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enclosure. This enclosure will be mounted near the blower
access panel. The dimples and knock-out are located
on the corner posts, providing ease of installation. Once
the thermostat closes, a 24 volt signal is sent to the W1
terminal instead of the Y terminal and the heating cycle will
change from Heat Pump to Gas heating. It is recommended
to set the thermostat between 35-45°F depending on
regional climate and energy rates.
Heating Cycle (Heat Pump)
The heat pump operates in the heating cycle by redirecting
refrigerant flow through the refrigerant circuit external to the
compressor. This is accomplished through the reversing
valve. Hot discharge vapor from the compressor is directed
to the indoor coil (evaporator on the cooling cycle) where
the heat is removed, and the vapor condenses to liquid.
It then goes through the expansion device to the outdoor
coil (condenser on the cooling cycle) where the liquid is
evaporated, and the vapor goes to the compressor.
When the solenoid valve coil is energizing for cooling,
the piston in the reversing valve to the low pressure (high
pressure) reverse positions in the reversing valve. In
addition to a reversing valve, a heat pump is equipped
with an expansion device for the indoor coil, and similar
equipment for the outdoor coil is provided with a defrost
control system.
Heating Cycle (Natural Gas/ LP)
1. The Dual Fuel unit will operate in gas heat mode
when the thermostat calls for a W-1 or W-2 signal. If
outdoor thermostat is installed, the unit will operate in
gas heat when ambient is below set point or the unit
receives call for low or high stage gas heat.
2. Induced draft blower energizes for 15-second pre-
purge.
3. A 7-second trial for ignition begins by energizing the
low and high stages of the gas valve along with this
spark ignition.
NOTE: The igniter produces a very intense electrical
spark that ignites the gas.
4. Main burners light and control detects presence of
flame.
5. If the call is for low stage heat, the induced draft
blower switches from high to low speed and the gas
valve from high to low stage within 5 seconds after
the main burners light. If call is for high stage heat,
induced draft blower remains at high speed and high
stage gas valve remains open.
NOTE: If a W2 is not used, the control will step to
low stage after the main burners light and remain at
low stage for 5 or 10 minutes, depending on jumper
position. If the jumper is set to none, you will never
get a call for high stage heat. If the call for HEAT
remains after the transition delay time expires, the
control will transition from low stage to high stage.
6. The 30-second HEAT FAN ON delay time begins
after the main burners light.
7. The unit delivers heat to the conditioned space until
the thermostat is satisfied.
8. Gas valve(s) de-energizes. The induced draft blower
continues operation for a 30-second post-purge.
NOTE: Induced draft blower remains at low speed (or
switches from high to low if operating at high stage
heat) for the 30-second post purge.
9. Ignition control begins timing the HEAT FAN OFF
delay. There is an adjustable HEAT FAN OFF delay
of approximately 90/120/150/180 seconds (factory
set at 150). If the unit is operating at high stage
when the call for heat is removed, the blower will
operate for 30 seconds at high heat speed then
switch to low heat speed for the remainder of the
selected HEAT FAN OFF delay.
NOTE: After the HEAT FAN OFF delay time has
elapsed, the blower will de-energize. This allows
any additional heat in the heat exchanger to be
transferred to the conditioned space.
Defrost Cycle
NOTE: The defrost board is equipped with a jumper for
SmartShift™ defrost technology operation. This operation
turns the compressor off for 30 seconds at defrost
initiation and termination. The unit is factory shipped for
SmartShift™ defrost technology operation. To operate unit
at rated efficiencies, move the jumper on the defrost board
from "DLY" to "NORM".
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30, 60
and 90 minutes may be selected by setting the circuit board
jumper to 30, 60 and 90 respectively.
Accumulation of time for the timing period selected starts
when the sensor closes (approximately 34°F), and when
the wall thermostat calls for heat. At the end of the timing
period, the unit's defrost cycle will be initiated provided the
sensor remains closed.
Upon a call for defrost, the blower will continue to run
and the defrost board will send a W1 signal to the ignition
control. At the same time the compressor will stop for 30
seconds, if the SmartShift™ defrost technology delay
feature is selected on the defrost board. At this time,
the reversing valve shifts from heat to cool position and
condenser fans shut off. The inducer motor will immediately
energize for a 15 second prepurge.
A 7-second trial for ignition begins by energizing the low
and high stages of the gas valve along with this spark
ignition. Main burners light and control detects presence
of flame. The compressor (after its 30/OFF second delay)
restarts in cooling mode to defrost the condensor coil.
When the sensor opens (approximately 60°F), the
defrost cycle is terminated and the timing period is reset.
If the defrost cycle is not terminated due to the sensor
temperature, a twelve minute override interrupts the unit's
defrost period. At this time the W1 signal is removed from
the ignition control board, the compressor will stop for a 30
second SmartShift™ defrost technology delay (if selected)
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