Can I run the blower motor without a regulator? - PeachParts Mercedes-Benz Forum

Zacharias · #1 11-16-2014, 07:25 PM

Is it possible to bypass the regulator/resistor and just run 12v to the blower motor?

This would assume using a potentiometer to allow some control of it.

leathermang · #2 11-16-2014, 07:38 PM

A potentiometer is just a variable resistor....
so I suspect if the one you use is of the proper size that would be fine..
but some EE person can chime in and give a more secure answer...

jay_bob · #3 11-16-2014, 08:00 PM

If you just connect 12 V to the blower you will get maximum speed and no control.

You can put a rheostat but remember that you will dissipate a lot of heat doing this.

Not very easy to do.

What is wrong with your controls that is making you want to do this?

Which car, 80 300TD with the ACCII (evil servo) or 85 300D with the ACCIII?

Zacharias · #4 11-16-2014, 09:23 PM

Quote:

Originally Posted by jay_bob

Which car, 80 300TD with the ACCII (evil servo) or 85 300D with the ACCIII?

Some time back I messed up while troubleshooting the ACC II on the '80. I connected up a spare blower motor to test it and managed to catch something in it and stopped it dead while on high. There was no 12v to the motor afterwards.

At the time I was told I had most likely fried the regulator/resistor in whole or part. Sure enough when I looked at it, there were some wires burned.

The 1980 uses a regulator similar to the 240d, completely different from the "toaster" on the later system -- and in a hard place to work with, under the front cowl by the wiper motor. Took me a while to find one used ($475 new), then I was occupied on the other car with several things so time slipped by.

I have now installed it and the system is still dead. No blower. We are into cold weather here now.

I would like to have the TD as a backup car for the winter. I want to remove the servo and just install a manual water valve to control the heat, but I still need some form of working blower.

A friend has a complete 240d system in boxes. He offered it to me months ago when this started and I wish I had grabbed it and just done the switch then. I plan to do so in the spring. For now I just need something that generates heat and blows air, mostly for defrost.

There is a video on YT of some scandanavian lunatic who installed a woodstove in his Volvo 240. Right now that is looking less insane by the minute....

Wodnek · #5 11-16-2014, 09:49 PM

I would not try to make a speed control for it. No easy way to get rid of the heat, and you could fry something. A simple on an off, can get you through spring.

Graham · #6 11-16-2014, 09:52 PM

Have you checked to see if you have power to the "new" regulator? Just thinking that something else may have fried further back in circuit. Perhaps at the fuse.

bricktron · #7 11-16-2014, 10:22 PM

yes, the original is spec'd to dissipate a good deal of heat, which makes it hard to reengineer.

if you had to replace it with something aftermarket, use a PWM (pulse width modulation) controller, which will probably have MOSFET power transistors. that would give you gradual control without emitting a lot of heat.

Zacharias · #8 11-16-2014, 11:37 PM

Quote:

Originally Posted by bricktron

if you had to replace it with something aftermarket, use a PWM (pulse width modulation) controller, which will probably have MOSFET power transistors. that would give you gradual control without emitting a lot of heat.

Something like this?
Amazon.com: Docooler 12V-40V 10A Pulse Width Modulation PWM DC Motor Speed Control Switch 13KHz: Electronics

or this?

RioRand RRCCM2SPC Adjustable DC Motor Speed PWM Controller 10V 12V 24V 30V Reversing Switch 120W - - Amazon.com

Zacharias · #9 11-16-2014, 11:42 PM

Quote:

Originally Posted by Graham

Have you checked to see if you have power to the "new" regulator? Just thinking that something else may have fried further back in circuit. Perhaps at the fuse.

Entirely possible that I fried something else. The fuses and the blower relay have been checked.

I guess the overall picture is that I am working outside and I have officially had enough of this system. For now, at least.

I would rather bypass and live with a cobbled together deal for the next few months, than pull the dash off, which is what further troubleshooting will require.