Arkansas HVACR NewsMagazine March 2025

HVACR NewsMagazine March 2025

Tech News

Next, touch the two multimeter probes together. The measurement should be 0.0Ω or very close to this measurement as shown in the pic below. If the measurement is .1Ω or higher, turn the multimeter off in order to clean the probes with non-soaped steel wool. After cleaning, turn the multimeter back on again and touch the probes together. If you don't measure 0.0Ω, you may want to replace the multimeter leads with new ones that are not stretched and have a high resistance value.

Thermostat Wiring

We can use this knowledge to visually determine which thermostat wires connect together inside the thermostat when calling for fan, heat, or air conditioning mode to turn on. Instead of connecting the thermostat wire from the thermostat to a HVAC system, we can simply cut a 6" length of thermostat wire, strip the wire ends, connect these wires to the appropriate terminals and have the other ends of the wires exposed out of the back of the thermostat. The batteries in the thermostat will allow the thermostat to electronically switch between the different modes when manually set by the user, in order to to connect the appropriate wires together. We can monitor which wires are connected by attaching the multimeter leads to the individual, exposed thermostat wires with alligator clips. What we need to know now is the thermostat color code and appropriate terminal functions. These are as follows:

Anyway, 0.0Ω means that the circuit is closed and fully connected between the two probes. View the pic below for two connected wires between the two probes.

R= red, 24v power, control wire for heat

Rc=red, 24v power, control wire for fan and cooling

C= blue, 24v common wire

G= green, fan

W= white, heat

Y= yellow, cooling

Below is a thermostat wiring diagram for a furnace and air conditioner. Utilize this pic to connect the wires to the thermostat back plate terminals.