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A
C
IRFLOW
ONSIDERATIONS
Airflow demands are managed differently in a fully communi-
cating system than they are in a non-communicating wired sys-
tem. The system operating mode (as determined by the ther-
mostat) determines which unit calculates the system airflow
demand. If the indoor unit is responsible for determining the
airflow demand, it calculates the demand and sends it to the
ECM motor. If the outdoor unit or thermostat is responsible
for determining the demand, it calculates the demand and trans-
mits the demand along with a fan request to the indoor unit.
The indoor unit then sends the demand to the ECM motor. The
table below lists the various ComfortNet systems, the operat-
ing mode, and airflow demand source.
For example, assume the system is an air conditioner matched
with a furnace. With a call for low stage cooling, the air condi-
tioner will calculate the system's low stage cooling airflow de-
mand. The air conditioner will then send a fan request along
with the low stage cooling airflow demand to the furnace. Once
received, the furnace will send the low stage cooling airflow
demand to the ECM motor. The ECM motor then delivers the
low stage cooling airflow. See the applicable ComfortNet air
conditioner or heat pump installation manual for the airflow
delivered during cooling or heat pump heating.
In continuous fan mode, the CTK0* thermostat provides the
airflow demand. The thermostat may be configured for a low,
medium, or high continuous fan speed. The low, medium, and
high fan speeds correspond to 25%, 50%, and 75%, respectively,
of the furnaces' maximum airflow capability. During continuous fan operation, the thermostat sends a fan request along
with the continuous fan demand to the furnace. The furnace, in turn, sends the demand to the ECM motor. The ECM motor
delivers the requested continuous fan airflow.
F
F
A
OSSIL
UEL
PPLICATIONS
This furnace can be used in conjunction with a ComfortNet compatible 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 the most cost
efficient means of heating (heat pump or gas furnace). When used with the CTK0* thermostat, the furnace/heat pump system
is automatically configured as a fossil fuel system. The balance point temperature may be adjusted via the CTK0* thermo-
stat advanced user menus (see CTK0* instructions for additional information).
CTK0* W
IRING
NOTE: A removable plug connector is provided with the control to make thermostat wire connections. This plug may be removed,
wire connections made to the plug, and replaced. It is STRONGLY recommended that you do not connect multiple wires into a
single terminal. Wire nuts are recommended to ensure one 18 AWG wire is used for each terminal. Failure to do so may result
in intermittent operation.
Typical 18 AWG thermostat wire may be used to wire the system compo-
nents. One hundred (100) feet is the maximum length of wire between
indoor unit and outdoor unit, or between indoor unit and thermostat. Wire
runs over (100) feet require larger gauge wire.
F
-W
I
O
OUR
IRE
NDOOR AND
Typical ComfortNet wiring will consist of four wires between the indoor unit
and outdoor unit and between the indoor unit and thermostat. The required
wires are: (a) data lines, 1 and 2; (b) thermostat "R" (24 VAC hot) and "C"
(24 VAC common).
W
UTDOOR
IRING
System
Operating Mode
Air Conditioner +
Furnace
Continuous Fan
Heat Pump Heating
Heat Pump +
Furnace
Auxiliary Heating
Continuous Fan
Furnace + Non-
Comm 1stg Air
Conditioner
Continuous Fan
1
2
R C
1
2 R C
1 2 R C
System Wiring using Four-Wires
43
System
Airflow Dem and
Source
Cooling
Air Conditioner
Heating
Furnace
Thermostat
Cooling
Heat Pump
Heat Pump
Only
Furnace
Thermostat
Cooling
Furnace
Heating
Furnace
Thermostat
CTK0*
Thermostat
ComfortNet Compatible Furnace
Integrated Control Module
ComfortNet Compatible AC/HP
Integrated Control Module
Figure 54
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