Defrost Operation
A unique feature of this thermostat is that a defrost cycle, once
started, will always be completed. This is true even if thermostat is
satisfied during defrost. The result is that a heating cycle never
begins with an uncompleted defrost and its associated "cold blow".
During operation of HP in heating mode, HP itself determines
when a defrost is necessary. It initiates defrost by energizing its O
and W wires. The signal on the O wire switches HP from heating
to cooling mode and W signal starts furnace. Thermostat monitors
this action by sensing the signal (which it did not create) on the O
line. It responds by turning on its W outputs (both if 2-stage
furnace) to hold furnace on high heat. At completion of defrost,
indicated by removal of signal from HP on O wire, thermostat does
1 of 2 things. If it is satisfied, it turns off all Y, G, and W outputs
which results in all equipment off. If not satisfied, it will turn off
Y and G, leaving W on until it becomes satisfied. In this way it
assures that furnace will be used to satisfy a heat demand existing
after a defrost cycle is completed.
Emergency Heat
If EHEAT mode is selected at thermostat, all heating will be done
by furnace.
Continuous Fan
If FAN ON is selected, thermostat energizes G terminal, which
causes fan to operate when both heating and cooling are off.
Staging Sequence—Heating
Depending on whether HP is single or 2 speed and whether furnace
is single or 2 stage, the staging of thermostat outputs with
increasing demand varies. Table 1 shows the heating staging
sequence for all 4 possible combinations of single- and multi-stage
equipment. Note that thermostat itself has a maximum of 3 heating
stages. Note also that at outdoor temperatures below selected
balance point setting no HP operation is allowed. As discussed
earlier, once furnace is turned on, it remains on to satisfy all
demand.
A "freeze protect" feature is built into the dual fuel thermostat. If
indoor temperature sensor fails, and thermostat is in HEAT or
AUTO mode, heat will be cycled when outdoor temperature is
below 50°F. The amount of heat supplied will increase as outdoor
temperature decreases, keeping structure from freezing.
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INSTALLATION CONSIDERATIONS
POWER
Note that this control does not require batteries and is not "power
stealing". It does require 24 vac (R and C terminals) of the
low-voltage transformer to be connected to it for proper operation.
It will not operate without these 2 connections.
OUTDOOR TEMPERATURE SENSING
The dual fuel thermostat uses outdoor temperature to determine
whether the furnace or the heat pump is allowed to operate. The
outdoor temperature sensor, Part No. TSTATXXSEN01-B, is
supplied with the unit and must be installed. Plan installation so
that 2 wires can be run from the thermostat to an outdoor location,
preferably on the north side of the house or refer to Installation
Instructions included with the outdoor temperature sensor for
simplified connection. Sensor can be mounted to outdoor unit and
existing control wires may be used for its connection. Details are
provided in the sensor Installation Instructions.
INSTALLATION
Step 1—Thermostat Location
Thermostat should be mounted:
•
Approximately 5 ft (1.5m) from floor.
•
Close to or in a frequently used room, preferably on an inside
partitioning wall.
•
On a section of wall without pipes or duct work.
•
In a location where the outdoor temperature sensor wires can be
routed to thermostat location. It is acceptable to use 2 separate
wires in thermostat cable to connect outdoor sensor. These
wires may be connected at furnace to another pair continuing to
outdoor heat pump. The outdoor sensor may then be mounted
and connected in vicinity of heat pump, but be sure it is not
located in direct sunlight.
Thermostat should NOT be mounted:
•
Close to a window, on an outside wall, or next to a door leading
to the outside.
•
Exposed to direct light and heat from a lamp, sun, fireplace, or
other temperature-radiating object which may cause a false
reading.
•
Close to or in direct airflow from supply registers and return-air
grilles.
•
In areas with poor air circulation, such as behind a door or in
an alcove.
Step 2—Set DIP Switches
There is a 4 section DIP switch within the thermostat which must
be properly set by the installer. It is easiest to set these 4 switches
before the thermostat is mounted on the wall, so STOP and
complete the following steps:
1. Open hinged thermostat cover.
2. Remove cover completely by snapping it apart at hinge.
3. Open thermostat by pressing back half of the right end of
plastic case inward while, at the same time, pulling front and
back halves apart at the right end. The 2 halves will swing
apart.
4. Snap hinge apart to completely separate the 2 halves.
5. Switches are located in upper right corner of circuit board. to
change switch position, use corner of a small screwdriver to
slide switch to opposite position.
6. After switches have been set, do not reassemble the 2 halves.
The rear plastic will be first mounted to wall.
Switch A - Not Used in Dual Fuel Thermostats
This switch must be in OFF position in all dual fuel applications.
DO NOT turn ON.
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Table 1—Heating Stages
WIRING DIAGRAM
SYSTEM TYPE
BALANCE POINT
SETTING
STAGE 1
STAGE 2
STAGE 3
Fig. 2
1-speed HP
1-stage furnace
Above
HP
Furnace
—
Below
Furnace
—
—
Fig. 4, 6, 8
1-speed HP
2-stage furnace
Above
HP
Furnace Lo
Furnace Hi
Below
Furnace Lo
Furnace Hi
—
Fig. 3
2-speed HP
1-stage furnace
Above
HP Lo
HP Hi
Furnace
Below
Furnace
—
—
Fig. 5, 7, 9
2-speed HP
2-stage furnace
Above
HP Lo
HP Hi
Furnace Lo or Hi
Below
Furnace Lo or Hi
—
—
3
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