SYSTEM OPERATION
14
NOTE: Airflow will not go above the system Max CFM. If the
tonnage value selected generates an airflow value above the
Max CFM, the system will cap this value and not provide any
more airflow than the Max CFM.
R
C
G
W
Y
Dehum
Optional
Optional
INDOOR
BOARD TERMINAL
CONNECTIONS
R
C
G
W
Y
Dehum
24 VAC
Thermostat
1
2
R
C
Heat Pump
Optional
R
C
W
Y
This is the only
case where setting the
thermostat to heat pump
mode is acceptable.
Figure 39
Non-Communicating Single Stage Heat
Pump
R
C
G
W
Y
Dehum
Optional
Optional
Optional if
feature
supported by
thermostat
INDOOR
BOARD TERMINAL
CONNECTIONS
1
2
R
C
R
C
G
W
Y
Dehum
C
Y
Remote
Condensing Unit
(Single-Stage Cooling)
24 VAC
Thermostat
Figure 40
Non-Communicating Single Stage A/C
Dehumidification
The control board is equipped with a 24 volt dehum input in
the thermostat wiring connector to be used with a thermostat
or dehumidistat. Dehumidification mode allows the air
handler’s circulator blower to operate at a slightly lower speed
(85% of calculated speed) during a combined thermostat
call for cooling and thermostat call for dehumidification or
dehumidistat call for dehumidification. This lower blower
speed enhances dehumidification of the conditioned air
as it passes through the AC coil. If using the dehum input
with a thermostat, configure the thermostat to energize this
terminal when dehumidification is desired. If using an external
dehumidistat, connect it between the R and Dehum terminals.
The dehumidistat must operate on 24 VAC and utilize a switch
which
closes on humidity rise.
Refer to the low voltage wiring
diagrams for additional wiring details.
Dehumidistat (close on humidity rise)
R
C
G
Y
Dehum
Dehumidistat
(close on humidity rise)
Figure 41
Fossil Fuel Applications
This furnace can be used in conjunction with a heat pump in a
fossil fuel application. A fossil fuel application refers to a combined
gas furnace and heat pump installation which uses an outdoor
temperature sensor to determine when to run the heat pump
or gas furnace.
For non-communicating single stage heat pump installations a
fossil fuel kit can be used. Follow the wiring guidelines in the
fossil fuel kit installation instructions. All furnace connections
must be made to the furnace integrated control module and
the “FURNACE” terminal strip on the fossil fuel control board.
For Fossil Fuel systems the heat pump is given priority
when a compressor balance point lockout condition is
not present. Transitions from primary heat pump heat-
ing to backup gas heating will result in full capacity
operation during the first thermostat call. The furnace
PCB algorithms will then continuously adjust the stage
times or the percent capacity after the initial call in an
attempt to satisfy the thermostat at the target runtime.
Automatic Fossil Fuel Adjustment: If both compressor
balance point and backup heat balance point lockouts
are not present, the furnace algorithms will determine
if the heat pump is capable of satisfying the thermostat
in the selected target runtime. If the heat pump is not
capable of this it will be locked out until the furnace
can satisfy the thermostat, under the target runtime,
while running completely in low stage. At that point,
an attempt will be given to the heat pump and a deci-
sion made to keep using gas heat or to transition back
to the heat pump.
