Climate Control/Blower Regulator Help - PeachParts Mercedes-Benz Forum

IanJ · #1 08-29-2006, 11:05 PM

I'm trying to diagnose what I believe is multiple problems with the climate control on a '85 300D that I recently acquired. When I got the car the climate control was all screwed up. The blower would run when climate control was set to off, but only on high speed... and turn off when on EC....otherwise always in defrost mode. I pulled the climate control unit and found a circuit in it to be burnt/broken. I carfully soldered a jumper over the burnt circuit, but when I plugged it in another circuit started smoking and burnt through. I have a replacement control unit now, but I'm afraid to plug it in until I'm sure some other problems aren't frying the control unit.

While searching for wiring problems I found that the blower regulator was cracked and partially out of the housing.

Is there a way to test the blower regulator? (anybody have a used one?)
Any ideas what could fry a climate control unit or is this likely caused by an internal short in the unit?

Sorry about the long post... but any help would be appreciated.

#2 08-29-2006, 11:18 PM

It seems likely that the blower regulator could be doing it if it's shorted. You should be able to find a used one in a junk yard, eBay, etc.

Also, the auxiliary water pump or the blower motor itself can toast the control unit if they are drawing too much current. Consider testing them individually before you install the control unit.

mplafleur · #3 08-30-2006, 06:42 AM

The blower motor can't cause a problem with the push button controller. The PB controller sends a signal to a blower control module and it is the one that drives the motor. 0 volts = off and 12 volts = full speed, and there are various points in between that give you the other speeds.

I'd look at that aux water pump..

#4 08-30-2006, 08:56 AM

Quote:

Originally Posted by mplafleur

The blower motor can't cause a problem with the push button controller. The PB controller sends a signal to a blower control module and it is the one that drives the motor. 0 volts = off and 12 volts = full speed, and there are various points in between that give you the other speeds.

I'd look at that aux water pump..

That sounds reasonable, but the guys from GDL specifically told me that a bad blower motor would damage the CCU.

jshadows · #5 08-30-2006, 09:03 AM

seems like the blower would hose the blower regulator before it got to the CCU. I don't think there's a direct connection between the blower and the CCU. everything goes through the regulator (and the toaster).

#6 08-30-2006, 10:23 AM

Quote:

Originally Posted by jshadows

seems like the blower would hose the blower regulator before it got to the CCU. I don't think there's a direct connection between the blower and the CCU. everything goes through the regulator (and the toaster).

Correct, the regulator is located between the CCU and the blower motor in the circuit. However, their location in the circuit has nothing to do with which one would fail first due to high current. There is no fuse anyplace between the CCU and the motor, and experience seems to indicate that it's the CCU that gets fried most of the time. In my case, the CCU was cooked and the regulator was OK. I just replaced the blower motor and the CCU, and all was well.

IanJ · #7 08-30-2006, 10:57 PM

Quote:

Originally Posted by jshadows

seems like the blower would hose the blower regulator before it got to the CCU. I don't think there's a direct connection between the blower and the CCU. everything goes through the regulator (and the toaster).

When you refer to "the toaster", I assume you are talking about the blower motor resistor on the wheel well? Could this be part of the problem as well? I would think that if it failed, the blower just wouldn't work at all?

IanJ · #8 08-30-2006, 07:58 PM

Please excuse my ignorance, as I'm not much of an electrical person. The blower would work, but only on high speed... wouldn't that indicate that the blower is not shorted out? How would I verify that the blower isn't shorted out? I've pulled the blower and it's one of the siemens units that you have to pull the blower cage to get to the brushes.

Thanks for the help!