The blower motor is new. It was working great. Until just the other day.

Symptoms:
When the ignition is cycled into position "three", the blower motor works perfectly. It varies speeds, and does everything that is expected of it. However, when you start the engine, the blower motor ceases to function. Completely dead.

What could it be? Suggestions?

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

Bump, anything?

I would like to add that there was a point that the blower motor was not engaging at all. Even in key position 3. Now it works in that position, but it doesn't work as soon as the engine is started.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

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.

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

Thank you, Steve. I'll try that. I'll report back to this thread when the cause is determined.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

It did, in fact, turn out to be the blower motor regulator. Tested both live wires, and they were within voltage specs (1 - 6 volts depending on fan speed) for the climate control connection, and battery charge voltage level for the power wire.

Even when the car was running, these wires checked out within specs. So,...Ripped out the wiper assembly, multiple cowls and firewall gaskets, lots of screws bits and trim pieces, and 5 torx for inner blower motor bracket. Replaced with a used unit. Tested it. Problem is resolved.

Thanks again.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

is it worth it to replace the blower regulator with an used unit?

Prior to my blower motor not working, i recall the speed no longer worked as well and it didnt seem to cool as much, maybe just due to the speed of the blower.

Today we had finally a sunny day so i ventured to replace my blower with a pulled one from a diff vehicle.. which is probably as old as mine but works. (and it does work but it squeeks a lot lol), anyways.. i also purchased an used regulator which has yet to arrive.

I figured I would replace the fan today to learn and see how the process is, and then just redo it later, now I am wondering if maybe i should just buy a new behr motor and stick with the used regulator that i should be getting soon.

Which reminds me, if blower was working, and speed selector was working, if the car was low in freon what would I experience? not so cold air, when set to cold?

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89 300E - 240k +

1984 300d Turbo
Buy A New Voltage Regulator $28.00 Kit From **************.com Regulator, Guide Book, Tie Wrap, Diy 2 Screws Rear Alternator, Also Buy The Fuse Kit $10.00 And They Have The Brush Kit For The Blower $28.00