5
Step 4 — Final Wiring
UTILITY I/O BOARD WIRING
Bring all Utility I/O board wires together at Utility I/O
board. Make all connections as indicated in Fig. 7.
Figures 9 through 18 show the connection between the
Utility I/O board and the HVac equipment. Select proper
diagram for your equipment and connect accordingly. This
connection will require as few as 4 or as many as 7 conduc-
tors.
It is good practice to mark each wire as the final
connection is made. This will preserve its identity if it is
ever disconnected.
NOTE: Wiring diagrams appear near the end of this
document.
WIRING CONSIDERATIONS
ComfortChoice treats all furnaces as if they were 2-stage.
For single stage equipment, connect to W. The same holds
true for auxiliary heat in fan coils. With any 2-stage furnace,
configure the furnace so that low heat is controlled by W
and high heat is controlled by W and W2 together.
All 2-stage air conditioners and heat pumps need to be
configured so that Y controls low speed and Y and Y2
together control high speed in both heating and cooling.
POWER WIRING
The thermostat is powered by 24 Vac only. The
thermostat requires the 24 Vac (Rh and/or Rc and C
terminals) of the low-voltage transformer to be connected
to it for proper operation. The thermostat will not operate
without these connections. The Rh and Rc terminals are
connected via the PCB breakout jumper. For applications
using a single 24 Vac transformer for power, the breakout
jumper should remain intact. For applications using two 24
Vac transformers, the breakout jumper must be broken
because possible voltage differences between the two
transformers could cause irregular operation or damage to
the thermostat. See Figure 8. For applications using two 24
Vac transformers, one in the indoor unit and one in the
outdoor unit, connect the common wire from each to the C
terminal. Connect R from the indoor unit to the Rh terminal.
Connect R from the outdoor unit to the Rc terminal. Break
the jumper on the circuit board. See Figure 8. The W and
HUM signals are taken from the Rh power and the G signal
is taken from the Rc power. If the control has been installed
in a two-transformer application that is later changed to a
single-transformer installation, the installer must install a
field-supplied jumper between Rc and Rh. Depending on
the installation, up to 14 wires may be required. Installation
as two-piece unit is recommended. Only 2 wires are required
for connection between display module and equipment
control module. These two wires (V+ and Vg) do not
provide ordinary 24 Vac. They carry a combination of
power and communications data that is unique to these
products.
Step 5 — Understanding Sequence of Operations
TEMPERATURE SET POINTS
The ComfortChoice System uses 2 temperature set points,
the higher for cooling and the lower for heating. A minimum
difference of 2
°
F is normally enforced between heating and
cooling set points, although this value may be adjusted by
the installer. Each set point may be manually adjusted or
controlled by a programmed time schedule established by
the home owner.
The ComfortChoice thermostat can also be configured for
Heat Only or Cool Only operation. In these modes a single
set point is used to control a furnace (Heat Only) or an air
conditioner (Cool Only).
HEATING AND COOLING COMFORT SET POINTS
If space temperature is between heating and cooling set
points, then it is said to be “satisfied” with respect to
temperatures. When a space is satisfied, no heating or
cooling is required. When the space is satisfied, there is no
demand and the equipment is turned off. For example, if
cooling set point is 76°F and heating set point is 72°F,
then a space temperature of 73°F is assumed to be satisfac-
tory and no heating or cooling of the space is required.
If space temperature falls below heating set point, then that
space needs to have heat added which will raise space
temperature back to heating set point. For example, if
heating set point is 72°F and space temperature is 70°F,
then space temperature must be raised 2°F in order for the
space to be satisfied. In this case, temperature “heating
demand” for zone is 2°F (72° minus 70°F). Otherwise, if
temperature in a space rises above cooling set point, then
that space needs to have heat removed which will lower
space temperature back to cooling set point. For example, if
cooling set point is 76°F and space temperature is 77°F,
space temperature must be lowered 1°F in order for space to
be satisfied. In this case, cooling demand for space is 1°
(77°minus 76°F).
Step 6 — System Configuration
Make sure this step is not left out.
The ComfortChoice thermostat must be configured to
match the type of equipment connected to it. There are
several choices of configuration based on how the user
wants the system to operate. Configuration is done by
setting the equipment type and other options in the
thermostat on power up. Configuration options enable the
installer to configure the thermostat for a particular
installation. Most options are not presented to the home-
owner and therefore must be properly set by the installer.
Turn on power to the thermostat.
Fig. 8 - System Wiring
