Of all the threads on wiring this fan, I cannot seem to find one that references using both speeds. I have a 2 speed fan control unit that powers speed 1 at a settable temp and then kicks on speed 2 at 10* hotter. Sounds great. Just run the signal for each speed to the 70 amp relays for each speed and its good to go. WRONG! Unfortunately, the controller does not power the high speed independently of the low speed. In other words it send power to both at the same time when the high speed temp is reached. On the Taurus/Mark VIII fans, thats a problem. How can I wire this so that when the high speed fan comes on, the low speed fan turns off. All the wiring diagrams I find have 5-pin relays. I have 2 4-pin relays. My thought is to run the high speed signal wire to the GRND terminal on the low speed relay and "daisy chain" it to the high speed input on the high speed relay. When the high speed signal comes in, the low speed relay would then lose its grnd and shut off leaving only the high speed fan running. Would this work or am I asking for trouble? Thanks
Think you need one 5-pin relay. Use the controller to run only the low speed. Wire the center (hot when relay isn't activated) pin to the controller relay so it can switch on only if the high speed isn't running. Switch the 5-pin relay with a temp sensor for the high speed. Use the switched power from the 5-pin relay to power the high speed. That way the low speed gets switched off if the high speed is running. That's how I used a single speed controller plus another circuit to run both speeds on the Taurus fan. The only diagram I have is a crude one I sketched on a piece of paper.
LOL. Love the pic. Looks like the back of my work orders trying to explain myself to our service writers. As for the fan issue its a common issue on here. I ahve a different set up on mine but I'm sure your issue will get solved fast.
I think I am going to get a small 5-pin relay to control the low speed fan signal. I'll use the high speed signal to interrupt the low speed circuit. it will look like this: 86 - Ground 85 - Low Speed signal wire input 87a - Low Speed signal wire output 30 - High Speed signal wire input 87 - High speed signal wire output The relay will receive its constant power (85) from the low speed wire and pass thru (87a) to the low speed 70 amp relay. When the high speed signal wire (30) energizes, it then flips from low speed signal output (87a) to high speed signal output (87) to the high speed 70 amp relay. Therefore no longer powering the low speed relay. I'll try it. If it works I'll try drawing up a diagram.
you know... after my last post, I went back reread your suggestion and now I think we are basically at the same conclusion. For some reason, your idea didnt sink in to my clumsy little brain.
Maybe because there's an extra relay in the drawing. I think I put the 4-pin relay for the hi speed fan in the circuit only because I couldn't find a 5-pin that would handle the 60 or 80 amps required for the hi speed.
