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Service Reference Manual SEQUENCE OF OPERATIONS
2-33
SRM-HW/HWC 2/99
Simplified Sequence - HW (w/Fenwal 05-29 Board)
Refer to Figure 2-6
CALL FOR HEAT
1. The indoor thermostat calls for heat by energizing
the R-W circuit.
2. This sends a 24-volt signal to the ignition control,
causing the induced draft blower to run.
3. A 24-volt signal is also sent to the blower control
board at this time, starting a 60-second circulating
air blower “on” delay. The circulating air blower
starts 60 seconds after the initial call for heat.
4. The induced draft blower causes the pressure
switch to close which starts a 30-second pre-purge.
After the pre-purge period, the burners ignite.
5. The unit operates in the heating mode until the
indoor thermostat setting is reached and the R-W
circuit is interrupted.
6. When the R-W circuit is interrupted, the 24-volt
signal to the ignition control and the signal to the
blower control board are interrupted.
7. The induced draft blower stops within several
seconds and a 90-second circulating air blower “off”
delay starts. Following the delay period, the circu-
lating air blower shuts off.
Detailed Sequence follows