There is a three wire connector on the firewall that contains the power the ground and the control signal to the blower. You are loosing one of them (or more). The control signal comes from the pushbutton controller and should vary from 1v to about 6v for high blow. If it is zero volts the blower will stop. The power must stay at near battery voltage.

See what leaves and proceed from there. If they are all OK the problem must be in the blower assembly or blower regulator. Its hard to imagine how the engine running could matter, but recently I had a car brought to me with the concept that I should install a trans controller.

Another shop had rebuilt the trans and the valve body was replaced because it didn't shift and now they wanted me to replace and code the trans controller.

As I was checking it out I found that sometimes it would shift. It had no codes. It was really messing with me and the fool drivers window wouldn't work and the seat wouldn't work and I'm 6'4". I was getting aggrevated when I noticed that the window was working. I though Ahhh an ignition switch problem as the car was off but the key on. So I started the car and the window stopped. I wiggled the key but the window would not work. I wiggled until the engine died, dang that window worked. Back and forth, back and forth engine off window worked, engine on window didn't work. What was the relationship???????

The only difference was the alternator!! That fool alternator was charging at 18volts, darn near every control unit in the car was shutting down to protect itself. Slammed a voltage regulator and the transmission started working the window stayed working and even the seat was working. So sometimes the wierdest things happen.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician