Heater blower troubles

[Matt Daniels <mdaniels@a4.org>]

About two months ago the heater fan in my '93 90S stopped working with
the exception of the highest speed. After asking the list, I found out
that the heater resistor pack was the most likely problem. I ordered the
part from Clair, got it installed and everything worked fine - until
yesterday. The heater has again died with the exception of the top
setting. I'm sure if I replaced the resistor pack again it would solve
the problem, but I'm worried that there is some other problem which is
resulting in the resistor packs going bad. Any suggestions on what the
problem could be?

Matt Daniels
'93 90S
'86 4kcsq