60-1147-4 6
Fig. 9—Mounting thermostat on subbase.
THERMOSTAT
MOUNTING POST (2)
M936
50 60 70 80
50 60 70 80
HEAT COOL
THERMOSTAT
MOUNTING SLOTS (2)
SUBBASE
THERMOSTAT
CAPTIVE MOUNTING
SCREWS (2)
Settings
HEAT ANTICIPATOR SETTING
Set the adjustable heat anticipator to match the current
draw of the second stage heating primary control (Fig. 10). If
the primary control nameplate has no rating or if further
adjustment is necessary, use the following procedure to
determine the current draw of the second stage.
NOTE: The current draw of the heating stage must be measured
with the thermostat removed and the power on.
1. Connect an ac ammeter of appropriate range between
the W2 and R terminals on the subbase.
2. Move the system switch to HEAT or AUTO.
3. After one minute, read the ammeter and record the
reading.
4. After mounting the thermostat, set the adjustable heat
anticipator to match the reading measured in step 3.
Fig. 10—Stage two adjustable heat anticipator.
1.2
.4
.6
.3
.2 .15
.12
.10
.8
MOVE INDICATOR
TO MATCH CURRENT
RATING OF PRIMARY CONTROL
M3684
TEMPERATURE SETTING
Fig. 11—Location of external components (T874N
shown).
HEAT COOL
M3525
5060 70 80 50 6070 80
50 60 70 80
OFF
AUTO
FAN
HEATON AUTO
COOL AUX RELAY
HEATING
SET POINT
LEVER
COOLING
SET POINT
LEVER
THERMOMETER
(WHEN PROVIDED)
FAN
SWITCH
SYSTEM
SWITCH
OPTIONAL LED
ENUNCIATION
XXX
XXXXXXXXXXXX
XXX
XXXX
The T874N has separate heating and cooling set point
levers; the T874R has one set point lever for heating and
cooling. Move the heating and cooling set point levers (Fig.
10) to the desired comfort positions. The minimum differen-
tial between heating and cooling set point is 3° F [2° C] on the
T874N.
SUBBASE SETTING
A description of the subbase switching positions that
control the system operation follows (Fig. 11).
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, the cooling fan is also
off.
AUTO: Thermostat automatically changes between heat-
ing 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.
EM. HT.: Emergency heat relay is automatically con-
trolled by the thermostat. Cooling system is off.
FAN SWITCH
ON: Fan operates continuously.
AUTO: Fan operates automatically with heating and
cooling equipment as controlled by the thermostat.
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.