When measuring across the transformer secondary, what would indicate a need to test R-C if showing 24 volts?

When measuring across the transformer secondary and observing 24 volts, seeing 0 volts on the W-C side indicates a need to test the R-C circuit. The W-C designation typically refers to the connection points for the heating circuit, and 0 volts suggests that there is no potential difference, meaning that the control circuit is not functioning as expected.

In a properly functioning system, you would still expect to see some voltage on the W-C side if the thermostat is calling for heat or the system is active. The presence of a solid 24 volts on the transformer’s secondary implies that the transformer itself is functioning and supplying the correct voltage. However, if the W-C measurement shows 0 volts, this indicates a possible issue either with the thermostat, wiring, or components connected to W-C. It can be a sign of a broken circuit or a failure in the control mechanism, prompting further investigation into the R-C connections or components.

This troubleshooting step is critical as it helps narrow down where the fault may lie in the HVAC system's operation. By focusing on this specific measurement, technicians can better isolate issues in either the thermostat or wiring, ensuring efficient and accurate repairs.