I'm troubleshooting some problems with my heater blower motor. I removed the motor and turned it on via the defrost switch. No movement... gave it a spin with my fingers and it started to rotate. It continued to spin then clicked off then clicked back on... repeating this several times before I shut it off.

I also heard 'clicking' noises when I was trying to run the heater with the motor installed (no fan movement). The fuse was never blown.

It seems like there is some sort of overload protection build in... car is an '85 300DT. Anyone have any details on this? BTW, I don't think this is the source of my problem... I'll be searching for brush replacement / bearing renewal today (it wasn't obvious to me how to get to the brushes). If there is no 'overload protection' I may suspect the control unit...

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon

AFAIK, there is no protection for the blower motor. I have been told (by some folks who rebuild control units) that high current due to dragging blower motors is a cause of burnt out control units. I replaced both my control unit and blow motor at the same time to avoid damaging the "new" control unit.