DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > "Fan on" option on thermostat not working

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Old 06-12-2014, 12:10 AM  
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Default "Fan on" option on thermostat not working

Trying to figure out why the "on option" for fan only on thermostat is not working. We moved in this house in december, so we only used the heating so far. The house is quad with 2 furnaces and 2 ac units. Since is not hot enough for ac i just tried to use the fan only option, so i put the heat and ac on off. One fan works, one doesn't, but the ac works on both units. We checked the wires on the wall, for the thermostat, they are all conected. Any sugestions? By the way, my hubby turned the pilot light off, for both furnaces, i don't know if it has anything to do with that.

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Old 06-12-2014, 05:42 AM  
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Set the thermostat well above or below the current temp using either heat or cool mode. Then try the "ON" for the thermostat. If this doesn't work then it might be that they didn't wire in the fan.
I can tell you more if you can answer the following:

How many wires are attached to the back of the thermostat(3,4,5)?
What colors are the wired attached to the back of the thermostat (red, green, white, yellow, black)?
What terminals are they attached on the back of the thermostat (R,C,Y,W,Y1,W2,G, etc...)?
Same information as above but, this time we want to look inside the air handler where the thermostat wires connect.

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Old 06-12-2014, 08:15 AM  
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There are 4 wires, white, blue, green and red, all conected.
White conected at W, blue conected at Y, green conected at G, and red at R.
Was the blue suppose to be conected at B?
I cannot try the fan with the heat, since the furnace is off, pilot is off too. But it seems the fan works with the ac. But if i put the thermostat on off and put the fan on, nothing happens.
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Old 06-12-2014, 11:25 AM  
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Almost certainly you'll need a multimeter and a schematic. And sometimes the stat wires change colors inside the wall.

To test the stat independently of the system you'll need a 24 vac transformer and load [like a resistor from Radio Shack]. The stat is just switches controlled by temperature and the user's wishes.

If you just screw around with the wires you could damage something but you may not know it.
This is more confusing than house wiring but mistakes with these systems don't usually cause globs of molten copper to become airborne.

Last edited by Wuzzat?; 06-12-2014 at 04:42 PM.
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