As of today I have the Mark VIII operating reliably (At least so far). Wired a 40amp relay (Which I am fairly certain will fail but it was the highest amp relay available to me) and a switch to operate the fan manually. I'll will probably order the painless unit at the end of the week.

 

That should work for you as a single speed fan until your other unit arrives. If your fan motor is wired for 2 speeds, on high speed, it uses a bit over 30 amps continuously and a bit over 60 as in-rush at the start. If the wiring will handle the continuous run amperage, it should hold up for the starting current - it's only there for about a second. If the relay has problems, you can always add a solenoid the way I've shown in the schematic I've posted - the solenoid doesn't take that much to engage and with the next gauge up in wiring would easily handle the ford fan motor. I show some "fly back" protection diodes in the schematic - with a relay system, you shouldn't really need them but I consider adding them cheap insurance. The PWM system will most likely have them built-in to protect the unit (as well as the rest of the truck electronics).

PS, if your fan motor is wired for 2 speeds, using the controller you had wired up to it earlier should work if you connect it's output to the low speed fan motor wires (leaving the high speed disconnected). That fan pulls around 3000 cfm in low speed (should be enough for your truck) and amperage wise, should fall below the 30 amp rating of most controllers. There's a write-up on this site somewhere that talks about using a SPAL controller on a Ford Taurus fan, but wired up to feed it in low speed only.

 

I've been running the same Flex-a-lite 31149 controller for 8 years with the MarkVIII fan on low speed and have never seen the temp go over 200* even in stop & go traffic with the AC going full blast and outside temp @100*. The fan is amazingly efficient and does a hell of a good job cooling my 5.9L.

 

My fan doesn't seem to have 2 speeds. Both wires spin at the same rate. I don't know if maybe I need to supply more power to the black wire on the harness or if it's spinning at full speed. Either way the controller couldn't keep the fan going using either wire for more then 2 - 3 minutes which I think might have something to do with the soft start feature of the controller.


Going through different threads some years of the mark 8 fan have a a/c lead (which mine does) to turn the fan on when the a/c kicks on then the other wire is controlled by coolant temp so again I might not be supplying enough power to the fan to get the full speed.

 

I had assumed that they all would have had roughly the same configuration, but after a bit of research I see that there are several versions of the Mark VIII fan, and I would suspect that the newer ones would have been designed for a more up-to-date control system. In your case, I would check to see if any of the local auto salvage yards had any Mark VIII that was 2 speed or a Taurus fan and use your current controller on the low speed - that would probably be cheaper than buying the Painless controller (some of the U-pull places sell them for under $50).

 

I installed a thermal switch today which switches on at 190 and off at 180 which so far is doing the trick. I did notice the condenser was smoking/steaming before the fan kicked on. I'm assuming that's normal when the a/c is running with no airflow after a heavy rain that definitely soaked the condenser?

 

I think so, like tarmac steams on a hot day after the rain. I'd keep an eye on it though just to be sure.

 

I assumed so but wanted to ask, terrified me when I first saw it.

 

You will definitely want to wire in a relay to power up the fan any time the a/c is running. If not you could take out your compressor from running too high of pressure with no air flow over the condenser.

 

Can someone shed some light on how to wire a relay so it triggers when the a/c is turned on. I've checked both sides of the plug, both provide ground when the a/c is on or off. I have a feeling I'm missing something simple (I'm sure the beer isn't helping.)