1983 240D HVAC blower motor issues

[MagicBus]

Hello, all

As the title suggests, I'm having issues with my blower motor. It only works on the low speed and it was very squeaky/noisy going in to last winter. I don't drive the car after the snow flies until the roads are salt-free in the spring, and in the good weather, I just tend to drive with the windows down.

Knowing that there's at least SOME issue with the blower motor itself, I went to the junkyard this morning and pulled a blower motor out of a 1997 Volvo 850 (not a fun job). There aren't detailed instructions on this on the forums anymore. There is an old post, but the photo links no longer work.

Long story short, I was able to swap the Volvo blower motor into my car by using the original Mercedes plastic HVAC motor mount housing, the original electrical connector from my car, and the fan blade cage from my motor.

The new motor runs strong when jumpered directly off my battery, but runs only on low speed when installed in the car (I assume that the replacement motor solves at least the noise issue I was having).

So, what do I look at next? Is there a relay or resistor somewhere in the system? If so, where? Should I suspect the rotary switch itself?


Worst case scenario, I can run a new fused wire and switch directly from the battery to turn the fan on to high speed when I want to. But, if it's easy and cheap enough, I'd like to get it working correctly. Any advice would be appreciated.



Incidentally, I will be posting a video of swapping in the Volvo motor to my Youtube channel. I'll post a link here when it's ready.

[MagicBus]

As mentioned, here's the video on retrofitting the Volvo 850 blower motor into the 240D.

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

Works like a charm, by the way.


After reading, Googling, and thinking last night, I believe my low-speed problem is due to a bad resistor. Unfortunately, that part seems to be very expensive and hard to find.

So, either I'm going to try to come up with something on my own to mimic the factory part, or I'll run a separate fused switch to run the fan at high speed when I want to.

[funola]

Highly recommend you get one of these Max 10 50V 2000W 40A 12V 24V 48V DC Motor Speed Control PWM HHO RC Controller | eBay instead of wasting your time with the resistor. I just installed a similar unit bought last year and this one is better and cheaper, the pot is on wires (mine is not) which makes extending it easier. You can infinitely vary the fan speed. I like to set it to around 4 to 5 amps where it moves enough air and still is quiet. I find low fan speed on the stock setup too low and the other 2 speeds (auto and high) too high and noisy. This PWM control solves all that.

[MagicBus]

Now that... is interesting.


Maybe I'll go that route. But, today I placed an order for a 3-speed resistor pack meant for a Porsche that I should be able to make work for my application.

[Zacharias]

Originally Posted by funola

Highly recommend you get one of these Max 10 50V 2000W 40A 12V 24V 48V DC Motor Speed Control PWM HHO RC Controller | eBay instead of wasting your time with the resistor. I just installed a similar unit bought last year and this one is better and cheaper, the pot is on wires (mine is not) which makes extending it easier. You can infinitely vary the fan speed. I like to set it to around 4 to 5 amps where it moves enough air and still is quiet. I find low fan speed on the stock setup too low and the other 2 speeds (auto and high) too high and noisy. This PWM control solves all that.

Interesting. I find the blower speeds/noise issue to be a major irritant with that system.

The older ACC system is even worse, as it has no provision for any fan control apart from response to temperature settings.

[MagicBus]

Update - in addition to the Porsche resistor unit I bought, I took funola up on his suggestion and ordered a similar unit. I'll let you all know which I install and how it goes.

[Demothen]

Are you planning on wiring one of those in series with the resistor pack? If so, you need to actually get a full 12v signal to your new regulator or it's not really going to work well. You probably need to at least bypass the resistor pack. Have you tested the resistor or checked to see what voltages you are getting at the fan? I am not familiar with the late 240d, which generation climate control do you have?

[MagicBus]

Originally Posted by Demothen

Are you planning on wiring one of those in series with the resistor pack? If so, you need to actually get a full 12v signal to your new regulator or it's not really going to work well. You probably need to at least bypass the resistor pack.

In short, no. If I use the Porsche resistor, I'll wire it in the way the Mercedes resistor is wired. The more I think about it, the less likely I am to go this route.

If I use the DC motor controller I ordered, I'll disconnect the factory stuff and run new wires (fused appropriately) straight from the battery to the DC controller and from there to the blower unit. In that case, I'll most likely leave the old switch (not opening up my console again) and the old resistor in place.

In fact, I'm as-of-yet unable to determine whether or not I can even access the existing Mercedes resistor pack without completely disassembling the dashboard.

Originally Posted by Demothen

Have you tested the resistor or checked to see what voltages you are getting at the fan? I am not familiar with the late 240d, which generation climate control do you have?

I haven't tested anything yet, although I did jumper the new fan straight to a battery (it went on to full speed and ran quietly), so I know the fan itself isn't the issue. Plus, it works at low speed. That leaves the resistor and the switch as suspects. I'm leaning toward the resistor.

I ordered parts so that I can (hopefully) take a look at this over the long weekend. I wanted parts in hand so that I could fix this right away once I do a little more exploratory surgery.

