Another W124 Climate (Un-)Control Problem
 

Hey folks,

I've been trying to diagnose a nagging problem with my climate control. With summer on its way here in the Great White North, I've just noticed that my vents are now putting out constant heat. The flow is low at idle and increases with the speed of the car. Here is a brief history of what's been done previously, although sorta unrelated to this problem:

1) Blower motor replacement (seized/would not turn; 1.5 years ago).
2) Auxiliary Water Pump (Leaking; 1 year ago).
3) Coolant flush ( <1 year ago)
4) Auxiliary Fan (was blowing fuse D, until I discovered the motor had seized 1 week ago)
5) Resoldered Push Button Unit today to attempt to alleviate. Fixed the previously unresponsive Defrost mode.

Symptoms:

1) Push Button Unit (PBU) responds normally with the key turned to first stop.
2) PBU intermittantly responds when vehicle is started.
3) Temperature Dial has no effect when vehicle is running, but works when vehicle is not.
4) A clicking noise comes from glove while the car is running and PBU is set to any position. Interval between clicks is every 25 s. +/- 1 s. Noise is the same as when switching modes.
5) If the key is turned while the blower is set to ON, the warning buzzer volume noticeably drops.

Hope this is enough, to get the ball rolling. As a side note the A/C does not function on this car, I dislike it which is why I have not gotten around to fixing it.

My 1987 300E thanks you in advance.

Sounds like the water valve is not being controlled or doesn't rrespond to control. It takes power and ground to shut the valve... check it out.

I will test the valve soon and post my results. I have taken this valve apart recently as I thought it may be the culprit and the diaphragm appeared to be intact. Could a misbehaving water valve be responsible for the unresponsive PBU as well?

Thanks

From your test results I get no feel for whats happening. You state: "Temperature Dial has no effect when vehicle is running, but works when vehicle is not." Describe how the temp dial works when not running. Does the heta go away?

Very little of what I expect to happen with changes in the temp wheel will work with the engine not running.