I just bought a 1991 2.5 turbo mercedes so i can start burning biodesiel. It seems to be a great car despite it's 200k miles (it looks like new) - but the heater motor does not work. These Mercedes seem to be a very automated car - especially the heating system or climate control as the german engineers like to call it. Here's the symptoms:

1) the heater motor does not work under any conditions
2) the temperature control dial does not seem to have much effect on the small amount of air that comes out of the vents. It always seems to be warm even when the dial is turned to a low setting such as 60 degrees.

Would it be prudent to replace the heater fan motor (it I could find it) or should I be considering some problem with the control unit somewhere?

thanks in advance,

Dino

300D Turbo 2.5
Replace all fuses, if that fails:
The blower motor and/or regulator is 90% likely the cause.

1991 Mercedes Benz 300D Turbo 2.5
Part: Heater Motor


1991 Mercedes Benz 300D Turbo 2.5
Part: Blower Regulator

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It is in fact a 300D 2.5 turbo

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Location is a big help, we may know a local garage or member who can help.

Oops
I edited my first post = added much more data.
Hmmm
What was engine temperature???
The CC will not allow blower to come on if engine is below 30C...

I'll check that fuse located on the left wheel strut (from another thread). The engine temp is right where it should be. Do you have any idea where the heater motor is on this 91 300D 2.5 turbo?

thanks,

Dino

If I recall correctly:
Remove the bezel, mid engine false bulkhead and motor cover to access.
Labor is roughly one and a half or two hours for a mechanic.
This is from memory, and I am very tired, will try to check service information tomorrow.

You must remove the wiper motor and gearbox, then unclip the cover over the motor and unscrew. Not bad, and you need to lubricate the wiper gear box and slide joint on the wiper while you are in there, too -- prevents burning up the motor or damaging the gears from excess drag on the pin.

Most likely it's only the fuse in the little black box. It's an aluminum strip fuse, do not jumper it!

Check all the fuses in the fusebox, too -- if they are geting corroded (white instead of silver looking), replace them all. If you have no power to the ACC pushbutton unit, you will have no blower and only hot air out the defrost vent.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Fred,

I guess I'm into the heater motor now since the fuse is OK. The ACC pushbutton unit seems to have power since it does successfully redirect air flow between defrost and heat vents. Where do I remove the wiper motor. Is it reached from outside the car under the hood?

thanks,

Dino

This sounds like the behavior of the control unit when the auxilliary electric water pump locks up and shorts out. Mercedes uses a small electric pump to circulate hot water through the heater core. This ensures your toes stay toasty even when idling at traffic lights. The problem is, anytime after ten years or so, the pumps lockup and short out.

It's easy to test. Just unplug the pump and see if the operation changes. I'm not certain of the location on the 1991 diesel, but on the earlier 124 chassis diesel cars it was located directly underneath the windshield washer reservoir. The pump itself is a small black contraption with two rubber coolant hoses hooked up. Should be pretty obvious. There is a connector which can be unplugged, effectively taking the pump out of the system.

If all works well with the pump disconnected, you can leave it that way indefinately. If you want better/more heat, then replacement of the pump is required.

- JimY

Yup, it all comes out from under the hood.

I've not done this job yet, but I suspect I will soon -- squealing fan, sooner or later it's gonna stop.

I would do a search, I do believe this has been explained nicely by someone in the fairly recent past.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I'll try the small electric pump to circulate hot water through the heater core as mentioned by JimJ and the heater blower motor itself as mentioned by spfred. These MB's sure were not put together by a shade tree mechanic were they? Seems like a contest to see how many systems they could squeeze in there and keep us guessing.

Dino