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Two-way digital communications is accomplished using only two
wires. The thermostat and subsystem controls are powered with
24 VAC. Thus, a maximum of 4 wires between the equipment
and thermostat is all that is required to operate the system.
A
C
IRFLOW
ONSIDERATIONS
Airflow demands are managed differently in a 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 sys-
tem airflow demand. If the furnace is responsible for
determining the airflow demand, it calculates the demand
and sends it to the ECM motor. If the outdoor unit or ther-
mostat is responsible for determining the demand, it calcu-
lates the demand and transmits the demand along with a
fan request to the indoor unit. The furnace then sends the
demand to the ECM motor. The following table lists the
various ComfortNet systems, the operating mode, and air-
flow demand source.
System Operating
System
Mode
Cooling
Air Conditioner +
Heating
Furnace
Continuous Fan
Cooling
Heat Pump Heating
Only
Heat Pump +
Furnace
Auxiliary Heating
Continuous Fan
Cooling
Furnace + Non-
Comm 1stg Air
Heating
Conditioner
Continuous Fan
For example, assume the system is an air conditioner
matched with a furnace. With a call for low stage cool-
ing, the air conditioner 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 fur-
nace 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 air-
flow delivered during cooling or heat pump heating.
46
Airflow Demand Source
Air Conditioner
Furnace
Thermostat
Heat Pump
Heat Pump
Furnace
Thermostat
Furnace
Furnace
Thermostat
In continuous fan mode, the CTK0* thermostat provides
the airflow demand. The thermostat may be configured
for one of three continuous fan speed settings allow for
25%, 50% or 75% airflow, based on 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. The control board
also has the capability of providing constant fan by supply-
ing 24 VAC input to G terminal while using a communicat-
ing thermostat (CTK0*). This will allow the furnace fan to
support ERV/HRV and other accessories while using a
communicating thermostat. The continuous fan speed can
be adjusted on switch bank S5, DIP switch 3 & 4. Connec-
tion to the G terminal can be made by using two four pin
terminal blocks (similar to using a Y1 input) or by using the
9 pin connector that ships on the control board. Remove
the red keying tabs from the on-board connector block to
use either method.
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 deter-
mine the most cost efficient means of heating (heat pump or
gas furnace). The balance point temperature may be adjusted
via the CTK0* thermostat advanced user menus (see CTK0*
instructions for additional information).
CTK0* W
IRING
NOTE: Refer to Electrical Connections for 115 volt line connections
to the furnace.
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 multiple wires into a single terminal be twisted
together prior to inserting into the plug connector. Failure to do
so may result in intermittent operation.
Typical 18 AWG thermostat wire may be used to wire the system
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
-W
I
O
OUR
IRE
NDOOR AND
UTDOOR
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
IRING
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