erratic blower on 5000TQ

[Kelly Cole]

I have an 87 5000 CS TQ with a fresh air blower that has begun to work
erratically (runs at varying speeds, from 0 to high, frequently simply not
running).  Blower motor is new just last year and sounds fine when it is
running.  Hi speed control on A/C control head unit won't activate the
blower.  Diagnostic readout on channel 10 shows the value 45 with the head
unit set to 'auto' with the climate control temp set at 75 F.  I haven't
gotten around to testing the blower controller, so I'm just curious before
I start my step-by-step diagnosis what other people's experience
is  regarding the most likely failure (A/C head unit in the dash, veresus
blower controller by the evaporator, or something else).  I've had this car
since 88, and have replaced the programmer and blower fan, but the rest of
the climate control system is original (still blows cold air on its factory
freon charge!!).  Thanks in advance.

Kelly