10
60-1165—6
2. Move the system switch to AUTO or HEAT (if
used).
3. After one minute, read the ammeter and record the
reading:
Stage 1: __________ amperes.
Stage 2: __________ amperes.
NOTE: If equipment cycles too fast, set the indicator to a
higher current rating, not more than one-half division at
a time, and recheck cycle rate. Most conventional
2-stage heating equipment is designed to operate at three
cycles per hour per stage, and 1-stage heating equipment
at six cycles per hour, at 50 percent load condition.
When using the T874 Thermostat in heat pump systems,
set the heat anticipator at 140 percent of the actual
primary control current draw to reduce the cycling rate.
Most heat pump systems should cycle 2-1/2 to 3 times
per hour.
4. Hang the upper edge of the thermostat cover on top of
the thermostat base and swing the cover downward until it
engages with the cover clip.
TEMPERATURE SETTING
Move the heating and cooling set point levers (Fig. 23)
to the desired comfort positions. One lever controls all
stages of heating, and another lever controls all stages of
cooling. The minimum differential between heating and
cooling set point is 3
°
F [1.7
°
C].
Fig. 23—Location of external components.
Fig. 22—Adjustable heat anticipator scales.
SUBBASE SETTING
The subbase switching positions control the system
operation as described below (Fig. 23).
SYSTEM SWITCH (some subbases do not have all of
the following functions):
OFF: Both the heating and cooling systems are off. If
the fan switch is in AUTO position, fan is also off.
AUTO: Thermostat automatically changes between
heating and cooling system operation, depending
on the indoor temperature.
HEAT: Heating system is automatically controlled
by the thermostat. Cooling system is off.
COOL: Cooling system is automatically controlled
by the thermostat. Heating system is off.
FAN SWITCH
ON: Fan operates continuously.
AUTO: Fan operates with cooling equipment as con-
trolled by the thermostat or with the heating equip-
ment as controlled by the plenum switch.
To move the subbase switches to the desired control
positions, use thumb and index finger to slide lever. Lever
must stop over desired function indicator position for proper
circuit operation.
Checkout
HEATING
Move the system switch on the subbase to AUTO or
HEAT (if used) and the fan switch to AUTO. Move the
heating set point lever on the thermostat about 10
°
F [6
°
C]
above room temperature. Heating should start and the fan
should start after a short delay. Fan starts immediately in
heat pump systems. Move the heat lever 10
°
F [6
°
C] below
room temperature. The heating should shut off; fan should
shut off after a short delay. Fan shuts off immediately in
heat pump systems.
NOTE: In heat pump applications, time delays are involved
before the compressor is activated to prevent short cy-
cling. The delays are provided by a minimum-off timer
that prevents the compressor from starting for up to five
minutes from when the thermostat last turned off the
compressor, or from when the system first received
power.
COOLING
Move the system switch on the subbase to AUTO or
COOL (if used) and the fan switch to AUTO. Move the
cooling set point lever on the thermostat about 10
°
F [6
°
C]
below room temperature. The cooling and fan should start
(see NOTE above). Move the cool lever about 10
°
F [6
°
C]
above room temperature. The cooling and fan should stop.
FAN
Move the subbase system switch to OFF, and the fan
switch to ON. The fan should run continuously. Move the fan
switch to AUTO. In the AUTO position, fan operation is
controlled by the heating or cooling system control circuit.