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T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES
THERMOSTAT
FALL
H1 ANTICIPATOR
H1
H2
H2 ANTICIPATOR
FALL
H3 ANTICIPATOR
H3
FALL
RESET
RISE
C1
C1 ANTICIPATOR
C2 ANTICIPATOR
RISE
C2
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
2
CONNECT CHANGEOVER RELAY TO 'O' TERMINAL FOR CHANGEOVER IN COOLING OR TO 'B' TERMINAL FOR CHANGEOVER IN HEATING.
Fig. 9. T874W/Q674L for three-stage heat and two-stage cool with outdoor reset.
Mounting the Thermostat
Remove the thermostat cover by pulling the bottom
edge of the cover upward until it snaps free of the
cover clip.
NOTE: The cover is hinged at the top and must be
removed by pulling up at the bottom.
Carefully remove and discard the polystyrene
packing insert that protects the mercury switches
during shipment.
Turn over the thermostat base and note the spring
fingers that engage the subbase contacts. Make
sure the spring fingers are
proper electrical contact with the subbase.
69-0087—6
SUBBASE
1
2
3
FAN SWITCH
AUTO
4
ON
5
6
8
SYSTEM
SWITCH
EM.HT.
9
HEAT
OFF
10
COOL
11
12
not
bent flat, preventing
SYSTEM COMPONENTS
T
C815A OUTDOOR
THERMISTOR
W3
AUX. HEAT
LED (GREEN)
G
R
EM. HEAT
LED (RED)
E
X1
CHECK LED
(YELLOW)
C
CHANGEOVER
RELAY (HEAT)
B
O
X2
COMPRESSOR
CONTACTOR 1
Y1
Y2
T874Q only: Set the heat anticipator indicators to
the respective current setting for each stage. See
Setting the Heat Anticipator section. T874H and
T874W have fixed anticipation; the settings are
preselected and cannot be adjusted.
Note the tabs along the top inside edge of the
thermostat base. The tabs fit into the subbase
notches. Mount the thermostat base on the subbase
and tighten the captive mounting screws. See Fig. 1.
Place the upper edge of the thermostat cover on the
thermostat base and swing the cover downward until
it engages with the cover clip on the base.
6
AUX. HT. RELAY
FAN RELAY
EM. HT. RELAY
2
CHANGEOVER
RELAY (COOL)
COMPRESSOR
CONTACTOR 2
L1
(HOT)
L2
1
M6999
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