124 electric fan - PeachParts Mercedes-Benz Forum

duxthe1 · #1 12-21-2015, 10:58 PM

Cleaning up my workshop over the weekend I realized I had most of the parts to tackle a project I've been mulling in the back of my head. I've been wanting to ditch the viscous fan clutch in my 124 coupe in favor of an electric fan. Cleaning up the workshop uncovered a 203 fan assembly that was replaced after some front end damage. The frame was busted but the fan and motor are in good shape. From another corner appeared a 124 fan shroud and radiator.

A few minutes later armed with only a T20 torx the 203 fan blade comes off, along with the fan motor and controller. You can also see the 124 shroud in this pic for comparison.

duxthe1 · #2 12-21-2015, 11:03 PM

In the next pic you can see the 203 fan blade in the 124 shroud. It's a pretty close fit. With the rear portion of the two piece shroud assembled the fan blade may be too close without trimming. I'm going to try to use both pieces of the shroud but won't be too upset if I end up with just the one.

duxthe1 · #3 12-21-2015, 11:14 PM

The tight fit of the blade in the locking ring of the two piece shroud allowed me to center the motor and begin building a frame. I'm using 1/2" square aluminum bar I had lying around. I'm sad to cut it up its been a handy fing-longer more than once.

The motor has three mounting lugs that protrude about 8mm. I've got my frame drilled to accept these lugs and use the original mounting screws, though I could stand to find some longer ones. I plan to add reinforcement patches where it mounts to the shroud and use machine screws to mount it.

I'm hopeful that once the frame is mounted at the correct depth the fan blade will be far enough forward that I can trim the shroud and keep both pieces for no other reason than a more finished look.

duxthe1 · #4 12-21-2015, 11:24 PM

So this is where I'm at right now. I plan to weld the joints in the frame. I need to get my argon tank filled first.

For control I plan to use the PCS transmission controller that is already in the car running a 722.6 transmission. It currently has 3 unused PWM outputs. It can easily be configured to output a PWM signal based on engine temperature. The 203 fan controller uses a lower voltage input but a simple voltage divider circuit should get the PCS 12V PWM signal into acceptable range.

I still need to pillage a late model MB in the junkyard for the harness and connector. It's a pretty heavy gauge wire and instead of making my own harness I'm inclined to use the OE part.

I'll post progress as it happens.

whipplem104 · #5 12-22-2015, 10:32 AM

Have you scoped a w203 signal to see what the wave form looks like? Also get the frequency besides the voltage. I run an older one in my car from the old c classes and slks etc. The square box. I use a standard 12vlt pattern on those no problem at I think a pretty low frequency.

duxthe1 · #6 12-22-2015, 03:09 PM

Not yet but it's on the to do list. On the 203 I know it needs a signal to hold it off and as the signal decreases fan speed comes up.

duxthe1 · #7 12-23-2015, 08:51 PM

I had an opportunity to scope the signal line on a 203 fan today. It is a PWM signal, 10Hz, ~3.5V.

It isn't exactly like I was thinking but doable none the less. 10% PWM equals fan off and the activation allows you to step up 10% PWM at a time up to 90% PWM. The car I tested today had about a 3.6 to 3.7 volt signal and the service literature says over 3V is a good signal so it should be pretty easy to output a PWM with the PCM and use a voltage divider to get it around 3.5 volts.

whipplem104 · #8 12-23-2015, 09:59 PM

It really had a 3.5vlt pattern or was this the average voltage with a vlt meter?

duxthe1 · #9 12-24-2015, 01:10 AM

Yep 3.5 volt sharp square wave.

vannatta20 · #10 12-24-2015, 11:15 PM

I tired to install a electric fan in my W124 today and failed. There is not much room with that inline 6! I grabbed a Volvo unit and gave it a try.

duxthe1 · #11 02-28-2016, 12:20 AM

I spent some time this evening working on the fan. I've now got the fan motor mounted, the controller mounted and the fan blade clearing the housing. I sourced a harness from a 211 and have now run the fan off of a power supply.

Here's a couple pics of it mounted on a spare 124 radiator and a shot of the back with the controller mounted.

duxthe1 · #12 06-28-2016, 09:55 PM

I've been frustrated enough lately with the Coupe running hot to get back at the electric fan project. I finally connected my TCU to the engine temp sensor this past weekend. I used that input to skew my line pressure table because engine power falls off quite noticeably with a hot engine and even more so when on the verge of overheating. Pulling a little line pressure when hot helps keep it from banging upshifts that are fine on a cooler engine.

Now that I'm reading engine temp I'm able to run the electric fan as well. So this evening I pulled my fan clutch off and stuffed my electric fan in its place. The first challenge that I knew might be a problem was that the speed control box interfered with the a/c compressor about 10mm. Figures. I get under the car with the biggest prybar in the shop and proceed to bend the radiator support forward to gain enough room. Eventually it fits but the radiator now sits several mm lower. Not enough to be a problem.

I had procured the fan harness from a 211 wagon and its positive lead went to the junction block near the battery with plenty to spare. The heavy negative lead goes to a ground point near the abs pump. I tied my circuit 15 lead to a fuse in the box. I'll come back later and connect to an un-used fuse to do it properly. I tried to use a voltage divider but I wasn't getting speed control. Turns out that 300 ohms to ground gives the required PWM 3V that I need for control. Eureka! It works!

