Re: Blower motor woes

[zm@mhcnet.att.com (Zafer Mehmood [209])]

Rich wrote:
> 
> 	Here is a new one.  My 1990 200T has decided that the 
> blower motor is going to be intermittent.  Does anyone have any 
> ideas?   I checked the climate control diags and the climate
> control is indeed indicating that the blower motor should be
> on, but it is not.  I really have not had a chance to check
> the manual but if there are any short cuts, let me know.
> 

Bill responded:
> It's one of two things:  The blower itself has worn brushes, or the electronic
> speed controller is bad.

	There is one other possibility - the control head itself (the box
with the buttons and LED displays) or a loose connection behind it.
I had the same symptoms in my '87 5000 TQ. Diagnostics weren't much
helpful. This is what I found. There is an output from the control
head to the blower speed controller that varies from 3 to 5 volts (Low
to High blower speed). In my car, this voltage was dropping below 3 volts
during the "intermittent phase" and the blower wouldn't work. I ruled
out the speed controller and blower motor by providing 5 volts to this
output pin. There is a 5 volt input to the control head that you can tap
off of. The Bentley manual shows the pinout info. I suggest you try this
to determine if the problem is in the control head or its connector
before going after the speed controller/blower assembly. The control head
is easily accessible by popping the plastic panel in front of it and
removing a couple of screws.


-----------------------------------------------------------------
Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