What is the first event expected to occur after the induced draft motor starts?

When the induced draft motor starts, the first event expected to occur is the closing of the pressure switch. The pressure switch is a safety device designed to ensure that the combustion process can proceed safely. It monitors the airflow generated by the induced draft motor and confirms that there is sufficient negative pressure in the combustion chamber.

Once the induced draft motor is operational, it begins to create a draft that helps vent exhaust gases outside the home. The pressure switch detects this draft, indicating that the system is venting properly. When the switch senses the correct pressure, it closes, which signals to the rest of the system that it is safe to proceed with the ignition sequence.

The closure of the pressure switch is crucial before additional components like the blower motor, ignitor, or gas valve can engage. This safety measure helps to prevent potential combustion hazards that might occur if the system is not venting properly. Thus, the correct sequence of events starts with the pressure switch closing in response to the induced draft motor's operation.