Armstrong World Industries 203, 243 Service Reference Manual, Sequence Of Operations, Flame Sense

SRM-HW/HWC 2/99

Service Reference Manual

8.When the call for heat is satisfied, the circuit be- tween R and W is interrupted, de-energizing W.

9.With W de-energized, the gas valve closes immedi- ately and the induced draft blower stops several seconds later.

10.The blower control board starts a 90-second blower “off” delay. Approximately 90 seconds later, the blower stops.

FLAME SENSE

1.During a call for heat, the spark terminal is ener- gized and the gas valve is opened to light the burners.

2.The ignition control energizes the spark terminal and the gas valve for approximately six seconds. If a flame is not sensed in this time period, the igni- tion control de-energizes the spark terminal and the gas valve. This causes the gas valve to close and the burners to shut off.

3.Since the 24-volt signal has been sent to the blower control board, the circulating air blower times on in approximately 60 seconds.

4.The induced draft blower continues to run for approximately 30 seconds, then another trial for ignition begins.

5.The ignition control runs three trials for ignition. If a flame is not sensed during these three trials, the ignition control will lockout.

6.The circulating air blower continues to run until the R-Wcircuit at the thermostat is interrupted.

7.The ignition control remains in lockout until 24-volt power to the ignition control is reset.

LIMIT OPENS

If the limit switch opens for any reason during a call for heat, the following happens:

1.If the limit switch senses that the temperature in the unit is too high, the contacts between terminals C and NC on the limit switch open and the con- tacts between C and NO close. This interrupts the 24-volt signal to the pressure switch and also de- energizes terminal P.SW on the ignition control. The gas valve closes immediately, as the 24-volt signal to terminal P.SW is no longer present. The induced draft blower and the circulating air blower continue to run. Power to blower control board terminal W is maintained. The blower continues to run until the limit switch closes or the heat call at the thermostat is satisfied.

2.When the limit switch senses that the tempera- tures in the unit are normal, the contacts between terminals C and NO open, the contacts between terminals C and NC close and the operation of the unit returns to normal.

SEQUENCE OF OPERATIONS

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PRESSURE SWITCH OPENS (BLOCKED FLUE)

1.If blockage of the flue occurs, negative pressure in the induced draft blower is reduced. At the set point of the pressure switch, the contacts open.

This interrupts the 24-volt signal to terminal P.SW on the ignition control. The gas valve closes immediately, as a relay in the ignition control opens and interrupts the signal to terminal V2 of the ignition control.

2.Terminal W on the blower control board stays energized and the circulating air blower contin- ues to run. If negative pressure is restored, the pressure switch closes and sends a 24-volt signal to the P.SW terminal on the ignition control. The ignition control makes a trial for ignition again and the operation returns to normal.

ROLLOUT SWITCH ACTIVATED

1.If conditions in the burner compartment cause the rollout switch to trip, the contacts on the switch open, interrupting the 24-volt signal going to termi- nal P.SW on the ignition control. This causes the ignition control to de-energize terminal V1, interrupting the 24-volt signal to the gas valve and immediately closing it.

2.The reason the rollout switch was tripped must be determined before any corrective action is taken.

3.The signal to terminal P.SW can only be restored if the rollout switch is reset, which can only be done manually. The W terminal on the blower control board remains energized and the circulating air blower continues to operate. Once the rollout switch is reset, the operation of the unit returns to normal.