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outdoor unit may send commands to or request information
from the indoor unit. This two-way digital communications be-
tween the thermostat and subsystems (indoor/outdoor unit) and
between subsystems is the key to unlocking the benefits and
features of the ComfortNet system.
Two-way digital communications is accomplished using only
two wires. The thermostat and subsystem controls are power
with 24 VAC. Thus, a maximum of 4 wires between the equip-
ment and thermostat is all that is required to operate the sys-
tem.
A
IRFLOW
C
ONSIDERATIONS
Airflow demands are managed differently in a fully communi-
cating system than they are in a non-communicating wired
system. The system operating mode (as determined by the
thermostat) determines which unit calculates the system air-
flow 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 respon-
sible for determining the demand, it calculates the demand
and transmits the demand along with a fan request to the in-
door unit. The indoor unit then sends the demand to the ECM
motor. The table below lists the various ComfortNet systems,
the operating mode, and airflow demand source.
System
System
Operating Mode
Airflow Dem and
Source
Cooling
Air Conditioner
Heating
Furnace
Continuous Fan
Thermostat
Cooling
Heat Pump
Heat Pump Heating
Only
Heat Pump
Auxiliary Heating
Furnace
Continuous Fan
Thermostat
Cooling
Furnace
Heating
Furnace
Continuous Fan
Thermostat
F Non-
Comm 1stg Air
Conditioner
Air Condi
Furnace
Heat Pump +
Furnace
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
demand. 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%, respec-
tively, of the furnaces’ maximum airflow capability. During con-
tinuous 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
OSSIL
F
UEL
A
PPLICATIONS
This furnace can be used in conjunction with a ComfortNet™ com-
patible heat pump in a fossil fuel application. A fossil fuel applica-
tion 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). The
balance point temperature may be adjusted via the CTK0* ther-
mostat advanced user menus (see CTK0* instructions for addi-
tional 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 sys-
tem components. 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
OUR
-W
IRE
I
NDOOR
AND
O
UTDOOR
W
IRING
When using the CTK01/2 ComfortNet™ wiring will consist of
four wires between the indoor unit and outdoor unit and be-
tween 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). If the outdoor unit is a communicating heat
pump, install an outdoor unit transformer and use only data 1
and data 2 wires between indoor and outdoor units.
1
2
R C
1
2
R C
CTK01/2
Thermostat
ComfortNet Compatible Furnace
Integrated Control Module
ComfortNet Compatible AC
Integrated Control Module
1
2
R C
System Wiring using Four-Wires
