I have a 1990 560SEL with the HVAC blower motor not working. The climate control unit seems to be operating everything else because I can feel cold air through various vents at different button positions while driving down the highway, but no blower even when in defrost mode.

I dug into the dash this morning and got the motor running inconsistently after unplugging and replugging to test voltages. This system is different from what is shown in the shop manual (CD) in that there is a huge heat sink on top of a small electrical connector on the inside of the blower motor cover. Instead of two wires directly to the motor, there are three wires (red, black, white/blue) going to the heat sink, then two (red & blue) to the motor. Also, I couldn't find any preresistors under the hood. I am getting 14V between red and black before the heat sink, and a variable voltage between the white/blue and black wires depending on manual speed setting, so I don't think it is the CCU. Motor resistance is 0.4Ohm. I am getting 14VDC or 26VAC (tried both settings on multimeter) out of the heat sink device (I think blower regulator), which does not change with manual speed settings.

Is there a method of testing the blower regulator? That looks like a pretty pricey part

Is this climate control system better shown on the W124 shop manual CDs?



Thanks

__________________
Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)