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Discussion Starter · #1 ·
I have a 2017 F150 with a 3.5 EB. The truck did not come equipped with a tow package. It has the 2 speed relay controlled fans. I have decided to swap the fans for the more powerful variable speed fans. I have done some research and this is what I have so far.
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173137

It appears that for the relay controlled fans low speed setting is achieved by activating relay 1 only. This causes both of the fans to run in series. High speed is achieved by activating all 3 relays. This causes the two fans to run in parallel. This cuts the resistance in half and doubles the current to each fan. For the variable speed fans relays 1 and 3 are activated any time the key is in the on position.
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This supplies the positive voltage to the fan motors through pin 3 . Both fans are also connected directly to ground through pin 1 and the fan is controlled by the PCM using PWM through pin2. The wiring changes are pretty straight forward and there doesn't appear to be any additional modules needed to run the fans. The last piece of the puzzle is the change within the PCM to run the new fans. I found a similar truck to mine, except that it has the variable speed fans, and used the vin to download the As Built data from the Motorcraft service website. I compared that to the As Built data from my truck to try to see if this was something that could be accomplished using Forscan, but have not figured this out yet. Here is a link to the excel file that I created to compare data. As Built Data Any help would be appreciated. If It cannot be done with Forscan, I am considering building a stand alone module to control the fans.
 

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2021 Powerboost Platinum FX4 Kodiak Brown
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Wow

Very nice FIRST post!
Sure hope you keep it up. :)

Sent from my SM-G988U using Tapatalk
 

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I have a 2017 F150 with a 3.5 EB. The truck did not come equipped with a tow package. It has the 2 speed relay controlled fans. I have decided to swap the fans for the more powerful variable speed fans. I have done some research and this is what I have so far. View attachment 173136 View attachment 173137
It appears that for the relay controlled fans low speed setting is achieved by activating relay 1 only. This causes both of the fans to run in series. High speed is achieved by activating all 3 relays. This causes the two fans to run in parallel. This cuts the resistance in half and doubles the current to each fan. For the variable speed fans relays 1 and 3 are activated any time the key is in the on position. View attachment 173138


This supplies the positive voltage to the fan motors through pin 3 . Both fans are also connected directly to ground through pin 1 and the fan is controlled by the PCM using PWM through pin2. The wiring changes are pretty straight forward and there doesn't appear to be any additional modules needed to run the fans. The last piece of the puzzle is the change within the PCM to run the new fans. I found a similar truck to mine, except that it has the variable speed fans, and used the vin to download the As Built data from the Motorcraft service website. I compared that to the As Built data from my truck to try to see if this was something that could be accomplished using Forscan, but have not figured this out yet. Here is a link to the excel file that I created to compare data. As Built Data Any help would be appreciated. If It cannot be done with Forscan, I am considering building a stand alone module to control the fans.
You are correct on how the two speed fans work. This is how they were all the way back until at least 2011 and maybe before that.

I have HPTuners which allows you to alter the fan tables. The thing is the fans tables seem to have always been set up like they were meant for PWM control vs just being off/lo/hi. This is the Fan table vs coolant temp table for a 2018 raptor:

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Here is the same table for my 2014:

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So they have essentially been set up the same way all along and I wonder if it is just a matter of you plugging it in? There is no setting in HPTuners to switch from 2 speed to PWM.
 

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Discussion Starter · #5 · (Edited)
mass-home...Thanks for the tables, they may come in handy if I have to build my own control module. I don't believe that I can just rewire the fans for a couple of reasons.
1. With the off/lo/hi fans, the PCM controls the relays by providing a ground source for the control side of the relay. It also uses separate high and low speed circuits (FC1 AND FC2).
2. With the variable fans, the PCM controls the fans directly by providing a 12V pulse. This only uses one circuit (FC1). FC2 is left open. Without some type of a PCM change this is going to throw a DTC.

The fact that the fan tables are present is a good sign though.
 

