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To test the wiring on your four-wire gas valve in the HVAC/furnace system, start by understanding the sequence of events in the heating process. With the furnace calling for heat, check for 24V signals at the designated wires leading to the gas valve during each stage—inducer fan motor start, pressure sensor verification, and ignitor heating up.
If the gas valve is not opening and there's no "click" or initial ignition, focus on these 24V signals. Using a multimeter, measure voltage across the relevant wires. If the 24V signal is absent when it should be present, it suggests an issue with the control board. If the signal is present, the problem may lie with the gas valve itself. This process helps you identify whether the wiring or the valve is causing the malfunction in your furnace's heating sequence.
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