has anyone experienced vapour mist coming from the windshield defrost vents when turning on the climate control.it comes out for a few seconds fogs the lower section of the windscreen and then clears very quickly.happens rarely but is it anything to worry about? 1990 300te 4matic

Not normal, but not rare, either. Mine has done that for a couple years. I think there is a check valve leaking down. I haven't bothered to try to fix it since it's working OK otherwise.

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Steve
'93 400E

Just so long as it does not smell like antifreeze, don't worry about it. It's just water vapor condensing on the cool windshield. If you've been running the a/c before shutting the car off, there's lots of water in the drain pan of the climate control system. Some of this evaporates, and then condenses when it is blown onto the windshield when you start the car. No big deal.

The vapor on the windshield when a/c is on is because the actuators in the system have a leak. Most times this also keeps the fresh air doors from closing properly which will allow outside air into the a/c system and make it not cool properly. You will have to go to the switchover valve group and check all the vacuum lines with your mityvac and see which ones are leaking. If the fresh air actuators are leaking then dash removal is required. There is aso one in the case that the heater core has to be removed to replace.

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euro 287
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck

On my 87, pccasional vapor on the windshield must be an expected event. The owners manual says the center AC push button (2 white arrows) is only to be used when the windshield starts to fog, and the system should be switched back to normal once the fog/vapor is cleared up. But I have only needed to use it a couple of times.

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John

2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)

Click to see 87 300E

If you have the a/c on and the button pushed solid white arrow down that is center vent only you should not get any air out of defrost if you do than you have a malfuntion in the servo system.

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euro 287
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck