[Peter Guenther]

I also posted on mercedes shop

The blower motor comes on for 1.5 seconds after each engine start if the engine exceeds 1200 rpm. It comes on if the temperature in the box is over 60C, and off at less than 55C for 6/8 cyl (5 degrees less on the v12). The air is drwn from under the dash and returned to the blower housing. it is controlled by module N16/1 in the box (the one with the fuses) it must get its power in there. I found the info in my 92 140 intro to service manual, and also believe it was deleted some years later. I cant prvide any more info than that.

 

[bayhas]

as mentioned above, its an over engineering peice because:

-Is was deleted in the later years...

-I ve only seen mine on once, on one of the hottest days i ve seen in my life... I mean for the box to be at 60 degree... the engine compartment ambient will be at what? 700?

 

[dbmoylan]

Thanks guys. I agree that this is set to go on at 60C which is about 140F I believe. Cute device, though I would have preferred it stayed on constantly, like a desktop computer, or that they have put the computers in the trunk or away from the engine's heat. Keeping silicone cool is a good thing w/ the internal heat they generate, esp. considering the price & consequences of a computer board failure to our cars.

Would you happen to know if the heat sensor can be seen from the outside - want to heat it up to test to see if it will send power to the blower motor to go on. Have already tested the engine startup at 1200 rpm and goes on, as well as tested the motor.

Thank you.

 

[bayhas]

Thanks guys. I agree that this is set to go on at 60C which is about 140F I believe. Cute device, though I would have preferred it stayed on constantly, like a desktop computer, or that they have put the computers in the trunk or away from the engine's heat. Keeping silicone cool is a good thing w/ the internal heat they generate, esp. considering the price & consequences of a computer board failure to our cars.

Would you happen to know if the heat sensor can be seen from the outside - want to heat it up to test to see if it will send power to the blower motor to go on. Have already tested the engine startup at 1200 rpm and goes on, as well as tested the motor.

Thank you.

You know how W140 is overengineered for no reasons in some areas? you are now over testing for no reason...

 

[dbmoylan]

I'm inclined to agree with you Bayas - given that I understand that later model W140s removed this blower motor I understand. Wonder how they cool the computer modules if at all? Still think factory should have placed the computer modules in the trunk away from any heat source. Oh well . . .

 

[bobs]

My '97 model has a small tube going from the electronics box to the HVAC blower housing. It looks to me like the new design just uses the vacuum from the HVAC blower to draw fresh air through the box.