Help! Advanced Wiper & Blower Motor W124 problems
 

My MB 91' 300E electrical system is conspiring against me!

A few months ago, my blower motor started to get intermittent...slow on...then didn't come on till car restarted...then finally died.

Following advice on this forum, I inspected fuses (good) & motor (hot wired as good - but still replaced the brushings) and by deduction, again on advice of this forum, I replaced my blower regulator unit (so called porcupine resistor) with a used one that tested good. And joy was had ... for about two weeks.

The blower motor again started to get intermittent...slow on...then didn't come on till car restarted...then finally died. Again. So I left it dead, but now am getting up the nerve to tackle again.

To make matters worse, last night the wiper got slow (heavy snow) and eventually fried motor fried - stinky! So this one is a two-fer. I am concerned however that the burn out of two regulators and a wiper motor in the span could be a symptom of a bigger problem.

Any pros wish to weigh in? Is this all coincidence, or could all these be related? (Especially, the two blown blower moter resistors together?)

Can you suggest a test to diagnose, or is this just a matter of puttng in more parts and crossing fingers?

It was suggeted to me that the resistor could have blown if the blower motor was drawing too much current... how do I test? Is this fixable?

-J

A check of the charging voltage might reveal a problem. Every so often you'll find a voltage regulator that fails and overcharges to 16-17v. When that happens it's usually found when looking for the cause of other electrical maladies. Starting to sound familiar? Given that 124 blower regulators are a rare failure it is plausible that it's demise is a symptom rather than the root problem. You shouldn't be charging more than 14.7v max but 13.5v is average. Make sure you're within that window.

Car does not use resistor control on blower . It uses transistor voltage regulator. This will fail if blower motor is drawing too much current [bad brushes/beraings]
Ground Blu wire at regulator while taking Amp draw test of blower . This will be max load and should not exceed 25Amps.