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1987 300TD: Defroster troubleshooting

848 views 10 replies 3 participants last post by  Casanova* 
#1 ·
I'm trying to understand why my defroster is not working properly. The driver side defrost vents supply no air. The passenger side defrost vents however seem to be fine. Also the side dash vents on both the driver and passenger sides seem to be fine. Could this be an issue with the vacuum pods that operate the vent flaps? Something else?
 
#3 ·
#5 ·
OK, found another good thread (W124 climate control vacuum pod replacement - PeachParts Mercedes ShopForum) and may have answered my own question. According to that post, the side vents are always open, which would explain why they have plenty of airflow.

So I'll go ahead and order a new pod for the defrost vents (part # 124-800-00-75). Not sure if I will bother replacing all of the pods because from what I understand the defrost one is accessible by removing only the glove-box, whereas the others are accessible only after removing the whole dash...
 
#6 ·
Jayare, didn't see your post before I posted. Yes, that's true. The fact that the passenger side defrost is fine might mean a supply tube has come loose, as you are saying. Not sure where I would start on that though... Never had any work done under the dash as far as I know...
 
#8 ·
OK 1 month later and I'm finally getting around to this :)

I pulled the glove box this morning and had a look. You can see the attached photo. The defroster pod has actually been disconnected from the black plastic lever that control the defrost vent. The black plastic lever has been manually placed in the closed position and held there by a thin metal wire. Also, the port #1 has been plugged and the red hose that would normally go there can be seen disconnected.

Someone has obviously been in there at some point but I'm not quite sure what they were trying to sort out. Probably the defroster pod was not working causing it to hold its default open position - meaning all defrost when the fan is turned on. Rather than repair or replace they decided instead to disconnect the pod and have the vent always closed. Not sure what to make of port #1 and wondering if it's somehow related. I've read that ports #1 and #3 control the re-circulation vents.

Anyone have any insight on what might be going on here? Any advice on how to proceed? Thanks!
 

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#9 ·
Had some turkey and a nap (happy thanksgiving!) and then was back on the car this afternoon.

I removed the little wire (not supposed to be there) and then watched the pod with the car running and the defrost button switched on and off. I was expecting the metal connecting rod to pull back when the defrost was switched off but there was no movement. I figured this meant I had a bad pod.

Replaced the pod with a new one as shown in the attached photo. Connecting it properly to the black plastic lever of course moves the lever to the default open position. Ran the car again and played with the control settings. Now it seems I am only getting defrost, no matter what settings. In other words, the defrost pod (which is brand new) is not being actuated.

Does this mean I have a bad line to the pod? Or could it be something else?
 

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#10 ·
disconnect the line, hook up a mityvac to the pod, and see if it actuates when you pump it down.

connect the mityvac-with-gauge to the vacuum line, cycle the controls, see if you get vacuum when you expect the defroster to open (or close, I dunno which way it goes).

if you don't have a mityvac, get one. they are extremely useful for this sort of thing.
 
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