1991 350SD Heater A/C Problem

[pbrandon33@char]

The heater and A/C does not work in my 1991 350SD. The heat comes through the system, but the blower does not work. The blower motor has been tested and it is O.K.. The A/C compressor does not work. The fuses have been checked. Could this problem be the switches in the dash?

Thanks in advance for any suggestions.

pbrandon33@char

[burntcloth]

I had a similar problem and don't know how closely related our two cars are, but mine was caused by cracked solder joints in the switch module.

Pulled the switch module apart and the circuit boards meet at right angles, hit the right angle solder joints with a soldering iron and the whole thing worked again! Had I taken it to a mechanic, they would have replaced the unit ($500, I believe!) That's why I love these forums.

[wgilmore]

Originally Posted by pbrandon33@char

The heater and A/C does not work in my 1991 350SD. The heat comes through the system, but the blower does not work. The blower motor has been tested and it is O.K.. The A/C compressor does not work. The fuses have been checked. Could this problem be the switches in the dash?

Thanks in advance for any suggestions.

pbrandon33@char

Might be the switches in the dash , but I would check a couple of other things before that. This series has a neat little Bosch proprietary thyristor fan speed controller that can cause the blower not to come on when you want heat. It sometimes defaults to some arbitrary speed but can completely stop.
When you say the compressor does not work, does the compressor clutch engage?
There is a speed sensor for the compressor that has to feed back to the control to allow the clutch to engage.
There are temp sensors and all sorts of things talking to the dash control.
Then there is the Klima or MAS relay to look at too.

Good link to read below -

http://www.peachparts.com/Wikka/AcDiags