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R= 24VAC control voltage (hot) Can be two terminals one for heat and one for cooling.
G= Fan. Switched 24vac from tstat to enable fan.
W= Heat. Switched 24VAC. Switch opens on temperature rise. Could be staged W1 W2
Y= Cool. Switched 24VAC. Switch opens on temperature drop. Could be staged Y1 Y2
O= Reversing valve for heat pump. Swithced 24VAC.
C= Common. This is the neutral side of the controls transformer.
You will see one wire from the common side of the transformer going to any component that can be considered a "load" on that transformer.
Any relay or contactor coil is a load.
Some programmable thermostats require a neutral to operate. Some will allow a small amount of current through the heat terminal to operate the thermostat but not energize the heat.
__________________
Bill K.
"I started out with nothin and I still got most of it left...."
83 911 SC Guards Red (now gone)
And I sold a bunch of parts I hadn't installed yet.
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