300E-heat always on!
 

A friend is having trouble with his 1989 300E. The heat seems to come on for no reason (out of defrosters and side vents) regardless of which (or any for that matter) buttons are pushed on the control panel or what the temp. wheel is set at. The air coming out is very hot. The AC will work and eventually over come the heat but often the only way he can stop the heat is to shut the car down. It happens every 2nd or 3rd time he is in the car.

Have also had this problem, suspect duo-valves.

Duo-valves?
 

I think monovalve is more appropiate...:confused:

AS FAR AS I'M AWARE, ONLY CLIMATE CONTROL MODELS HAD A MONOVALVE

The 300E was sold only with the ACC in the US, no manual control models.

If the air only comes out the defrost and side vents, check the fuse -- default operation with no power is full heat on defrost with low speed or no blower. This happened on my brother's 300SDL in the winter, it wasn't until he was taking me somewhere and my feet got cold that we figured it out.

The fuse is probably corroded and loosing contact -- don't remember which one it is, but by now you need to check all of them.

Peter