direct drive fan motor

[Micky]

I have an old furnace with a one-speed-at-a-time-based on the wiring fan motor.

I once rewired it, using the schematic, to see if I could find a lower speed, so I know the schematic is correct, but in my dotage, I can't understand it!

It calls it a "direct drive fan motor" and it has 4 wires coming out of it. It appears that either 2 or 3 wires are to be connected at a given time, although that doesn't correspond to my vague memory. The wires are:

White Common, connected at all times Black High, perhaps connected at all times, if you go by the schematic Blue Medium Red Low

The schematic shows 2 wires connected to the motor and a iiuc a 3rd optional wire.

[bob_villain]

...do you have *any* search abilities?

[trader_4]

What's unclear? It has three possible speeds. If there are only two wires going to it, pick you speed. If there are three wires going to it, then one of those is for heat and one for cooling. Typically cooling is on high, heat would be on medium.

[Stormin Mormon]

It's been a year or so since I wired one of those. The one I did, the circuit board had terminals labelled HEAT, COOL, and PARK, if memory serves. The one I did, had red on heat, blue on cool, and black was on park. The family wasn't getting enough AC in the second floor. I changed the AC blower from medium to high.

In your case, sounds like you may wish to take blue off HEAT, and put it on PARK. Take red off park, and put it on heat.

Remit $74.50 for internet consult, please.

[gfretwell]

You only use white and one of the others for each speed

[jamesgang]

Sometimes those are used in an air handler that has both ac and heat. The fan speed may be high for ac but one of the lower speeds for heat.

[Tony Hwang]

Right cold air is heavy so needs high speed to push.

[Micky]

If that were the case, that would be certainly make it unclear to someone who didn't expect that, who had never seen a fan motor hard wired for two different speeds.

But, no. There is no separate heating and cooling speed.

The schematic is unclear, perhaps incorrect in this one small part, but I did't post this when I wrote it because I figured out the rest of the fan relays and enough of my memory came back that I lost interest in the details of the fan.

[Micky]

I'm sure that's right. Long ago I tried the other speeds, on the faint hope that one would be slower than what I had, but I had the slowest, as the color indicated. (So I started closing the bedroom door when the AC was on. Strangely, I've never wanted to close the door when the heat is on, even though it's the same fan speed. Old furnace.) The schematic seems to show that 3 wires from the furnace are connected to the fan, but I don't think that's so.

[trader_4]

It is the case and it is clear to everyone reading this, except you.

So then it's as simple as can be. Put the one wire on the speed of your choice.

[trader_4]

And I'd be surprised that low speed is optimal either. Never seen an AC that uses low fan speed for cooling.

[Micky]

It's good that you know about everyone else, when you haven't even seen the schematic yourself.

That leaves 3 wires from the furnace connected to the motor.

[trader_4]

You posted this:

"I have an old furnace with a one-speed-at-a-time-based on the wiring fan motor. "

"The schematic shows 2 wires connected to the motor and a iiuc a 3rd optional wire. "

That would imply that it has only two wires and runs at only one speed. IDK what "one speed at a time" means, otherwise. Fans with 3 speeds can only run at one speed at a time.

"But, no. There is no separate heating and cooling speed. "

Are you as sure about that as you are the number of wires? It would seem odd to run wires for two speeds to the fan motor and not use them.

[Micky]

You only quoted part of what I wrote.

And no, it implies that the schematic shows it has 3 wires, but that I don't understand how it can work with three wires.

Why don't you just skip this thread and go on to something else.

[trader_4]

I quoted what defined the number of wires and connection. What the schematic shows is one thing. How it's actually wired is another. It wouldn't be the first time a schematic was for various models and the particular model you have doesn't use all the possible wires. So, what is actually there?

Why don't you learn how to make one complete post with all the information? Many people here have tried to explain it to you based on the info that you provided, but apparently it's not sinking in. With three wires you get two speeds.

"And no, it implies that the schematic shows it has 3 wires, but that I don't understand how it can work with three wires. "

One for high speed for cooling, one for low or med speed for heat, one neutral. 1+1+1 = 3 Got it now?

[clare]

My old furnace has a 3 wire motor. Onewas common, one was "constant run" (1/6 HP, 600RPM more or less, and the other was full fan - for heating/cooling. On most furnaces they would be set up that when the furnace calls for the blower to come on it switched from low to high.

On mine, the low was run full time, and the high came on with the low for normal heating/cooling. It worked that way for years, even though it was not the proper way.

A lot of newer furnaces have multi-speed direct drive motors. The HVAC guy selects the speed that produces the specified heat rise for heating, and the specified temp drop for AC. That will virtually always be 2 different speeds, and will deprnd on the static pressure in the ducts (in other words how much restriction in the system)

The motor in yours is likely designed for use in a furnace / central air handler combination that allows for separate heating and cooling speeds, or a constant run fan. If there are 4 wires it could support both.

My new one has a 3 phase brushless DC motor with variable speed drive controller.

[Micky]

That would explain it. It's just not used to its full capacity in this furnace. Thanks.