Hello out there!
I have a 1990 420 SEL (194k miles) and when I turn on the AC, no matter which switch I select, the air blows out the defroster vent on the windshield and then after about ten minutes it starts to blow out the normal front vents. This goes back and forth switching every half an hour or so...? Any thoughts?

Normally on these cars they blow out of the defroster only because of a very common problem on them. Should have been a recall.

I think mine kinda blows out of the dash/defroster vents. My old W126 (1985) was defroster only.

Any idea what the problem is?

Probably a leaky vacuum pod under the dash, near the center console. It could be the vacuum control unit for the climate control, but the vacuum pod is more likely. Still haven't done mine yet....... Not looking forward to tearing the dash apart, either.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

Hey Tinypanzer,
Cool name! Thanks for responding. How far into the dash is the vacuum pod? Is it real involved to replace?

Yep, vacuum pods with busted diaphragms, no doubt. Of all of the vacuum pods on the climate system (I think there are 6 of them), the defrost pods are the only ones that are in the open position by default, so that if they fail (as yours apparently have), you still get defrost airflow. Neat engineering, plus, you're finding that it's a sure-fire indicator of a failed defrost pod. As for replacing them, I've never done it, but there are folks who claim the defrosts can be replaced by only removing the glove box and reaching way up to the left to get at the little buggers. When I asked my indy about it, he claims that they require removal of the dashboard, and a bill for 8 hours of labor. How adventurous are you?

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

One a 124 the dash needs to be removed to get to the top vacuum element. Photo is of 124 evap box item circled is what you would be looking at for a 124. Your model is probably similiar.

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