[Demothen]

I would personally guess that your switch (or relay) is the problem, not the resistor, if you are only getting low speed. Without looking at a wiring diagram, i think typically the resistor is bypassed in full speed.
Anyway, good luck!

[funola]

Pic was taken with engine off, i.e. not charging. Right meter is volts, left meter amps. I have it wired with short jumpers in between the blower and blower connector for shortest path. I leave OE fan switch on high. If fan switch is on low, blower does not run with the controller. Not sure if that is bad for the controller or not when on low long term. Didn't do any harm in the short test on low. I'll probably leave the controller near its current location except mount it lower near the floor because it is cooler. If test goes well, I'll un-solder the pot, extend it with wires so it can be mounted somewhere I can reach.

[jay_bob]

The 240D manual control knob should be able to be mechanically adapted to use the speed pot. It would keep the stock look and be a nice upgrade.

The stock 240D fan control has 2 parts, a Bowden cable and electrical contacts.
Knob at 6:00, outside air flap totally shut, no power to fan
Between 6 and 9, flap opens, still no power to fan.
At 9, low speed fan (both resistors in circuit)
At 10:30, mid speed fan (one resistor bypassed)
At 12, high speed fan (both resistors bypassed)

If it was me I would delete the Bowden cable from the back of the fan switch and force the air flap open always.
Delete the electrical contacts (arrange the fan drive to always have power whenever the key is on).
Fit the speed pot to the back of the switch assembly. if you want to get fancy find a pot with the switch that actuates at the far CCW rotation, use that to drive a relay to the fan drive power to completely shut off the fan. If you go that route then you can use unswitched battery (circuit "30") on a new dedicated fuse to the contacts on the relay and set the relay coil up for switched power (circuit "15").

[MagicBus]

Originally Posted by jay_bob

The 240D manual control knob should be able to be mechanically adapted to use the speed pot. It would keep the stock look and be a nice upgrade.

In theory, yes, but that would require even more disassembly, and taking the console apart again. I have time to make this relatively neat and clean, but not time enough to make it quite that slick.

[MagicBus]

All parts arrived yesterday. I have the Porsche resistor pack in hand, as well as the DC motor controller, new wire, a fuse holder, and an on/off switch rated to handle the electrical load.

1. I'm still not 100% sure if I'll try to adapt the Porsche (aftermarket replacement) resistor pack or not. Knowing how this has to get adequae airflow so that it doesn't overheat and burn out - or worse yet - start a fire?? - I have little margin for error. There's also the matter of slicing an appropriately-located hole in my airbox to use this. On the other hand, it should get wired in place like the Mercedes factory regulator and allow use of the factory conrol knob.
2. As I said, I also have the DC motor controller, switch, wire, and fuse holder to add the new controller on aseparate circuit. I got a controller similar to the one (if not identical) posted by funola. The knob feels like it has a clear on/off position, which means that I may not need to install a separate on/orr toggle for this - making for a cleaner installation. I would likely need to extend the wires from the control box to the control knob - I'd want to mount the box near the HVAC airbox, and I would want the control knob on my upper switch panel in place of a dead switch.

Unfortunately, UPS arrived late in the day yesterday and I didn't have time to attempt an installation before the rain. Maybe later today. I'll keep you all posted on what I do.

[MagicBus]

So... I ordered the controller suggested by Funola, though I ordered from Amazon and not eBay. I tried to install it last night. I had a few issues (that I'll detail below) and will be returning it.

There were no instructions, but the board itself labeled the electrical connectors power +, power -, motor +, motor -. I ran a new fused wire straight from the battery to the controller and then from the controller directly to the fan motor. I verified the polarity of the fan motor wiring against the wiring diagrams. However, the board was labeled wrong and had reversed the polarity for motor output. The fan spun backward when connected up as labeled. I assume the power + and power - terminals were labeled correctly, as the controller powered on and worked.

Also, I liked Funola's idea of extending the cable to the knob. As it is, the knob's on a pair of cables that are maybe six inches long, which I find to be essentially useless. So, I tried extending the wires. That's when I realized how thin the wires really were. There was maybe a single strand of wire inside the housing. The pair of cables went to a two pin and a three pin connector, so I had to make ten connections. I simply couldn't get clean connections, and as a result, this didn't work for me. It's of poor somewhat poor quality, but OK for the money. If I were to buy this one again, I wouldn't try to mod the cable. But the wrong labeling is inexcusable.


I ordered what looks like a beefier unit. If I have to, I'll mount it right on the dashboard, but the new one coming has a knob that can either mount in the controller housing or mount remotely. The knob is on a 12" or so cable, so I should be able to remotely locate the controller housing.

I still like the idea of variable fan control.

[funola]

I thought the motor connections on mine was labeled backwards also, until I double checked. It was I who was mistaken.

I'd extend the wires by replacing the entire length and not splice into it. Yeah, Chinese electronics are really skimpy on copper. If the unit works fine otherwise it may be better keeping it.

Right now I "extended" the knob with a soft piece of rubber vacuum line from vacuum Tee's and a chopstick so I can reach without leaning way over not being able to see, which is dangerous when driving.