This past summer I removed the dash and replaced all the vacuum pods, rebuilt the vacuum pump and checked the valve solenoids on the passenger side footwell on my 300sd. The climate control unit is original and appears to be in working order.

Now that its cold out I was expecting my heating system to work properly but I get fast hot air blowing from the defrost vents, marginal hot air from the center vents, decent hot air from the two vents by the sides of the dash and cooold air from somewhere under the dash. Also, when driving there feels to be cold air leaking in from around the gear shifter. I know the vent leading to the back seats is a fresh air vent but it blows cold air like no other even when the car is at a red light/stopped. I use the button on the climate control second from the left (next to the defrost button). Also, the AC compressor is not hooked up.

All pods seem to hold a good vacuum - checked with my mity vac. Climate control bad?

Any suggestions would be greatly appreciated!

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As far as I know, there shouldn't be hot air coming out of the two center vents. I think they are for the AC only.

It sounds like you may have some linkage issues with the pods if they all hold vacuum. Sorry I can't be of more help.

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

I've tried to get my flaps/pods working the first winter I owned the SD. I gave up and just rig the system to get heat. I unplug the monovalve (best heat), wedge the footwell flap so it is always open, and depress BOTH the defrost and one arrow button at the same time (I don't get heat out of anything but defrost mode). It works for me.

The rear vent will NEVER send any heated air. Only FRESH or AC air. I also have a bit of a draft coming through by the shifter. Only a small bit of rubber seperates the inside from the transmission area underneath.

I would suggest examining as many pods as you can to make sure all the linkages are hooked up correctly.


If you find anything, let me know because I wouldn't mind getting it operational in the original way. I'm replacing my dash (with an uncracked one from the jy) sometime so I plan on looking more into the situation at that time.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

The SD also has fully functional vacuum pods and it behaves in similar manner.

Firstly, the center vents should be fully closed when the climate control is calling for heat. If they are not closed, the CCU is signaling the thermostatic switch to send vacuum to the center vent pod and open it. This should not occur in the heating mode.

On the SD, I chose to provide vacuum to the center vents all the time and control the center vents via the dash sliders. As a curiosity, the temperature of the air exiting the center vents is not warm............apparently the source of this air is somewhere upstream of the heater core.

You'll need to be more definitive in the cold air from underneath the dash. The footwells should be offering hot air, however a bellcrank goes bad in the console and the footwells may not function because of it.

The cold air from the rear seat outlet is normal. Keep the slider in the closed position. Nothing you can do about it.

The cold air from the gear shifter is caused by a torn rubber boot that seals the shifter from the underside of the vehicle. The shifter has to come out to replace this boot.