Older Gas Furnace Fan won't come on


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Old 11-21-11, 06:52 PM
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Older Gas Furnace Fan won't come on

Hello,

I recently bought a home that has a 30 years old furnace (my estimate). The thermostat got new batteries. My pilot light was very good (indicating gas supply is on). The blower worked okay, demonstrated by switching the thermostat fan to ON. When I switched to the HEAT mode and selected an elevated temperature, the following was what I found:

The flame arrays came on about 10 seconds after the setting. But the blower won't come on. After 30 to 60 seconds, the flames went off (probably due to over temperature).

I appreciate if you can provide some tips regarding what might be wrong about the heating system.

Hsieh
 
  #2  
Old 11-21-11, 11:29 PM
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You need to use a multimeter to check and see if the limit switch is opening and shutting off the burners. Also use the multimeter to see if 120 VAC is being switched on to power the fan motor.

Is the fan motor making noises like its trying to turn on? Is the fan hard to turn by hand?
 
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Old 11-22-11, 05:32 AM
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Hello SeattlePioneer,
Don't know if part of my background info answered one of your questions: The fan did turn on when I switched the thermostat to "Fan ON" (from "Fan AUTO").

During the heating process, I did not hear the fan motor was making an attempt to move (i.e. no noise). When I get a chance today, I'll check to see if the fan would turn freely by hand...

I thought the burner was shut of by one of the limiting switches (don't know how many there are). The big flame did come on and burn for more than 30 seconds. But the fan did not follow up, and I thought that's when the flame got shut down by the overheating switch.

Thanks for your help!

Hsieh
 

Last edited by stickshift; 11-22-11 at 09:30 AM. Reason: removed quoting of entire post
  #4  
Old 11-22-11, 09:22 AM
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Yes, having the fan turn on when switched on at the thermostat proves that it works.

Do you have a furnace with a standing pilot light, that is on even when the thermostat is not calling for heat?
 
 

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