Mysterious 123 Heater

[mamali]

Hi the heater in my 300d works in a strange way. It works up to 30 MPH and blows hot air after 30 MPH it works as an AC?? Any thoughts? Thanks

[Motorhead]

Rebuild the MONO valve on the firewall. Should fix it. My wifes old '84 did the same thing.

[tangofox007]

Originally Posted by mamali

It works up to 30 MPH and blows hot air after 30 MPH it works as an AC??

That's a classic symptom of a torn monovalve diaphragm.

Obtain one of these:
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2650Q36L326Y0JME7T&year=1984&make=MB&model=300-DT-001&category=R&part=Mono+Valve+Repair+Kit

[mamali]

Thanks guys