164 stepper motor failure (electrical vs. mechanical)

[chris.robyn@xxxxxxxx (Chris Robyn)]

I've now had my 164/8 for over a year, and have since day one wondered if
the stepper motor was out of whack.  I've been reading the technical notes
on the 164 page about electrical and mechanical failure modes, and was
wondering if anyone out there has the same symptoms as my car.  Maybe it's
not the stepper motor after all.  The car is a '91 164 L (cosmetically
converted to a 168).

Firstly, the AC has given me no problems both in manual and "auto" mode as
it has consistently operated through the temperature range from "LO", which
is ice cold, and at all fan speeds with no problems whatsover.  The problem
occurs anytime I exit the "econ" setting and the compressor is engaged.
This can be done both by pressing auto or by switching off econ.  At this
point, the car begins an electronic whine like a bad stereo installation or
wires to close to the Bosch box (I have yet to poke around down there, but
will soon).  The whine only occurs only when the compressor is engaged and
pitch and intensity varies with throttle position, not the fan speed, which
makes me wonder if it is in fact the stepper motor after all.  In other
words, whether you leave the fan at #1 or #4, the pitch of the hum is the
same.  There seems to be no problem with the mechanical operation of the
fan speeds or temperature settings.  When you drive away at low rpms, the
whine alters pitch as the transmission shifts and the throttle is
depressed.  The net effect to the passerby is that the car takes on the
appearence of an "electric" 164.  At freeway speeds the noise is not
noticeable.

My question is do these symptoms point to an electronic failure of the
stepper motor or could this be something else, such as misrouted wires or
something much less severe?  I have reason to believe the factory GM stereo
may have been removed and replaced, as none of the buttons are illuminated,
though the LED display still works.  The car was at one time wired for a
cell phone, so that may be it also.  Before I commit it to the stereo shop,
however, I just wanted to see if this all seems plausible and if anyone
else out there has been through the same or similar thing.

Thanks.

Chris Robyn
84 GTV-6
91 168

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