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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 Tables 10-15 for selectable
blower off time delays.) This timing sequence
guarantees blower on, blower off operation.
This unit is equipped with a flame roll-out 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 roll-out to
occur are blockage or sooting of primary heat
exchanger, overfiring of furnace due to improper main
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Manual 2100-365Q
Page
36 of 73
SEQUENCE OF OPERATION
ELECTRONIC BLOWER CONTROL
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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 17 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 17 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 180 PSIG. LAC
energizes the fan motor at 280 PSIG, de-energizes at
180 PSIG.
FIGURE 17
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