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If the signal is pwm, then even a home built module would be doable for $30 and a MOSFET or two. But forscan programming would indeed be key. Or you could go halfway and use the 0/1/2 signaling and build a controller that did basically the same thing, 0, full, and a low speed which you determine yourself. Is the new fan motor a simple +/- or is it more like a 3-phase stepper?
 

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Fantastic, I enjoy when people bring their knowledge to the table. This is great!

Welcome to the forum, you will fit right in here.
 

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Discussion Starter · #8 ·
Meep.... I originally considered creating 2 circuits like this one, one for low and one for high.
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It is a simple square wave generator. By altering R1,R2, and C1 I can set the duty cycle. I could use the current relay circuits in the truck to power my two pulse generators. This would allow me to have off/lo/high. This type of control defeats the whole purpose of the variable speed fans. The better approach would be to use a microcontroller that reads the ECT sensor and A/C clutch signal. Then it could calculate the desired duty cycle programmatically. If I can't figure out how to get the truck's PCM to control the fans, I think I'm going the microcontroller route.
 

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Meep.... I originally considered creating 2 circuits like this one, one for low and one for high. View attachment 173198

It is a simple square wave generator. By altering R1,R2, and C1 I can set the duty cycle. I could use the current relay circuits in the truck to power my two pulse generators. This would allow me to have off/lo/high. This type of control defeats the whole purpose of the variable speed fans. The better approach would be to use a microcontroller that reads the ECT sensor and A/C clutch signal. Then it could calculate the desired duty cycle programmatically. If I can't figure out how to get the truck's PCM to control the fans, I think I'm going the microcontroller route.
I love it! agree… completely. You’re on it. and yes, theres more to be gained by going true pwm/variable from the ecu and forscan. a couple of questions?

1. I’m not too familiar with the 3055 but the internet suggests the 3055 is only rated for 15A. I’d expect the fan could pull 3 times that plus surge. I’d highly suggest something a bit more robust.

2.One thing I’d suggest if you were to go in the above direction… and forgive me I wasn’t school-trained so idk the proper term… but I’d highly recommend a diode on the output to drain inductance feedback the fan motor would send back to the power section when it goes open in the cycle. It will increase its resilience and lifespan. think about it… when it’s sending 20 amps into an inductor (motor) and you immediately cut the circuit open, what happens? Some high multiple of inductance surge (think buck boost converter?) feeds back, and the transistor is left blocking 80V every cycle, which beats it down over time. Forgive me if I’m assuming you don’t know this - clearly you’ve got a solid grasp on things.

nice work!
 

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Discussion Starter · #11 ·
Meep.... This is exactly what I was hoping would happen. I like having like minded people to help me think through the process. Here is a little more info about my setup. The fans that I am trying to install are the factory f150 variable speed fans. They are 700 watt brushless units with a built in controller. (Part No.: HL3Z-8C607-B) They have 3 wires connected to them. The first is the power wire which comes from Relay 1. It is a 10 gauge wire with a 50 amp fuse. The second wire is the control wire. It comes directly from the PCM and is only a 20 gauge wire. It doesn't supply any power to the unit, only the control signal.

I copied this paragraph directly from the Ford Manual.

The PCM controls the fan speed and operation using a duty cycle output on the FCV circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor).

The third and final wire is the ground which is a 10 gauge wire like the first one. The wiring is simple to modify and I have already found the necessary OEM plugs. The only thing that I am still uncertain of is how to modify the PCM for the variable speed fans. I had a few moments today to play with FORscan. I was able to manually turn the fans on low and high using output control mode. I was also able to select a desired duty cycle and get the PCM to generate a PWM signal that I verified with my oscilloscope. The PID to select a desired duty cycle is located in the PCM Module. Then I went to the As Built Data for the PCM Module and noticed that the module location is 7E0. I believe that the necessary changes with be within this module. I have the As Built Data for a similar truck as mine, with the exception that it has the variable speed fans. I am in the process of comparing the configuration data between the two trucks to look for differences. Then I guess I will copy and paste the module configuration data one line at a time until I figure it out.
 
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