior temp at the right temp. The ACC doesn't seem want to use a medium fan setting with only warm air for some reason.

Placing the temperature dial at max with the solid down arrow and outline up arrow button pressed (with or without EC marking), and the fan button at auto seems to make no difference, the air still comes out of the defrost and lateral vents.

Additional info:

The fan operates properly at min, max, and auto when pressing each of the buttons.

Occasionally when I turn the climate control on, I can hear a faint clicking sound from behind the glove box area and nothing happens initially until after 5 or 10 seconds. There are also occasions when I press the off button, and the climate control system runs for about 15 seconds, and then it shuts off.

The only time I am able to get air out of the footwell vents is when I press the button with the solid up and down arrows.

I have tested all of the vacuum pods and they all hold 15 in Hg of vaccum except the center vent pod. I have also swapped the hoses for center vent pod and the air diverter flap pod to get air around the bad center vent pod temporarily.

The air sample fan is working properly since it seems to hold a small square of paper at it's intake point on the dome light.

I have the MBZ Climate Control Service Manual, and I have run the functional tests and based on the results the manual says to run the electrical component test which seems to require a special test instrument/breakout box.

Does anyone have any ideas on what component might be bad? At this point it looks like it might be the control unit, but I need to run more tests. Any thoughts and ideas are welcome.

Thanks in advance.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed