If the main disconnect switch is open with a call for heat, how do the components behave?

If the main disconnect switch is open with a call for heat, how do the components behave?

• A. All components as though there is no call for heat.
• B. Only the heat circuit is disabled.
• C. All components are energized as though heat is being called.
• D. All components as though there is a call for heat.

Answer: (D)

When a call for heat is present, the control logic expects to energize the entire heat-demand sequence—gas valve, inducer/blower, igniter, etc.—in response to that call. If the main disconnect is open, there is no supply to actually power those components, but the control inputs still indicate a heat demand. So, from the perspective of the control state, all components are set to the heat-demand condition. In other words, they behave as though heat is being called, even though nothing will operate until power is restored. Once power is back, the system will proceed with the heat sequence based on that existing call.

When a call for heat is present, the control logic expects to energize the entire heat-demand sequence—gas valve, inducer/blower, igniter, etc.—in response to that call. If the main disconnect is open, there is no supply to actually power those components, but the control inputs still indicate a heat demand. So, from the perspective of the control state, all components are set to the heat-demand condition. In other words, they behave as though heat is being called, even though nothing will operate until power is restored. Once power is back, the system will proceed with the heat sequence based on that existing call.