Armstrong World Industries 203, 243, 302 Simplified Sequence HW w/UTEC 1097 Board, Refer to Figure

Service Reference Manual SEQUENCE OF OPERATIONS

2-11

Simplified Sequence - HW (w/UTEC 1097 Board)

Refer to Figure 2-2

CALL FOR HEAT

1.The indoor thermostat energizes the R-W circuit, sending a 24-volt signal to the ignition control.

2.The 24-volt signal causes the induced draft blower to start, which closes the pressure switch.

3.Once the pressure switch closes, a 30-second induced draft blower pre-purge starts.

4.After the 30-second induced draft blower pre-purge, the gas valve opens and the burners ignite. This starts a 30-second circulating air blower “on” delay.

5.The unit continues to operate in the heat mode until the indoor thermostat setting is reached. At that time, the R-W circuit is interrupted.

6.The 24-volt signal to the ignition control is inter- rupted, causing the gas valve to close and the burners to shut down.

7.A 5-second post-purge starts and following that the induced draft blower stops.

8.A 120-second circulating air blower “off” delay starts. After the elapsed time, the circulating air blower stops.

FAN ON

1.When the thermostat is switched to the “FAN ON” position, a 24-volt signal is sent to the ignition control.

2.The ignition control immediately energizes the cooling speed of the circulating air blower.

3.The circulating air blower runs in the cooling speed until the thermostat fan switch is moved back to the “AUTO” position. At this time, the circulating air blower stops.

During the call for “FAN ON”, the circulating air blower heat speed will not be energized by the ignition control unless the limit switch circuit is interrupted.

SRM-HW/HWC 2/99

Detailed Sequence follows