Coleman 8400-815 Furnace Blower Motor Won't Come On

[DavidW]

The blower motor will not come on automatically.

The heating elements fire up and glow until the limit switches turn them off.

I replaced the sequencers today, but still no blower.

The tran former appears to be working: outputs 24 VAC.

When the blower switch is toggled to manual, the blower fan comes on fine.

The blower motor runs very well and is quiet.

Sometimes, when on auto, the heating elements go thru several cycles and the blower starts working like its suppose to.

But most of the time now it doesn't.

The thermostat is about 18 mos. old (Hunter programable). The blower motor was replaced about (12) years ago.

There are more wires running to the motor than what the schematic shows.

Any suggestions?

[DavidW]

I by-passed the toggle switch by running a jumper wire from the gray wire coming off of the sequencer to the blue wire going to the blower motor.

The blower still will not operate automatically.

I checked for voltage at the jumper. The tester indicator light came on, but the blower didn't (??)

Yet, I hook the toggle switch back up and switch it to manual and the blower comes on fine. This is strange.

[Robert]

Hi,

Trace the wires from blower that is used for heat speed down to connector plug, probably a molex connector plug.

Unplug and then set t-stat to auto and heat and set for a call for heat.

After 30 secs test where the speed wire and common wire would connect and see if there is 240VAC there.

If not, test each to a good ground and see if you get 120VAC.


For A/C and fan manual ON, the blower runs at high speed.

For heat, it runs at low or med. low.

So, could be that there is a loose connection at the plug or at any other connection along the way.



Thanks,
Robert

[DavidW]

Robert,

Problem solved.

With your instructions, I located a bad connector on the yellow 10 ga. wire running from the heating element to M6 on the sequencer.

I now realise no votage was being supplied to the blower on automatic, because the power comes from a heating element connection, thru M6, outputting to M5 and then to the fan motor.

The motor circuit was not closing due to a bad connector.

It is now working just fine.

Thanks for the website. Thank you for sharing your knowledge.

[Robert]

Hi David,

You're very welcome. Please be sure your wiring diagram shows the sequencer to be wired as you stated.

It may, but I have never seen one like that in 28+ years.


Normally, the blower is wired as you stated, but through M1 and M2.


The elements should come on M1/M2, then M3/M4 and last M5/M6.


Then go off in reverse, M5/M6, then M3/M4 and last M1/M2.


Blower remains on until cooled to design temp.


Just want you to be safe and continue to have good furnace operations.


Thanks.


Take care and best wishes,
Robert

[DavidW]

I have made a couple of errors in reporting this problem.

The furnace is a 3400-815, not 8400-815.

And you are correct, M6 outputs to a 60 amp fuse, not the blower motor.

At any rate, the system is working fine again.

Thank you again for your help.

In (15) years, the furnace has needed only three things:

1. Change the filter regularly.
2. Replaced the blower motor (12) years ago.
3. Installed a new programmable thermostat.

Very reliable.

[Robert]

Hi David,

Yes sir, they are very reliable. They cost more or used to cost more to operate anyway, but not being too much to them, are more reliable.


I had already gotten the 8400/3400, there isn't an 8400.


Glad it is all ok and fine now and you're enjoying the heat.


Thanks for updates and corrections.



Glad we could assist and you're very welcome.



Take care and best wishes,
Robert

[DavidW]

Robert,

This Coleman furnace is not too bad.

The highest winter electric bill (includes well, refrig, w/d, lights, etc.) was $175.00 for one month. That was before the roof-over.

Had an aluminum roof-over with 2" of foam/refrigeration type insulation installed two years ago. My latest Duke Energy bill was $73.00 (last of Dec. and most of Jan.).

Summer with the a/c window units costs about $50.00 per month. That includes everything.

This is not too bad for a 14' X 70'.

Between the roof-over and a programmable thermostat, the electric bill has gone down.

[Robert]

Nope, not too shabby, LOL.


I'd keep her for sure with those bills.



Take care and best wishes,
Robert