Gibson furnace blower won't stay on

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Old 12-02-14, 09:18 PM
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Question Gibson furnace blower won't stay on

I have a Gibson KG6RC 080C-12B gas furnace and a Honeywell RTH4300 thermostat in my 2900 sq ft 2-storey 10-year-old house w/full finished basement. Always had thermostat set for Auto and it worked okay. Wanted to see if setting it to On instead would help keep the second floor more comfortable. In winter it's always several degrees cooler than the main floor and in the summer at least a few degrees warmer up there. So set it to On and left it that way.

I was sitting watching TV later that night and heard the fan go off. Then a minute or two later it came back on. So when set to On, the fan is still cycling on and off. Not as much as when it's set to Auto, but I would think the On setting would truly mean, always on. Could this be a wiring issue or setting on the thermostat or furnace?
 
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Old 12-02-14, 10:15 PM
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It sounds like the blower motor may be overheating and shutting down on thermal overload. You could try running it in FAN ON mode until it fails. Turn power off to the furnace, remove the blower service door and see if the motor is extremely hot.

Also, make sure your air filter(s) is/are clean.
 
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Old 12-04-14, 06:48 PM
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Thanks, PJ for the suggestion. I thought I'd pay closer attention and can now better describe what it's doing.

When the thermostat fan switch is set to 'auto' and the thermostat calls for heat I hear a click, the furnace starts making a noise (draft inducer?) then after say 30 seconds the blower motor comes on and delivers heat. Then I set the fan to 'on' and heard the blower motor come on. Waited 30 minutes and it stayed on. The heat didn't need to come on during this time. I then increased the desired temperature and as soon as the thermostat called for heat, the blower motor shut off. Then 30 seconds later, when the blower would normally come on, it did. I repeated this a second time with the same results.

So long story short, with the fan set to 'on' the blower motor is shutting off during that initial (draft inducer?) phase. Would this be by design or could it maybe be a wiring issue or setting on the furnace?
 
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Old 12-04-14, 07:01 PM
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So long story short, with the fan set to 'on' the blower motor is shutting off during that initial (draft inducer?) phase. Would this be by design or could it maybe be a wiring issue or setting on the furnace?
I'd say by design. It sounds like the furnace is taking over the manual function with a timed/auto function.

Some unit are set up that when in FAN ON mode it runs the blower at the A/C blower speed and when the furnace runs it's at a slower speed.
 
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Old 12-04-14, 08:33 PM
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I suggest you verify the jumper that controls the fan is set to F for gas or oil systems and not to electric or heat pump. If the jumper is not set to the correct position the fan can work backwards in heating mode. A lot of times customers return thermostats to the big box stores after setting the fan control to electric.
 
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Old 01-07-15, 08:20 PM
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firedawg, I did have it set to Gas on the back of the thermostat. Fan stilling shutting off during startup of furnace. Emailed Honeywell and they suggested I switch that that to Electric so that the thermostat takes control of the fan. Same thing. So it seems this is a setting on the furnace. I have to wonder if there's a way to change this setting on the control board. Thoughts?
 
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Old 01-07-15, 08:36 PM
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In heat mode the furnace control board controls operation of the blower. The blower relay on the control board may be bad and causing the issue. If you have a voltmeter you can test for 120V at the terminals the blower leads are attached to when the blower is supposed to start up.
 
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