Pulled the blower fan out on my 79 300SD to replace with one from a donor car. Got to looking at the fresh/recirculate flaps to see if I could tell how it worked by selecting the different ACC controls.

When the compressor switch is ON the recirculate door would close up but not all the way. The factory manual says 80% recirculate and 20% fresh air. The smaller pink pod (just to the right of the larger recirculate pod) would hold the door open slightly.

Solution: unplug the vacuum line from the pink pod and plug the line with something. Now 100% recirculate ONLY with the compressor switch is on. Which is what I wanted!


Hope this helps anyone looking to do this on their 116 car.

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1980 300SD Manganese Brown Metallic Clearcoat 248k
1979 300SD White 148 k
1984 300D Silver project car for daughter
1982 300D wrecked
1980 300SD 310K not running

I know this is old, but did this make any difference?
Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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If you drive long distances, running 100% recirculate is NOT a good idea. With no fresh air at all entering the cabin for extended periods, you run the risk of carbon monoxide poisoining or other trouble.

If you insist on doing this, open a window 1/4" or something for safety's sake.

Good luck,

I pulled my blower motor to replace the brushes and noticed a square slot cut in the air flap. Even when it's completely closed some outside air will sneak in. A nice piece of gaffer's tape plugged the slot up nicely. I am sure that this is true of 84 300Ds and 85 300Ds and CDs. Haven't looked at others yet.

I can't tell that it made any difference at all and I keep a thermometer in my air vent at all times.

I also found that keeping a window slightly cracked open will improve your air flow volume at the vents like it does in Porsches and VW Beetles. My seals are tight enough to pop your ears if you don't have a window open a bit.