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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 15 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 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 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 PSIG.
DEHUMIDIFICATION – Dehumidification is
controlled through a humidistat and is independent of
the thermostat. On a call for dehumidification mode
of operation the compressor and three way valve of the
unit are energized through circuit R-F to provide
dehumidification. Dehumidification will continue
until the humidistat is satisfied.
Any time there is a call for heating mode of operation
through circuit R-W1 the dehumidification mode will
cancel and the system will return to heating operation.
Dehumidification is delay 45-60 seconds on start up
after any heating cycle is complete.
Any time the indoor coil temperature falls below 32
degrees the compressor will be de-energized until the
coil temperature rises above 57 degrees.
If the room temperature falls below 65 degrees the
dehumidification mode will discontinue until the room
temperature rises above 72 degrees.
Manual 2100-376
Page 34
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