# "Fan on" option on thermostat not working



## Emac (Jun 12, 2014)

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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## kok328 (Jun 12, 2014)

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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## Emac (Jun 12, 2014)

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.
Thank you


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## Wuzzat? (Jun 12, 2014)

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.


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## Emac (Oct 8, 2015)

Why is the fan working with the AC but not by itself, or "on" option?


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## WyrTwister (Oct 11, 2015)

Look at the furnace & find those thermostat wires .  You should also have small wires from the furnace to the condenser unit , outside .

     Look to see if all is well , there .  All the wires securely connected to their respective terminals / or wires .

     This will be much simpler if you have a volt - ohm meter ( multi-meter ) .  You can get one at Home Depot / Harbor Freight , that will do for this , for around $ 10 .

God bless
Wyr


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## slownsteady (Oct 11, 2015)

Always check the simple answer first. Does the Tstat have batteries? Are they fresh?


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## WyrTwister (Oct 12, 2015)

I think the OP said there are 4 wires to the tstat .  Works OK for a mercury bulb tstat .  

     You are right , an electronic tstat would need batteries , since no common wire .

     I guess I figured , batteries , if present , would have been replaced before the OP got on the internet ?

     Yea , I know ......

God bless
Wyr


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## Emac (Oct 13, 2015)

I'll ask my husband to look at all the answers, thank you. 
What i can tell you so far is that the problem is not the tstat. We have 2 furnaces, so we moved the tstat from furnace1 to furnace2, and it works fine and we put a Nest at furnace1, and we got the same problem. 
So, the problem is at unit 1, the fan works with the furnace or AC, but if i want to use it by itself to just circulate the air, i got nothing.


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## WyrTwister (Oct 14, 2015)

My guess is the problem is with the green wire , from the tstat to the furnace .

     You can verify that by putting the tstat to fan - on and measuring from the green at the furnace to common .

God bless
Wyr


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