blower motor problem 300E
 

I have an 89 300E that the blower is misbehaving in. Have not really had time to deal with it before but now it has become a priority as the temperature has dropped and the defroster needs to work!

Basically the blower doesn't come on for some time after the car is started and then will come on low and then kick up to high and then shut off again. It will keep doing this cycle for the duration you drive the car. In the warmer weather it blew cold air so I believe the A/C is still working and now it blows hot air when the fan kicks in. When the fan is off there is a trickle of warm air from the vents so I know the system is trying to let warm air through. It behaves the same on high or auto setting, not sure about low.

I'm thinking that the ground to the fan may be bad, the push button control is bad or its connections need to be cleaned.

Any thoughts? comments? Thanks, Andrew

Sounds more to me like the interior sensor has gone bad and the blower is being shut down because the control unit thinks it's getting too warm.

Is there anyway to bypass this sensor?

Next time it happens, try turning the ignition key just a touch to the left (towards off), with the fan set to high. See if the fan doesn't kick on. Those ignition switches are a known problem.

Another known problem is the pushbutton solder connection in the Climate Control Unit (CCU).
Try taking the CCU out, and resoldering the connections.
Do a search for the procedure, this has been a succesfull approach to many forum members.