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Note: The Sequence of Operation section is in addition to the Defender Atmospheric
Service Manual, p/n 238-44943-00.
Power Up Sequence
1. Start-up: Upon power up, the gas control runs a safe start check with a typical
delay of 5 seconds.
2. Flammable Vapor Verification: The gas control verifies that the Flammable Vapor
Sensor is in the proper operating range prior to energizing any components. If the
sensor is within the proper range, the gas control resumes normal operation. If the
Flammable Vapor Sensor is out of range, the gas control LED immediately flashes
7 times with a 3 second pause.
Normal Heating Sequence
1. Thermostat Calls for Heat: Prior to energizing the relay, the gas control verifies
the safety circuit to see if it is in the correct state. If the safety circuit is closed, the
gas control LED flashes 2 times with a 3 second pause. The gas control waits 2
minutes. Then, the control cuts power to the relay. This cycle repeats until the
safety circuit opens.
2. Relay Energized
3. Safety Circuit Check: If the safety circuit does not close within 30 seconds, the
gas control LED flashes 3 times with a 3 second pause. The relay is powered for a
maximum of 30 seconds every 2 minutes trying to close the safety circuit. This
cycle repeats as long as there is a call for heat.
4. Hold Period (15 seconds)
5. Trial for Pilot Ignition (90 seconds): The gas control lights the pilot by activating
the spark igniter and gas flow to the pilot burner. If flame is not sensed within 90
seconds, the spark igniter and gas flow are deactivated. The relay will remain
powered, and the gas control LED flashes 6 times with a 3 second pause.
6. Main Burner Ignition: After pilot flame is sensed, the gas control activates the
main valve for main burner ignition. The gas control will ignore flame signals for 3
seconds to allow for the main burner to stabilize.
Sequence of Operation
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