HVAC Site - Professional HVAC Contractors Forum banner

Thermostat fan

145 Views 3 Replies 3 Participants Last post by  eggs
We have a gas furnace that was tuned up last fall and a new thermostat installed. We like to have our fan running constantly, which it did all winter. Now that we have the AC on, the fan is not running continuously. I've done my research and know that for the fan to run continously, the fan should be put to the on postion. Here is where my issue lies. With the heat on, the fan runs continously with the fan in the auto position, which is NOT correct. When the ac is on, the fan will NOT run continously in either the on or auto position. I then took the thermostat cover off and noticed that the green wire is not attached at all, hard to see in the picture, but there is a green wire way back in there. One, how was the fan even running with this NOT connected? Two, how do I fix this so the fan will work correctly in the on and auto positions. I took the cover off the furnace and verified that all wires, including the green are connected at the furnace. Is the wiring in the picture connected correctly at the thermostat and do I need to just connect the green wire at the thermostat?


See less See more
1 - 1 of 4 Posts
He said it well. Be careful whom you hire to work on your furnace. So many hacks out there. I assume your furnace is not a heat pump, if it is, things are different. Not rocket science here - Red wire to R, Yellow Wire to Y, White wire to W, Green to G. To help you understand what all that means.
Red (R) is 24 volts AC - powers up the items in your furnace.
White (W) is heat. On a call for heat, R connects to W and starts the heating cycle, also the furnace will bring the fan on when it is ready.
Yellow (Y) is AC, It should also bring the fan on and sends 24 volts AC to the AC outside
Green (G) turns the fan on to high speed. When you turn the Auo fan to ON, this powers up - turns fan on
B terminal - wire color can vary - It is for a heat pump - A heat pump runs an AC backwards, blows heat inside and the cold air outside.

Markusolas states the rest very clearly - Good Luck
1 - 1 of 4 Posts