We have a modern furnace with an old thermostat that controls heat and has a wire pair traveling to the furnace's control board. I'd like to wire up a local light switch by the furnace to manually turn on the blower fan to do some extra filtration of the air in the interior of the home.
Here's the current wiring feeding down into the PCB input terminals
Could such a function be achieved by running a wire from the
G terminal through to a
light switch, followed by a second wire from the switch to one of the terminal clamps (
R) shown above? Which one would I connect to and why, and would this external wireup potentially damage or confuse the thermostat during its normal operation?
My understanding is that the
G terminal is dedicated to controlling the blower fan. Also for those modern thermostats that can manage 4 wires what are they doing exactly in terms of these terminals and the closing of certain circuits and what not? Does it essentially connect
Y or something to that effect? Does it become a conditional jumper between these terminals?