124 HVAC Blower Motor Regulator - PeachParts Mercedes-Benz Forum

Maxbumpo · #1 02-19-2015, 09:54 PM

Did someone design a cheap solution to bypass the regulator and provide manual control of the blower fan?

'87 300TD, ~338k miles. I've got a bad blower motor regulator. The PBU is producing the correct control voltages, the fuse is good, and when I short to ground the blower motor connection with blue wire, the fan runs REALLY fast.

The fan motor is relatively new Bosch, which I installed a few years ago.

Another clue that it is the regulator: With the high speed fan button pushed in, the fan turns but there is a distinct whine from the fan/regulator area. When I apply 12v directly to the fan and it turns REALLY fast, no whine.

sixto · #2 02-20-2015, 02:11 AM

Wrecking yards are chock full of 124s with functional blower regulators. Yes, it's a PITA to replace and repeat if you find a dud but they usually outlive the car. If you really want manual control, take the knob and resistor pack from a 240D and have at it.

Sixto
MB-less

funola · #3 02-20-2015, 09:35 AM

Quote:

Originally Posted by Maxbumpo

Did someone design a cheap solution to bypass the regulator and provide manual control of the blower fan?
.................

What do you call cheap? I am working on a PWM blower motor controller that has a knob to continuously vary the speed from zero to max RPM. Would that be of interest?

Maxbumpo · #4 02-20-2015, 10:08 AM

Quote:

Originally Posted by funola

What do you call cheap? I am working on a PWM blower motor controller that has a knob to continuously vary the speed from zero to max RPM. Would that be of interest?

In this case, Cheap = $50 or less. Aftermarket regulator is over $200, I'm not even going to ask the Classic Center how much new from MB costs. I would imagine that $20 is about the cost for a used regulator at the local knackers.

Yes, I would be interested in your PWM modification.

Phillytwotank · #5 02-20-2015, 10:09 AM

Quote:

Originally Posted by funola

I am working on a PWM blower motor controller that has a knob to continuously vary the speed from zero to max RPM. Would that be of interest?

That'd be awesome.

Maxbumpo · #6 02-20-2015, 10:10 AM

Quote:

Originally Posted by sixto

Wrecking yards are chock full of 124s with functional blower regulators. Yes, it's a PITA to replace and repeat if you find a dud but they usually outlive the car. If you really want manual control, take the knob and resistor pack from a 240D and have at it.

Sixto
MB-less

Planning to head to the knackers tomorrow, intrigued with the idea of adapting the 240D manual controller... I wonder if it can support up to 28 amps?

vstech · #7 02-20-2015, 12:03 PM

II am dubious that a controller designed for a 16 amp motor can handle a 30 amp one...

tjts1 · #8 02-20-2015, 12:48 PM

Quote:

Originally Posted by Maxbumpo

Did someone design a cheap solution to bypass the regulator and provide manual control of the blower fan?

Yes
W124 Manual Blower Control DIY

jay_bob · #9 02-20-2015, 01:59 PM

That works assuming the regulator is good. He's just overriding the control signal from the PBU to the regulator with an external potentiometer.

I agree try the yard first. I found a blower/regulator assy out of a 91 gasser that I dropped into my 87 300TD since my blower was starting to make noise. Not a terribly difficult job, worst parts are getting the windshield trim pieces off without breaking anything (be careful and go slow), not dropping the nuts for the wiper motor into the great beyond (use a magnetic socket or tape), and not launching the spring clips holding the 2 halves of the blower case into the next county (tie on string or just be prepared to catch it).

I would as a follow on to this job, while you have it open, get a can of Scrubbing bubbles bathroom cleaner and clean the evaporator. Make sure the drains are intact first!

Maxbumpo · #10 02-20-2015, 04:57 PM

Last night it took me about an hour to get to the blower motor, and about an hour to put it all back together. Third time, getting faster...

Maxbumpo · #11 02-20-2015, 05:04 PM

Quote:

Originally Posted by tjts1

Yes
W124 Manual Blower Control DIY

Thanks! I was looking for that thread last night. Unfortunately, that mod won't work with a dead regulator.

Something to think about though...

funola · #12 02-20-2015, 05:08 PM

Here's bench testing my PWM controlled W123 blower motor. You can see the varying PWM oscilloscope pulses as the motor speed changes. I have to install it in the car to test when it gets warmer. PM me if interested. Probably won't be available till about 2 months from now.

https://www.youtube.com/watch?v=Q2zGIskBORs

dieselbenz1 · #13 02-20-2015, 09:29 PM

Quote:

Originally Posted by Maxbumpo

In this case, Cheap = $50 or less. Aftermarket regulator is over $200, I'm not even going to ask the Classic Center how much new from MB costs. I would imagine that $20 is about the cost for a used regulator at the local knackers.

Yes, I would be interested in your PWM modification.

About 5 years or so ago I put in a Chinese regulator that was $33 and it is still working great the prices at the time were all over the map from 33 to over 300.

sixto · #14 02-20-2015, 09:59 PM

When you fit a used replacement regulator, run wires from the motor outside the airbox. If and when the used regulator quits, unplug connector to the regulator by the brake booster and use the added wires with whatever device you choose to manually control the blower. You'll have enough work to do without tearing apart the cowl just to run a couple of wires.

Sixto
MB-less

HappyHappy · #15 02-20-2015, 10:32 PM

The semiconductor device under the black plastic can also be swapped between different shaped heat sinks used on 124 cars versus 126 cars, you just need to reapply some silicon heat sink paste in between the heat sink and the device. The controller in 126 cars is easier to get to under the passenger dash up and behind the fan enclosure cover.