Thermo Products MDA1-100N, MDA1-50N, MHA1-75N, MHA1-100N Mode of Operation Control System Action

All installations and services must be performed by qualified service personnel.

Mode of Operation Control System Action

Main Burner

Operation

Repeated Trials for Ignition.

Call for Heat

Satisfied

System Lockout

After delay-to-fan-on period ends, circulating air fan is energized at heating speed. The (optional) electronic air cleaner and humidifier are energized.

When thermostat is satisfied, contacts open and the gas valve is de-energized. After proof of flame loss, inducer and (optional) humidifier are de-energized. The delay-to-fan-off period begins (180 seconds)

If ignition attempt is unsuccessful, one more retry will be made before the ignition control module goes into system lockout.

If flame is detected,then lost, the ignition control module will repeat the initial ignition sequence for a total of four recycles. After four unsuccessful recycle attempts, the control will go into system lockout. The ignition control module will reset automatically in 60 minutes.

If system is in lockout, try to reset by interrupting the power

to the furnace at the disconnecting switch or interrupting the call for heat at the thermostat. If this does

not restart the system, refer to the troubleshooting section of this manual.

End of Cycle	After the delay-to-fan-off
	period ends, the circulating
	air fan and {optional)
	electronic air cleaner are
	de-energized.

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