I replaced my old HVAC system and a friend suggested asking the HVAC company to leave the fan unit to use as a shop fan. I thought it would be a simple task to add a plug to the motor and off it would go (or rather on...).

I've tried wiring black-black, white-white (there are multiple blacks & whites) with no luck. I appreciate your time!

Here are some relevant pictures. Fan Housing Label

Motor Label Wiring Harnesses

  • I have been told that the fan output or input must be restricted to load the fan motor or it will overspeed and fail. I was told to put a restrictor plate over the output side that covered about half the area. This was decades ago and I don't know if modern HVAC air handler motors have built-in circuitry to control speed. Oct 11, 2020 at 10:14
  • I read the same thing and had planned on doing that once I had the fan working. I figured it should at least start without the restriction being in place, no? Oct 11, 2020 at 10:24
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    Not that the wiring diagram is overly forthcoming for your application, but it's pretty clearly not 120V per that diagram. "Plug 3" gets 230V on black and yellow, ground on green, per that diagram. Then you get to have fun figuring out what you need to do with the wires from plug 4 to make it run, if that's possible without the circuit board.
    – Ecnerwal
    Oct 11, 2020 at 14:04
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    @JimStewart Read the diagram. They are not very forthcoming about the control logic, but the power wiring is crystal clear, and not 120VAC.
    – Ecnerwal
    Oct 11, 2020 at 15:54
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    @JimStewart I notice the labels in the "programming" area of the PCB drawing mention AC/HP (air conditioning/heat pump) and AUX HEAT KW. I'm inferring this is not from a fuel-burning furnace but rather a heat pump with electric auxiliary/emergency heat. Given the electric heat in the same cabinet would be 240V it makes sense that the whole unit could be designed for 240V.
    – Greg Hill
    Oct 12, 2020 at 14:08

1 Answer 1


To me that looks like an ECM motor -- an "electronically commutated motor" or "brushless DC motor." This is a newer motor technology with a variety of benefits.. at the cost of being more complex. These motors can't run directly from a power source; they require a control system to operate. The good news is that yours appears to have that controller built into the motor.

Based on what I see in the wiring diagram I'd suggest keeping that PCB in the circuit too. It appears the PCB provides a convenient way of "programming" the controller's behavior -- things like how fast it should spin (implied the the choices of AC/HP size and AC/HP CFM adjust) and how soon it should come on and how long it should stay on (ON/OFF delay).

I've not had the pleasure (?) of working on one of these motors myself, but from what I can gather online (and considering there's no 230 V connection shown to your PCB), all those control signals are probably 24 V ac signals. It's possible you could have damaged the controller by connecting 120 V between pairs of black and white wires, but.. it's also possible the internal control was engineered to survive that kind of mistreatment. Though you probably could connect 24 V ac to some of the wires on plug 4 and get results, it seems much easier to keep and use the PCB.

Try feeding the motor and the transformer 230 V (or 240) on the black and yellow wires and put a jumper between the R and the G terminals. Be prepared to wait up to 30 seconds depending on how that ON/OFF delay setting works. If you get a response from the fan in these conditions you could experiment with the other programmable settings for CFM, delay, etc.

  • I appreciate everyone's time, input, & advice but the ROI for me doesn't seem to be there. I was hoping for a quick way to hook up to 120 and it doesn't seem there is a way. I hate throwing perfectly good things away, but it looks like I'll have to. Again, I appreciate the assistance. PS. If anyone wants it I would ship it for cost or local pick up in Independence, KY. Oct 12, 2020 at 13:20

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