The fan motor in my 83 240D runs at low speed only. The climate control is manual and no matter which setting on the switch is used, it only runs at the low speed. I've deduced this down to the resistor pack, but this part is NLA and instead of being located on the passenger fender well, it's located inside the evaporator box.

I'm reaching out looking for an alternative. One which I found is using a DC motor controller. They are inexpensive and available, but what characteristics (meaning voltage) should I be looking for ? Top voltage should be 12vdc, but what is the range. Current I know should be less than 15 amps, but there so many options such a brushless, PMW, etc...

I'm sure there are other owners of these cars who have faced the same problem. Is this another viable alternative or is the anything else?

Greg

The blower resistors give you low and medium speeds. High speed should bypass the resistor pack to put full power on the blower. Check to see why you don't have high speed, it may not be your resistor pack.

Brushless DC motors are actually 3 phase AC motors that are driven by an inverter that makes AC from DC. Unless you change the blower motor, you can't use this.

PWM is Pulse Width Modulation. This is where the DC power is rapidly turned on and off to reduce motor speed, this works pretty well.

Resistor packs need cooling air and must be located in the HVAC air stream.

Do more diagnosis, use a incandescent test light / headlight to load the circuit so you are not picking up stray voltage. ( A digital meter can pickup stray voltage making it appear that you have power that goes away when a real load is applied. )

Thanks. I will attach a voltmeter to the blower motor connector and take readings at different switch settings and post findings.

I have something similar to this one 9-50V 40A DC Motor Speed Control Module PWM HHO RC Controller 12V 24V 48V 2000W | eBay in my 85, not because of anything wrong with the resistor pack, but because of noise. With the fixed speeds, middle is too loud, low is ok noise wise but not enough air flow. With the PWM, I can dial in exactly what I need in loudness/ airflow balance.

The one I linked to ships from China so it may be a long wait. If you want one faster, you can get one shipped from the US but you'll pay 3x more for the same thing.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Ok, voltage reading are not what was expected. Readings from 1st, 2nd & 3rd switch positions equal 12.32 VDC.
Checking the fan today, it appears that it does run at faster rpm's at the above listed switch settings. The other day in 20 degree weather the fan wasn't working but today at 55 degrees it's working correctly.

In getting the voltage readings I observed initially changing the selector switch from the 2nd position to the 3rd, the fan speed did not increase. Moving the switch back to the 2nd position and quickly moving to 3rd resulted in fan running at top speed. Now this brings up a few possibilities between the selector switch, the resistor pack and the fan motor. The first can be ironed out as the selector switch was replaced 3 years ago. It appears the resistor pack is working so the final part is the fan motor. Could this be a brush issue and what are the characteristics of failing brushes ?

It was probably on funola's recommendation (someone here recommended it...), but I have something almost identical in my 1983 240D. When I got the car on the road in fall, 2015, the 3-speed switch was wonky at best, and then it only ran on low speed.

First, I swapped my squeaky old blower motor with one from a Volvo 850, thinking that would also make it run on all speeds. The new one ran more quietly, but not at all speeds.

Then, I tried looking for a new resistor. They're NLA, and used ones (of unknown condition) are hard to find and expensive. Plus, I don't even know if it's possible to access the resistor with the dash in place. I can't find a diagram of it or instructions.

Then I considered installing a 3-speed resistor from another car - just slicing a hole in my airbox to mount it and then wiring it in. But, I didn't want to damage anything else by slicing the airbox.

So, anyhow, I installed one of these and I enjoy the infinitely-variable fan speed. Here's a video I did:

https://www.youtube.com/watch?v=j-oULis8cyI

MajicBus, your video was the inspiration for this entire project with using a DC controller motor, which I watched a few day's ago.
Have a few questions. In your video comment section, you state that you changed and upgraded the controller unit being used because of the whine, but it didn't state specifics. You've just mentioned in this thread that you used a 3-speed resistor from another car, but what car. Also, I agree with the concept of mounting it in the airbox, but where to cut the hole. Also, where did you mount the dial so as not to make it look obtrusive. I agree that the factory switch settings are not the best and I'd want to duplicate what you've done for it sounds fantastic.

Funola, I ordered your linked ebay controller today. Also ordered a set of brushes for the motor, for I suspect them as going bad. The ambient temp was around 32 degrees last night. When turning on the fan, as usual it ran at slow speed through all 3 switch settings. Upon tapping on the bottom of the motor, the speed increased. Go figure.....

Yes it was me who recommended it. How is it running? Where did you mount the control pot? An ideal place seems to be the OE rotary switch.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

When the motor is running at slow speed, feed power directly to the motor making good solid connections. If it still runs at slow speed, then it's the motor/ brushes. If it runs full speed, then the connector contact(s) may be loose.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks for the comment Funola. I like the idea of the OE rotary switch location. Only one question. The original OE switch serves two functions. One it controls the air flap door via a cable and 2nd it allows to the fan speed selection. Removing and replacing the switch should not be a problem with building a mount for the dial, but any suggestion about the vent flap ?

As mentioned, I've ordered new brushes for the fan motor and will have them next week. The DC controller I ordered from China so it will be a few weeks before that one shows up.

I do not have a 240D anymore and do not know what the OE mechanism looks like. You'll have to take it apart and see if it is easy, difficult, or too much trouble.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Actually, there were two issues. The noise from the first unit was a bit troublesome, but the unit was flimsy and I managed to damage it during installation. The speed controm knob stopped working almost immediately.

I replaced it with this, and have been very happy:
https://www.amazon.com/gp/product/B00JEXJXAC/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

The 3-speed resistor I bought was from a Porsche, but I don't remember the year or model. It was an aftermarket part, and cost under $20. That's all I remember. Rather than cause further damage by attempting to install it, I went with the unit above.

The only issue with the beefier unit I bought was that the knob didn't have an "off" setting. I also ended up installing a toggle switch to turn power on and off. I mounted the toggle and the knob from this unit on my upper switch panel, approximately where the rotary knob was. No photo, unfortunately.


Works like a charm. I'm very happy with this as a solution, despite the non-stock appearance.