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69-0087—6
6
T874H,Q,W MULTISTAGE THERMOSTATS AND Q674B,C,G,L SUBBASES
Fig. 9. T874W/Q674L for three-stage heat and two-stage cool with outdoor reset.
1
T
W3
G
R
E
X1
C
B
O
X2
Y1
Y2
C815A OUTDOOR
THERMISTOR
AUX. HT. RELAY
FAN RELAY
EM. HT. RELAY
CHANGEOVER
RELAY (HEAT)
CHANGEOVER
RELAY (COOL)
COMPRESSOR
CONTACTOR 1
COMPRESSOR
CONTACTOR 2
EM.HT.
AUTO
ON
FAN SWITCH
H1 ANTICIPATOR
H2 ANTICIPATOR
H3 ANTICIPATOR
RESET
FALL
FALL
FALL
H1
H3
H2
AUX. HEAT
LED (GREEN)
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
CONNECT CHANGEOVER RELAY TO 'O' TERMINAL FOR CHANGEOVER IN COOLING OR TO 'B' TERMINAL FOR CHANGEOVER IN HEATING.
M6999
C1 ANTICIPATOR
RISE
RISE
C2 ANTICIPATOR
C1
C2
EM. HEAT
LED (RED)
CHECK LED
(YELLOW)
HEAT
OFF
COOL
SYSTEM
SWITCH
2
2
THERMOSTAT
SUBBASE
SYSTEM COMPONENTS
1
2
3
4
5
6
8
9
10
11
12
L1
(HOT)
L2
1
Mounting the Thermostat
³ 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
not
bent flat, preventing
proper electrical contact with the subbase.
¿ 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.
² 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.