HVAC Furnace Control Board - High Efficiency Furnace Control - Gas Furnace Control
This furnace control board controls much of the functions of this gas furnace with few exceptions. The main control comes from the thermostat and once the thermostat tells the gas furnace control board it is time for the heat to come on the gas furnace control board takes over from there except when the thermostat is satisfies the system shuts down. On a call for heat from the thermostat the gas furnace control board starts its sequence of operation.
The gas furnace control board enables the induced draft motor and then waits for
The pressure switch to signal that it has closed
This completes all the safety circuits as long as no limit switches are open
Once the control board has verified that all safety switches are closed it energizes the hot surface igniter or the intermittent pilot igniter
If the system is equipped with hot surface ignition a small amount of delay time is experience while the hot surface igniter heats up and then the gas valve opens and feeds gas to the main burners. If the system system is equipped with intermittent pilot the intermittent pilot valve opens on the gas valve at the same time the spark ignition begins sparking.
The gas furnace control board verifies a flame whether the system be hot surface ignition or intermittent pilot. The gas furnace control board uses flame rectification to verify the flame is lit. With an intermittent pilot system once the flame has been verified the gas furnace control board signals the main gas valve to open to feed gas to the main burners.
The main burners fire for 30 seconds to 1 minute and the gas furnace control board turns the main blower on to blow air throughout the duct work.
After the thermostat is satisfied and the space has reached desired temperature the gas furnace control board shuts down all gas to main burners and cycles the system down. The main blower fan continues to run for a few minutes to dissipate excess heat from the heat exchanger.
