Burned climate control unit

[dds28]

Recently I had the ignition key on position 2 while doing some diagnostic work. The climate control was off. After about 8-10 min the climate control started smoking. I quickly turned off the ignition and found part of the outer casing melted. What could have caused this? Prior to this, the fan and controls were working normally.

 

[gsxr]

Check the auxiliary pump and monovalve for abnormal current draw... otherwise you might need to perform an autopsy on the control unit. I'm not sure what else can have a large current draw through the unit.

 

[dds28]

Thanks for the reply Dave. Could a bad relay or blower resistor do that with the unit off?

 

[gsxr]

Thanks for the reply Dave. Could a bad relay or blower resistor do that with the unit off?

I don't think so, at least not under normal circumstances, as the blower regulator only receives a control voltage from the pushbutton unit.

 

[Jlaa]

Recently I had the ignition key on position 2 while doing some diagnostic work. The climate control was off. After about 8-10 min the climate control started smoking. I quickly turned off the ignition and found part of the outer casing melted. What could have caused this? Prior to this, the fan and controls were working normally.

If I recall correctly, @a777fan experienced the same "PBU Chernobyl-meltdown" problem with his climate control. I believe he traced the problem back to a faulty regulator. Start here: OWNER - a777fan (E420) | Owners and Their Cars

 

[gsxr]

Jlaa, your memory is amazing. I had completely forgotten about Jon's melty PBU. Posts 662-673 seem to indicate the monovalve was the root cause of his failure. Those posts also have data for measuring the monovalve & aux pump with an ohm meter.

Jlaa -->

 

[a777fan]

Yes! It was the monovalve at fault in my situation. Pretty much 0 ohm-age when tested with a multimeter. Great memory @Jlaa !

 

[dds28]

Thanks everyone for the advice. I will check out the monovalve. After reading the long thread, I also have the fuel relay ticking that can be heard when the car is idling. It is a really fast ticking sound from under the rear passenger seat. I have the original LH module. I currently have a WOT LH module from a 92 model I believe that I bought from a forum member for my 95 e420. I'll swap it out to see if that solves the problem