The blower motor on my 300D works when 12 volts are applied directly to the motor. I've replaced the push button controller and 2 relays behind the glove box with workable replaced units and the fuse is good in the fuse box under the hood, but the blower will not activate. What else should be checked.

I have an 85 300D, and at times my blower will just not come on. It is all controlled through the monovalve that sits at the back of the engine near the fire wall. I have found that just removing the small electrical connection at the top of the monovalve, and cleaning those two pins that go into the connector will solve the problem. It seems very sensitive to getting the required voltage.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Which 300D? If a 124, it is controlled by the "porcupine" variable speed controller beneath it. I have a spare, PM me if you need one.

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Gone to the dark side

- Jeff

Actually, both the monovalve and blower are controlled from the climate control unit. It sounds like you have discovered a strange interaction between them. My old CCU seemed to cause all types of magic before I replaced it.

When my blower stopped I removed the blower and connected 12 volts to it from a battery charger, the blower ran on high speed with no problem in the downward position. When I re-installed the blower in the upright position and turned the blower switch on the blower failed to start. The brushes were worn down where it started to eat the armature on the motor shaft and only worked in the upward position. My first mistake was not checking for 12 volts at the blower motor plug. I went down to my mercedes parts store and bought a new blower motor replacement for $116 and took about 5 minutes to install it. Thanks to all for your help and I really appreciate people willing to send me parts at no cost. Just proves old mercedes people are the best.