[SCOTI]

Originally Posted by gmachinz

Yes-my fan harnesses differ from anything else you will find on the market-I worked (unsuccessfully I might add...) with Mark K. @ Spal some years back about designing a HD fan controller exclusively for the Mark VIII fan and other high output Motorcraft fans. I bought the OEM Motorcraft fans in large bulk from Ford for use in my relay harnesses I was building at the time for my shop customers. Well, two things happened:the fans went on the dis-continued list from Ford and Spal wasn't interested in building such a demanding controller for use with that or any OEM fan. Even their latest fan controller has an internal over current limit of 35 amps. If you try to run a fan that draws any more juice than that, it is designed to kick off.

Given what I know about fan motor efficiency I am not satisfied with any pancake style motor that Spal and most aftermarket companies offer so I was back to the drawing board. A rep for Siemens VDO out of Canada who designed/manufactured the fan motor for Ford informed me they (Ford) wanted a design that could run at full speed 24 hours a day for 10 years if need be...since that deisgn would see service in both high end Lincolns and police package vehicles. So I know from the horses mouth Motorcraft makes the most stout fans hands down.

Now, after reviewing the circuit design that Lincoln used on those fans called a VSC (variable speed controller) that they varied the speed by using a variety of capacitors of varying voltages to change the speed of the fan-not quite PWM but a more mechanical version of it. I figured the same thing could be accomplished through the use of a series of resistors to limit the voltage based on how many resistors the current must pass through-so I built a test harness and it has worked just like I planned from day one-I've perfected it over the last year and now, it serves as a conversion fan harness whereby it can allow you to take any fan-single or dual speed and use it as a 3-speed fan. My aim was to create a harness that can easily handle the demand of the Mark VIII fan since if it can do that, it can handle any fan you run it with, right? And, my relay resistor harness allows for 3 speeds out of it. Nobody else makes a non-PWM kit that can do that.

I just finished testing/running it on a dual 18" fan assembly from a 2010 F250 with the largest dual fan setup I've ever seen-it moves a reported 6000 CFM and pulls about 42 amps @ full speed to do it. I ran both fans at 3 speed in parallel and managed a 16, 28 and 42 on low, medium and high speed.

I did a kit from you years ago that used the MVIII fan/PWM controller. Is your current non-PWM set-up what you would recommend now? What were the core dimensions on the F250 twin fan set-up?

I installed a SBC serptentine set-up on my BBC in my dually. I upgraded the therm clutch fan to severe-duty & increased the fan diameter to as large as the opening in the shroud but I'm not sure how well it will cool yet as it hasn't hit the TX summer months. I'd like to have a 'plan-b'.