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Discussion Starter #1
I just built a DIY MS3 / 3.0 kit, and I built my own harness connector from a Ford Rotunda system. It actually started the car first try today, surprisingly. I didn't connect up any fan wiring yet, so I couldn't start tuning my car.

I think the best idea is to use the PWM IAC outputs to control fan high and fan low. I want to keep the spark outputs available for when I pull the distributor out.

I found this diagram but I'm sure the high speed fan control pin on the ECU is wrong:


My 95 service manual shows pin 55 for low speed control and pin 32 for the high speed (not 52 as in the diagram - that's shift solenoid #2 in my Ford manual!).

If I pull 32 low, I should get high speed. Sending 55 high should get me low speed, looks like there's some additional control in the CCRM to invert the signal there. Unsure why Ford made the two controls opposite.

I know DIY's PNP harness has fan control, so it should be possible. I'll update this with what worked, unless someone knows.
 

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You will not get true PWM fan control (i.e. variable speed) when you still must use relays for high & low speed. The SN95 fan draws too much current for any Megasquirt to provide variable speed. You will have 2 speeds & no soft start.

I much prefer a separate PWM soft start controller. Easier on the alternator & the rest of the electrical system when the fan kicks on. The inrush current on these fans with no soft start is 100A. That alone can cause the system voltage to drop low enough causing the Megasquirt to crash.
 

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Discussion Starter #3
That is something to take into consideration. My electrical system dealt with the fan pretty well, it rarely ran high speed. I don't have AC and I have an SVE aluminum radiator.

Poking around Tuner Studio and the docs, I found you can setup PWM vs CLT as an output. I ordered some cheap solid state relays rated at 40A, that will even take a 5V input. It will be an interesting experiment.
 

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The low speed fan is wired to come on with the key. When the computer is on, assuming engine temp is below threshold, it provides a ground to the low speed relay to remove power from the fan. This default on is a failsafe.

They are both controlled by sending low, but you're right the effect is opposite.

The high speed fan works the way you would assume it does.
 

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Discussion Starter #6
Incoming ramble:

Seijirou is correct, grounding 32 is high, grounding 55 turns off low speed. If you leave the wiring to float, you get constant low speed.

I did have success with a solid state relay setup, but you can't cheap out on the relay (as expected).

AOLE ASH-40DD $12 (40A rated) - Worked but was getting so hot I shut it off, you may be okay driving a sub 10A load with this.
Fotek SSR-40DD $8 (40A rated) - Blew it up before I could check any temperatures

Winner:
Crydom D1D40, ~$85 - rated for 40A with a 106A surge current rating

A freewheeling diode is a must here, I used this circuit flom Blown88GT's helpful tech note:


I originally tried a 3W 28V zener across the relay terminals but there is so much energy to dissipate from the fan turn off it smoked immediately. What worked is a 15SQ045 setup like Fig A. This diode is a 15A high surge, schottky barrier type. Diode isn't special, it's just one I had on hand.

As your PWM frequency increases, the diode takes more turn off events making it run hot, as PWM frequency decreases you'll lose the ability to run the fan at low duty cycles. 30 to 60Hz worked fine for my fan, even down to 5% duty cycle. Diode was generally running 30F above ambient.

I don't have any equipment to measure >20A DC. I'm guessing this fan draws 30A. I'm going to borrow some equipment so I can measure inrush and constant draw. The crydom was dropping about 0.75V across its terminals, fan moved plenty of air - but this may be too big a loss for something like a fuel pump controller. Heatsinking and heat sink grease is a must, I was using a aluminum plate but I'm going with a Bud die cast aluminum box for under the hood. I want to mount it where it will get some air flow.

$85 isn't cheap for a relay, and it's getting close to what you can buy a fan controller for. I picked up my crydom relay as "new old stock" on ebay for $30 because I like to gamble. The date code on it reads from 1997 so it's almost as old as the car. Will update with measurements and we'll see in summer 2019 if it blows up.
 

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I used a 1N5404 for the freewheeling diode, even when I was using a Bosch motor rated 75A relay. Ford used a number of diodes, there's one across the A/C clutch. The SN95 fan is close to the Mark VIII fan. The Lincoln Mark VIII fan will draw continuous currents of [email protected] & [email protected], and has a starting current in excess of 100A. Even with the 3G 130A alternator, when the fan would turn on, the idle would drop momentarily & sometimes the engine would die.

This is why I went with the DCC FK-35 PWM controller. Newest version is the FK-50. Derale licensed the patent from him, so their's uses the same design.
 

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Discussion Starter #8
Measured current at 40Hz, 50% duty cycle. It's surprisingly high. I'm using a 1 milliohm shunt for measurement and I'm going to have to verify it. Bottom trace is straight measure, top is scaled and filtered slightly. I'm seeing currents around 47A to run the fan.

 

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That relay is pretty slick.
 

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It's what I used before the PWM fan controller. 1st one was Variflow, then the DCC. Same inventor, different design & company. I still have the relays & one of the same model without the clamping diode across the relay's coil.
 

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Thinking out loud here, so feel free to pick this apart.

It seems some mid/late 2000's volvos come with a PWM controller on the fan itself. Can probably find one easily in a junkyard, but here's a new one just as an example.

https://www.ebay.com/itm/Engine-Cooling-Fan-Module-Relay-Controller-For-Volvo-30680547-30749759-30680512/223053148290?fits=Make:Volvo&hash=item33ef00f082:g:IFsAAOSw4apbQyJM

Seems like a pretty simple setup in terms of wiring. Obviously the biggest question is how much current it can handle. I'm running an 95 V6 fan which is single speed only on a fox mustang, and i've measured approx 25 amps continuous when running. I forget offhand the starting current but i can measure that.

Quick searching around, i see the Volvo models equipped with the above controller use a 60A fuse for the radiator fan.


EDIT:
Here's the vid
 

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I like that. Please update if you end up trying it. Some day I'll be able to get back to fiddling with my car.
 

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Discussion Starter #15
I ended up finding one locally and bought it.

I'll play around with it a bit and update if I make progress
Nice, this was my next step if I burn up the crydom relay I have. There's a lot of OEM units out there to choose from.
 

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I ended up finding one locally and bought it.

I'll play around with it a bit and update if I make progress
If it doesn't work out, just get the DCC from Brian. Tell him I sent you. He doesn't get busy until the summer when he gets overloaded with orders.

BTW, he uses a green fuselink to connect the DCC to the battery. Do not use any old 60A fuse, it must be a slo-blow or a green fuselink.
 

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The Volvo fan controller looks like this one
Santech Cooling Fan Control available from AutoZone for $189.
 
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