Arkansas HVACR NewsMagazine March 2025

HVACR NewsMagazine March 2025

Tech News

determine if two wires are connected, lets run some tests.

Test #1 Fan Mode

Connect one alligator clip probe to the R red wire and the other probe's alligator clip to the G green wire. The multimeter should display 0.L.

Strip the wire ends and push each appropriate wire color into the correct terminal. Have the other ends of the wires exposed out the back side of the thermostat back plate and strip the colored jacket from the end of each wire. Next, place batteries in the thermostat face. Connect the thermostat face to the wired back plate. No additional power source is needed for these tests. With this particular thermostat, R and Rc can be connected by making sure that the gray plastic tab below the R and RC terminals is pushed upward, as seen in the pic below.

Now turn the fan on using the thermostat face. The multimeter should now display 0.0Ω, signaling that R and G are now connected as seen in the pic below.

In a real life application, this means that the red 24v power wire from the furnace is now connected to the green G terminal in the thermostat, which sends 24v power to the G terminal at the furnace control board. See the pic below. The 24v power on the G terminal means that the furnace must turn the fan on.

Now that we know the terminal functions, the wire colors connected to each letter terminal, and how the multimeter can be used to