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help, i have a 98 e-320 and the ac blows out of the defrost vents at times when it's suppose to blow out the front vents. tried cycling vents with control unit but nothing happens. at times it'll cycle fromfront vents to defrost vents and back on it's own.also the blowermotor seems to whistle especially at lower speeds. any suggestions?

 

I have a 92 300 TE wagon doing the same thing. Have you had any luck finding out what is causing it?

 

yes i found the problem to be a servo vacuum control block.it has a bunch of vacuum lines connected to it and it controls the ac duct valve via the dash ac control unit.it has a three wireelectrical connection.it's located behind the glove box and is accessed under the passenger hush panel.i don't know if your car has the same type setup.if it does you can disconnect the electrical connector when the ac blows out the front vents and it should not switch to the defrost vents.this will verify the cause.

 

Thanks I will give it a try.