So I have been having this strange problem with the blower motor on my 1987 420SEL. Specifically the blower motor would slow down to a crawl at random times even if the switch was on high. So I initially thought it was the blower motor, but at last it was not, so I tried another blower control module (aka porcupine) which had same problem. So at this point I figured it was the Heater/AC push button unit, yes I checked fuses. Well I replaced the capacitors and resoldered the board. I still had same problem.
So after much investigation I found that the power to the blower porcupine had some AC voltage on it. I thought this was unusual and check diodes in alternator and found no problems. I also checked ground connections and everything looked good. So I found that if I placed a large capacitor across the input power to the porcupine that my problems went away. I was wondering if a capacitor inside the porcupine was bad, but I would not have expected two units to have same failure mode. Has anyone ran into this problem and if so how did you fix the problem? Thanks Trampas
