Armstrong World Industries 302, 243 Simplified Sequence - HW w/Fenwal 2461D Board, Call For Heat

Service Reference Manual SEQUENCE OF OPERATIONS

2-23

Simplified Sequence - HW (w/Fenwal 2461D Board)

Refer to Figure 2-4

CALL FOR HEAT

1.A call for heat closes the circuit between R and W on the thermostat. This sends a 24-volt signal to the white wire on the unit.

2.The 24-volt signal energizes terminal TH on the ignition control and the W terminal on the blower control board.

3.With the TH terminal energized, the ignition control closes an internal relay. This sends line voltage from terminal IND to the induced draft blower, starting the inducer.

4.After a pre-purge cycle of approximately 30 sec- onds, the ignition control makes a trial for ignition. Terminal V1 energizes at this time, opening the gas valve. The ignition control initiates a spark at the burner to light the main burners.

5.The trial for ignition lasts seven seconds, at which time the ignition control stops sparking. The ignition control looks at the flame sense to determine if the main burners have ignited. If flame sense is not proven, the ignition control goes through another pre-purge cycle (approximately 30 seconds) and makes another trial for ignition. It does this three times. If the three trials for ignition fail, the ignition control locks out for approximately 60 minutes. After 60 minutes, the ignition control again makes three trials for ignition. This continues as long as there is a call for heat from the thermostat.

6.When W energizes, the blower control board starts a countdown to fan “on”. Approximately 60 seconds after the thermostat initiates a call for heat, the circulating air blower starts.

7.The unit continues to operate as long as there is a call for heat from the thermostat.

8.When the heat call is satisfied, the circuit between R and W is interrupted. With the white wire de- energized, the ignition control interrupts the 24-volt signal to the gas valve. This closes the gas valve immediately and opens the internal relay that de- energizes terminal IND. The induced draft blower shut downs several seconds later.

9.The W terminal on the blower control board de- energizes. This causes the blower control board to start a countdown to blower “off”. Approximately 90 seconds later, the circulating air blower shuts down. This completes the heating cycle.

SRM-HW/HWC 2/99

Detailed Sequence follows