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Lusty 08-23-2012 09:52 PM

Wiring Help

I just bought a replacement blower motor for my furnace, and I thought I'd be able to do the wiring myself but it's not layed out the same way as my old motor was. My previous blower motor was set to always run, but it would spin up when the AC or the heat came on. My furnace is a lennox (circa 1978 or something lol). This is just to tide us over until the spring when we buy a new furnace.

Here are the wiring diagrams for the motor (the paper was taped to the motor)

Here is the motor, each terminal or post has a number by it. My old motor had HI or LO on it, so these numbers confused me a bit.

Now here are the old wires. I will replace or restrip them so they're not all mangled looking like they are in the picture.

So any help would be awesome. I don't want to connect something wrong and fry the motor. :huh:


Houston204 08-23-2012 10:47 PM

Post the furnace wiring diagram...

Lusty 08-23-2012 11:14 PM

Where would this be located? I've looked inside and out and can't find it. Thanks.

Lusty 08-25-2012 12:24 AM

OK so I hooked up the motor and it works - sort of. Since there we're only 2 connectors I put the 'hi' line to the number 1 terminal and the blue to the #4 terminal. The former'lo' connection I taped off and its not hooked up. Ground is hooked up as well.

The AC works fine it fires up the blower motor no problem and turns it off. The heat won't turn the blower on. If I set the blower to manual then I can circulate heat but it still won't control the motor. Having our blower on all the time on high isn't ideal.

Any idea what i can try? There is no wiring diagram on my furnace. Its old and someone added an AC unit to it so there are wires everywhere.

I tried hooking the 'lo' line into the #1 spot but the motor w
Wouldn't turn on. I'm thinking it might be neutral/negative? Should I combine it with the blue wire?

Thanks guys

biggles 08-25-2012 04:06 AM

the new motor is single speed HI only with 2 wires landing on those terminals the heating and AC are 2 different speeds..keeping in mind the heating supply fan runs thru the furnace heating cycle not the many wires did the old motor have on it?

beenthere 08-25-2012 08:32 AM

The low line should run the motor for a heat call. So when you had it connected, did you run the furnace in heat mode? If not, try it in heat mode. If it works in heat mode, you will need to combine the high and low wire both to terminal 1. Using a pigtail is easier then putting both wires on one terminal.

Lusty 08-25-2012 10:10 AM

The old motor was a variable speed. The picture of the wiring above shows where the old wires went. I tried to combine both the hi and lo wire but it just blows the breaker.

Yes when it was connected previous it ran in heat mode perfectly. The AC worked as well. I don't think it's the fan limit controller.

beenthere 08-25-2012 10:14 AM

Your old motor was a 2 speed, not a variable speed.

Use a multimeter, and check each wire to ground for voltage. Yiou'll need to turn the fan to on to check the high speed wire, and then you'll need to run the heat to check the low speed wire.

Also, trace out each wire to its source.

Lusty 08-25-2012 04:23 PM

Ok I will track down a multi-meter and check back. Thanks.

Lusty 08-25-2012 06:51 PM

Ok so I managed to get it to work (sorta). I hooked up the old HI line to the #1 terminal and the old LO to the #4. I changed my fan setting to "on" on the thermostat upstairs and started the heat up. I can see the Fan Limit Switch rotate as the furance is heating up and the blower motor fires up after a minute or two. The problem I'm having now is once the blower motor kicks on immediately the burners turn off. I have my limit switch set to 90 / 130 / 200. These are the recommended settings for my limiter. It's like the fan isn't turning on when it's suppose to and the limit switch is turning off for the same time the blower motor comes on. So now I'm really confused. I'm not worry about the AC working this year, it's going to be winter soon anyway.

Any ideas?

beenthere 08-25-2012 07:15 PM

Some where long the line, the furnace was miss wired. Would need to kn ow where ll the wires go to.

Lusty 08-26-2012 06:33 PM

So here is the fan limiter wiring. The old furnace blower was set to run all the time, on low speed. I can force the fan on by selecting "auto" on my thermostat and the fan runs constantly. It doesn't shut off. I can leave the fan running 24/7 and get heat but it's less than ideal. If I turn the thermostat to "on" it shuts the fan off and it won't come on when it's suppose to.

Here is the picture of the other wiring. I'm not going to open it up and take a picture until I get a multimeter and ensure I don't get shocked.

beenthere 08-26-2012 07:01 PM

The blue wire should run to the fan relay and go through the normally closed contacts, and the black wire for high should be on the normally open contacts. Since you now have a single speed blower, you will need to pick the blower speed you need that will be good for both heating and cooling. And then up the fan relay so that the fan limit or the fan relay can bring the fan on.

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