NO HEAT blend door access?? - PeachParts Mercedes-Benz Forum

Proctor750 · #1 10-07-2012, 05:51 PM

Figured I would post this in the gas section too..

I have a 12/85 190D, my heat does not work at all.
The pipes leading to, and from the heater core are hot. The heater core itself is hot. All elements of the vacuum actuation function except I am assuming the blend door actuator.
SO I removed the center console, the vent grills, and the glove box to figure out where it was. I see that it sits up inside of a cowling attached to the top of the inside of the dash.

How do I gain access to the blend door and the blend door actuator?
All I can see without taking the entire dash out is the shaft coming up from behind the heater core, and it's support truss as illustrated in the picture below....

I need to access #37.

I'm replacing the dash soon anyway, I am half tempted to just cut a damn square out of the dash.

mbdoc · #2 10-08-2012, 08:42 AM

Removal of dash is required.

If you remove the vacuum line to heater valve, you should have HEAT.

Proctor750 · #3 10-09-2012, 10:03 AM

Quote:

Originally Posted by mbdoc

Removal of dash is required.

If you remove the vacuum line to heater valve, you should have HEAT.

By heater valve you mean blend door actuator? I believe the default is "cold" if it fails.

mbdoc · #4 10-09-2012, 12:00 PM

No, the vacuum operated heater valve, number 41 in your drawing.

Proctor750 · #5 10-14-2012, 09:48 PM

SO I took the dash off and found that the blend door was stuck OPEN and the actuator works fine. This is the exact opposite of what normally happens, as the blend door defaults closed.

I tested the vacuum T to make sure the rubber hasn't shrunk around the soap stone inside to where it couldn't bleed off vacuum anymore, but it tested fine.

What I know: The vacuum to the actuator is constant there is no way to shut it off.

What I want to know: Is this the switchover valve failing and causing the constant vacuum, or is it the push button unit where the temp wheel is located failing? Every function on both items works perfect except being able to stop vacuum to the blend door to let it close..

mbdoc · #6 10-15-2012, 08:36 AM

You would need to test the signal wire from the pushbutton to the switch-over valve for a constant ground signal.

Holmesuser01 · #7 10-15-2012, 08:39 AM

I truly understand your frustrations. I've done this job myself on my '84.

I did my heater core replacement. What a major pain, but once done, that working heater is more wonderful, knowing that I did it myself, and saved about $900 labor.

While I had the heater box out of the car, I cleaned the insides of it thoroughly, and the sealing surfaces, too. Replaced 2 of the little vacuum actuators... the green one on top, and one of the pink ones, as they were not holding vacuum more than a couple of seconds.

No heat? I discovered that the slider switches in the heater control module were coated with years of cigarette smoke and road filth. I cleaned them all with electric contact cleaner, and resoldered the connections on the PC board inside the heater control box, and replaced every electrolytic capacitor on this module... they dry out and go bad after 20-25 years in a hot car!! My whole system came back to life after this work was finished.... No A/C, though, as a previous owner removed the compressor and cut the refrigerant lines out.

I've got an electronics repair background, and know how to troubleshoot. Dont just assume that something is wrong. Throwing parts at it is something I did at first, but stopped, after several times of seeing the problem was no different than before, other than my wallet being a tad lighter.

Proctor750 · #8 10-15-2012, 11:30 AM

Haha previous owner lost my compressor too. Left the lines open and exposed.
I think mbdoc is right in testing for constant gound. Something is telling this actuator to see nonstop vac. At least its narrowed to 2 items. I have the line disconnected from the switchover valve for now and am enjoying the heat