mobilehomerepair.com

Hello,

I have a problem.

I have a Coleman 7966-856 Furnace and when the furnace calls for heat it fires up. I hear a click after a bit then nothing at all after that. The blower motor does not start and the furnace shuts back down.

The blower motor is new and it does work. Right now, for tonight, I had to wire the motor to start manually. I can't get anyone to come out tonight.

Ok, so I grabbed my multimeter and start checking. The lower limit has power on both legs. I then check the fan switch, power on one side. The click I heard was the fan switch. I tried to fire up the furnace again. After a bit I heard the click and then I tested the other leg of the fan switch, I had 110v, but the blower motor still didn't start. That's when I noticed the humming coming from the motor. I checked the wires from the motor and both showed 110v.

I can't figure this out at all. Right now I am manually starting the motor with a switch hooked into 110v. But get this when I turn the switch off I can still here the motor hum. I carefully reversed the wires to the motor but nothing changed.

Any idea what's going on?

The motor is an A.O. Smith S1-7966-311P

Edit:

I have the manual power switch wired into the power coming into the furnace, when I hit the power switch on the furnace the humming from the motor stops. I am watching this carefully.

Does your furnace have a booster motor? A general parts drawing shows one, but the parts listing doesn't list it. A booster motor is a little motor off to the side that starts to run before the burners light bringing air into the combustion box? You may not have it.

Anyway, hang on. You need Robert or Hvac1000 to help you, and one of them should be here yet tonight.

Mark

I don't see any "booster" motor. The owners manual does not show anything.

Thanks for the help. Right now we do have heat but I have to fire up the furnace then start the blower manually. I just don't understand There's power, the blower is good, the switches seem to work, but the blower refuses to start, it just hums.

Thank you for the help I appreciate it, I'm just glad there's heat for the night.

Need pictures? I have a camera sitting right next to me.

Hi,

Do you have a wiring diagram ? If so, can you take a pic and email it to robert@mobilehomerepair.com ?

Thanks,
Robert

Yes, I have a diagram. I have a scanner let me scan the paper.

Ok, I sent the diagram.

Set your meter to test for 120vac. Set t-stat to call for heat and then immediately place one lead on one side of fan switch and other lead on other side of fan switch.

What does it read ?

Keep holding the leads there until you hear the click and see what it reads then.

Do this while I look at diagram.

Thanks,
Robert

The bottom showed 120v, the top showed 0v. I held the lead on and waited for the click. When it clicked the meter showed 120v on the top.

Hi,

There are two terminals on fan switch. Place one meter lead on one of those. At same time place other meter lead on other terminal.

You're testing across the fan switch, touching both terminals at sametime, one meter lead on each.

Get the reading at call for heat and hold until click and get it then.

Also, can you make a jumper wire ?

Thanks,
Robert

Ok, I'll test across the terminals and get you the results. I can make a jumper, in fact I believe that I may already have some around here.

120v before the click then 0v after the click.

Ok.

Three questions, answer carefully and detailed for me to see it from here,LOL.

When you said you had 110V going to Motor, exactly where/what were your meter leads touching to get that reading ?


Where exactly is the switch you installed or what wire did you install it into ?


How quick can you remove the switch and place system back to original ?


Got a fairly good idea, but will wait for proof first.

Take your time and answer carefully, I'll be here.

Thanks,
Robert

Ok, no jumper needed hopefully.


Can you take a precise pic of how your wires connect at connector plug ?

Do they go up inside the plug ?

If you can take the pic, send it to robert@mobilehomerepair.com again.


BTW, the fan switch is fine.


Thanks,
Robert

Picture sent. I don't know fully understand what you need. The two cut ends are for the blower. I cut them because they slide up into the connector block and I need to start the blower manually for now.

You have two wires coming directly from the motor (both black on diagram).

They come down and slide into the connector plug at the 8 and 9 holes.

Out the other side of connector block at the 8 hole is a white wire that goes to transformer.

Out the other side of 9 hole is a orange wire that goes to top terminal of fan switch.


Is all that correct ?


Did you cut the two blabk ? wires coming from motor at point where they slide into the connector plug ?

Then you straight wired a switch to those two wires going straight to motor ?

Is all this correct ?

You'll have heat still, but may not need the switch. Stay with me here.

If this don't work, you can wire switch back.

Thanks,
Robert