Coleman7710-856

[Jose]

I am having problems with this furnace working correctly. At first the motor was making a very loud noise and getting very hot when it ran. I checked the motor and found it was bad. I replaced the motor and everything cycled fined for about three hours then the aux limit switch kept tripping and finally it would not reset. I replaced that along with cleaning the entire unit again like I did at the start of the season. The next day (yesterday) the fan was cycling for ten seconds then off so figured it was the fan control. I replaced that. This morning the whole unit is not working again the main burner will not ignite the only thing that runs is the booster motor and that just runs and runs. I have really no idea what to try next.

[Robert]

Check the burner and burner orifice for blockage from spider/web.

If all clear, best to call a hvac tech for specific testing.



Thanks,
Robert

[msufroggy]

Hello, I am not an HVAC expert by any means, but I had a similar problem, as my booster motor ran and ran (I have the same furnace as you). It turns out that the centrifugal switch (inside the motor) was bad. I replaced the motor (you cannot replace just the switch in this unit), and that solved the problem. It was an easy fix.
I know you said "motor" but wasn't sure what motor you replaced.

[Robert]

Check and see if the centrifugal switch is closing by testing both wires to ground for 24vac.

If closed, should have power on both wires to ground.

If not, switch is bad and booster motor will have to be replaced.


Might be other problems as well with all you stated, so an hvac tech may still be needed.


Thanks,
Robert