On Thursday, February 6, 2014 4:29:23 PM UTC-5, wrote:
Unlike the older models when the transistor heated up it transmitted the heat to its pins ,now the heat transmits to the whole pcb thanks to genius who decided to glue the pcb to the copper

I just discovered something important that I haven't seen mentioned
here or in any other threads on the BMW blower motor resistor (aka final
stage unit) problems. This module is mounted in a location where the
heat sink fins are directly in the blower motor airstream. It relies on
the blower air to keep it cool. From where it's located and how you
remove/install it, it's not obvious that the heat sink fins wind up in
the blower air, because you can't see where they actually are.

When I replaced it, to make sure it worked before putting it together,
I just left it hanging for testing. It overheats as soon as you slow
the blower to about 80% of full speed and stops working. Once I stumbled
on the fact that if it's mounted it gets air flow to cool it and
I mounted it, it's apparently working. Just thought I'd pass that along,
as it seems like something that could trip up a lot of people.