Low dash air flow - PeachParts Mercedes-Benz Forum

300DandTD · #1 08-17-2006, 08:02 AM

I have an 85 300D. The blower motor is good and runs strong and I can see the air flaps control pods cycling but in the heat, defrost or cooling mode I get very weak air flow from the dash. I have an 85 300TD also and the air from the vents is considerable. I have tried everything to remedy this. Can anyone offer any suggestions, or where I might find an isometric of the ventilation flow path ? I hate to take this kind of problem to a dealer.

Hit Man X · #2 08-17-2006, 08:56 AM

Does it seem most of the air is blowing out of the defroster vents?

JEREMYC · #3 08-17-2006, 09:05 AM

What all have you tried to remedy this? My guess is it would be the vacuum pod in the center of the dash. The rubber diaphram in those pods can crack and let vacuum leak through causing the vent blend door not to close and allowing air to bypass to places you do not want it.

Mismost · #4 08-17-2006, 10:26 AM

does sound your center vent is not closing/opening the flap for the vents....bet you have great defrost air! Mine did the same thing and to fix that seems to require removing the dash...I passed on that option and plugged the vac line to the pod, and super glued the flap so I always have center vent airflow....in short, I hacked it!

winmutt · #5 08-17-2006, 11:19 AM

Quote:

Originally Posted by Mismost

does sound your center vent is not closing/opening the flap for the vents....bet you have great defrost air! Mine did the same thing and to fix that seems to require removing the dash...I passed on that option and plugged the vac line to the pod, and super glued the flap so I always have center vent airflow....in short, I hacked it!

Is it possible to do this hack with out taking the dash off?

Mismost · #6 08-17-2006, 12:01 PM

winmutt...yes it is. remove the pass side kick panel, find the vac line to the center pod and plug it. use a long screw driver inserted thru the center vent to operate that flap while looking at the side of the air box from the pass side. You will see a white "button" looking thing that is the flap pivot point...study it while operating the flap with the fan on and you'll see what and where to super glue....just be sure you KNOW where the flap is when you glue because that is where that flap will stay from now on!

I also did a vacumm line mod that closes the fresh air door when the A/C is on....that helped a lot too...no longer cooling 20% outside air all the time, which is tough in 100+ days.

Mismost · #7 08-17-2006, 12:06 PM

here's the link to the fresh air door mod

A/C fresh air

300DandTD · #8 08-17-2006, 12:22 PM

Thanks for all the replies. I have done the following: cleaned the evaporator (kind of) checked all of the pods operation, the center air supply flap seems to cycle as expected, system vacuum checks, replaced blower, checked air supply grids and what I could see into the plenum. It sure seems like the blower is running normally but just not moving any air. I will try your suggestions. Thanks.

300DandTD · #9 08-22-2006, 11:32 AM

If the main air door was failed closed would this not allow the blower to move much air ? Does the air flow go through the evaporator at all times with cooling only when compressor is selected with CCU ? Sure wish that I could find a visual of the air flow through the system on a 123.

#10 08-22-2006, 11:53 AM

Don't know if this will help...

http://mb.braingears.com/123_DISK2/program/matrix6.htm

JEREMYC · #11 08-22-2006, 02:47 PM

Mine was blowing a lot of air out of the defroster vents. The pod that controls the opening or closing of the defroster vent on my 83 300CD is in the drivers leg room area just in front of the console area. It is the one that sits vertical. Mine would just barely move when I pressed the defrost button. I closed it completely and zip tied it closed until I can fix it correctly. It sure made a big difference on the air flow.

rhodes2010 · #12 08-22-2006, 02:57 PM

Left side panel covering tunnel (drivers side kick panel) - remove it.
And the hush panel below the dash/steering column.

Pod that has two vacuum hoses and is vertical right above gas pedal area.
Linkage comes out the top.

With car running and fan at full reach up in there and pull that linkage down
and close that flap. If your vacuum pod is broken like mine was than your
forceful dash air was blowing out the defroster vent. Like Hit Man X asked.

If you can pull it down and the dash starts to blow hard.....
then replace that pod.
No dash removal necessary.
Although I did this with a strange variety of tools and patience it was done without removing instrument cluster.
If I ever do it again I will remove the instrument cluster to get at the pod
connectors which face up.

Good Luck.

It worked for me and I now have a nice strong dash air flow.
I also took the time to remove the glovebox and reach into the center pod and
used a paper clip like wire (made from music/piano wire) to wire that center flap open.
This gives me a stronger flow out of center on vent setting and lets me control it with the control knobs on the vents.

redassag00 · #13 08-22-2006, 03:44 PM

Quote:

Originally Posted by rhodes2010

Left side panel covering tunnel (drivers side kick panel) - remove it.
And the hush panel below the dash/steering column.

Pod that has two vacuum hoses and is vertical right above gas pedal area.
Linkage comes out the top.

With car running and fan at full reach up in there and pull that linkage down
and close that flap. If your vacuum pod is broken like mine was than your
forceful dash air was blowing out the defroster vent. Like Hit Man X asked.

If you can pull it down and the dash starts to blow hard.....
then replace that pod.
No dash removal necessary.
Although I did this with a strange variety of tools and patience it was done without removing instrument cluster.
If I ever do it again I will remove the instrument cluster to get at the pod
connectors which face up.

Good Luck.

It worked for me and I now have a nice strong dash air flow.
I also took the time to remove the glovebox and reach into the center pod and
used a paper clip like wire (made from music/piano wire) to wire that center flap open.
This gives me a stronger flow out of center on vent setting and lets me control it with the control knobs on the vents.

I used a zip tie to hold that one down (under driver side) and I get PLENTY of air flow.

Also, I had issues with the BLower motor, I bought Kent's guide to replacing the brushes, which made the blower worse actually, so I bought a new Blower motor and now, theres PLENTY of breeze going thru there!

300DandTD · #14 08-23-2006, 11:40 AM

Very good ideas gentlemen. The car in question comes home this weekend with a son so quess where I will be all weekend !!!

greasyv · #15 08-24-2006, 12:48 PM

just fixed (rigged) mine today thanx to reading this thread. Probably not perfect but at least my center vents blow cold air now. I didn't take the time to mess with the fresh air inlet vac lines. will save that for another day.

On an 85 300 td the vac pod (pink) is horizontally mounted right behind the center vents. the easy way to get to it (if you call it easy) is to remove the glove box. I also removed the passenger side center vent and vent boot to help access the pod. no need to mess with anything on the drivers side kick panel on this car.....