What must be verified before replacing the electronic control board if the onboard diagnostics fault is incorrect?

Before replacing the electronic control board, it's essential to verify the power supply and connections because issues related to power can lead to faulty diagnostics in HVAC systems. If there are problems such as loose or corroded connections, insufficient power supply, or fluctuations in voltage, these can trigger erroneous codes from the onboard diagnostic system. This means that what appears to be a problem with the control board may actually stem from issues with the electrical supply to the system.

By confirming that the power supply is stable and all connections are secure, you can rule out electrical issues as the cause of incorrect diagnostics. Only after establishing that the power supply is reliable should one consider replacing the control board, ensuring that any investment in parts is justified by addressing the root cause of the issue. Verifying other components, while important, does not directly address the potential for power-related issues that can lead to misleading diagnostic fault indications.