I did have an issue with the two piece fan shroud. Mounting to the radiator in the car put more and different flex into the assembly and I struggled to keep it from rubbing. Eventually it came off and it doesn't seem to be any worse off for it.

By the time I finished a rainstorm had passed and it cooled off quite a bit. Lots of hot temps in the forecast though. I'll have to dial in the table to get the least amount of fan speed to hold temp. The way its set up the TCU gives me a PWM point every .33 volts at the coolant temp sensor. This is quite a course window to try to control the fan over. I'm only able to use 3 of the 16 points for variable control. This will work I'm sure but it would be nice to get more PWM points over the usable range.

Recently I put a new thermostat in and blew the crud out of the radiator and condenser. I was still having the high speed fan cut in at 110 degrees C in stop and go traffic. I'm anxious to see what it will do now with a 600 Watt electric fan.

duxthe1 · #13 06-29-2016, 09:27 PM

I had ample opportunity to test the fan today in 88F temps. In stop and go traffic the car can hold 90 degrees C. Previously the same conditions would run 105 to 110 degrees C. While 90 C is a huge improvement it could do even better. Currently holding 90 requires about 75% fan speed. This is enough to cool the radiator to near ambient but now the limiting factor is the volume of coolant flowing at idle speed. Within seconds of running above idle the temp will pull back down to 87-85 degrees. My next move is to try to improve coolant flow at low RPM. I may try to fabricate an overdrive pulley for the water pump.

The coup de gras was running the a/c on the drive home from work. The a/c only added a few degrees. Any less and you wouldn't notice it on the gauge.

Speaking of a/c the a/c compressor drags down the engine enough that the shifts skew noticbly harder. I'm not using my calibration 'B' and now that the a/c is actually usable in the heat I may use cal 'B' to give me a decent shift table with the a/c on. Right now my engine only has just under 30 kpa between idle and full load which is barely enough to build a table from. The a/c soaks up half that so I don't think building a table from 15 kpa is workable. Going to have to revert back to TPS as the load axis for the calibration 'B'.

MAP works so much better.

duxthe1 · #14 07-21-2019, 12:18 PM

The 124 electric fan got a significant upgrade. Previously, I was controlling it from the PCS transmission module as a pulsewidth output based solely on engine temperature. It worked, and worked quite well, but I wanted more flexibility. Additionally I wanted to get rid of the auxillary fans in front of the radiator, and in doing so the main suction fan would have to take on the responsibility of cooling the A/C condenser. In order to pull that off I'd have to build my own fan control module. Thus the update....

The module is Arduino based and through a CAN interface shield I connect to the PCS transmission controller. Over CAN I read engine temp, throttle position, engine speed, and vehicle speed. Additionally the module natively reads ambient temperature, refrigerant temperature and a compressor enabled signal.

The CAN shield is a Chinese clone running 8MHz, and using the coreyjfowler library it reads the PCS network without any issues. The PCS controller broadcasts its own proprietary CAN messages and they thankfully have freely available documentation on the messages and addresses.

I use the throttle position data to cut out the fan over 95% throttle. When horsepower counts, you can't be lugging against the alternator, of course. I use RPM to disable the fan below idle speed, essentially preventing the electrical load of the fan during cranking. I use MPH to dial back the fan once the vehicle is traveling fast enough that ram air is available for cooling. I still need some highway miles to tune that function.

The module reads ambient and refrigerant temps directly. I use the same ambient temp sensor that Mercedes has used for the past 20+ years. I've just got a small metal bracket holding it out in front of the condenser for now but am going to experiment with placements to try to get as little heat soak as possible when the car isn't moving. I use a Mercedes refrigerant temp sensor as well. It swapped right in place of the high temp switch on the receiver drier. It should be noted that these two sensors have entirely different sensing elements and required two different functions to calculate temperature. With the compressor enabled I compare refrigerant temp against ambient temp. As the difference increases, fan speed increases. I also add or subtract fan speed in very hot or cold ambient, respectively.

The Arduino controls the fan by pulsewidth, and thanks to a handy PWM library its possible to directly output the 10Hz frequency required to run the fan without any processing overhead. Once the function is called the pin outputs the PWM and the program gets on with other business. The fan itself is controlled by the duty cycle with 10% being off, and 90% fully on, with 10% steps in between giving 8 speeds. The program compares engine temp against the setpoint and assigns an error value. It also calculates an error value for refrigerant temp as well as add or subtract error for the other variables. This error value is then correlated to fan speed request. The Arduino IDE has a serial monitor window allowing me to use the laptop and readout the data in all the variables and calculations enabling me to see what the program sees in real time. Very handy for fine tuning the parameters.

Aside from better fan control I'm really excited to have the original aux fans and shrouding removed from in front of the condenser. When I pulled it apart there was a good 3 inches of leaves, feathers and trash in the bottom of the aux fan shroud. I expect that not only engine temp regulation but also A/C performance will be improved.

SpartanV · #15 07-23-2019, 02:00 AM

That's cool 😎

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