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30. SEQUENCE OF OPERATION –
HEATING
On a call for heat from the thermostat, the induced
draft blower is energized. Once sufficient draft is
established, the pressure switch contacts close and
the ignition system is energized. The direct spark
ignitor will be energized allowing gas to flow. At the
same time the main valve is energized, a 30 second
blower delay timer is activated.
After this delay, the heating speed blower relay
energizes. The blower will begin operating and
remain in operation until the set delay time after the
call for heat has been satisfied. (See Table 12 for
selectable blower off time delays.) This timing
sequence guarantees blower on, blower off operation.
This unit is equipped with a flame rollout switch
which is wired in series with the control circuit. This
is a manual reset switch and is used for the purpose of
preventing possible fire hazard in the event of a
system malfunction. If this switch has opened the
control circuit, there could be a possible system
malfunction. Some of the conditions that might cause
a rollout to occur are blockage or sooting of primary
heat exchanger, overfiring of furnace due to improper
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main burner orifices or incorrect manifold pressure,
insufficient combustion air, or installation
deficiencies with respect to return air duct design or
sizing.
Once the problem has been resolved, reset the switch
by pressing down on the reset button on top of the
switch. See Figure 16 for additional information.
31. SEQUENCE OF OPERATION –
COOLING
On a call for cooling from the room thermostat, the
high speed blower relay will be energized as well as
the compressor contactor. Following termination of
the cooling cycle, the blower motor will continue to
run for one minute.
See Figure 16 for additional information.
The unit may be equipped with a low ambient control
for lower outdoor temperature operation in the
cooling mode. If equipped with this optional control
the condenser fan will not operate immediately upon
compressor start-up, and will cycle on and off until
the condensing pressure remains above PSIG.
FIGURE 16
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Manual 2100-365
Page 29
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