Inside the box: Blower Resistor Relay box
 

GEBLASEREGLER 12V
1147 328 026
PART NUMBER 000 822 1103

FIRST GEN 126 - BLOWER MOTOR SPEED/RESISTOR CONTROL UNIT
REMOVED FROM 500SEL

• http://i.imgur.com/12hiJl.jpg
• http://i.imgur.com/Xzz0yl.jpg
• http://i.imgur.com/Fuspul.jpg
• http://i.imgur.com/aQou8l.jpg

Is that my new to me unit? :D

I am going to replace the ICs and caps. All the parts are crazy cheap from Mouser Electronics. Mouser.com :)

Now if that is not my problem, time for me to buy a new climate head I suppose :( Not having low speed sucks

I tested that out in the green SD, it had low speed. Performed same as the green SD's unit.

Hopefully its your problem.

:D I hope