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T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES
139 60-2485—8
Fig. 118. Schematic and hookup of T874W with Q674L. Used in heat pump applications.
H1
FALL
H2
FALL
L1
(HOT)
L2
R
B
2
1
3
4
5
6
G
Y1
Y2
O
X
E
A
ECONOMIZER
RELAY
HEAT RELAY
CONTACT 1
DEFROST
RELAY
H2 ANTICIPATOR
H1
ANTICIPATOR
H3
ANTICIPATOR
C2 ANTICIPATOR
C1 ANTICIPATOR
RESET HEATER
2
2
1
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
OPTIONAL ECONOMIZER HOOKUP (DOTTED LINES).
M7756
H3
FALL
8
9
10
11
12
C1
RISE
C2
RISE
THERMOSTAT
SUBBASE
SYSTEM COMPONENTS
MOTOR
3
MOTOR
1
MOTOR
2
OUTDOOR
FAN RELAY 1
DEFROST SWITCH
RELAY
DEFROST
RELAY
TM1 TM2
OUTDOOR
FAN RELAY 2
DEFROST
SWITCH
OUTDOOR
THERMOSTAT 1
OUTDOOR
FAN RELAY 3
1ST STAGE
SHORT
CYCLE
CONTROL
2ND STAGE
SHORT
CYCLE
CONTROL
1ST STAGE LOW
PRESSURE LIMIT
2ND STAGE LOW
PRESSURE LIMIT
TIME DELAY
HEATER
ECONOMIZER
RELAY
ENTHALPY
CONTROL
ECONO-
MIZER
RELAY 2
ECONOMISER
RELAY 1
TIME DELAY
RELAY
DEFROST
RELAY
COOL CHANGEOVER
VALVE
EMERGENCY
HEAT RELAY
W
AUXILIARY
HEAT RELAY
SYSTEM
SWITCH
OFF
COOL
HEAT
EM. HT.
AUX. HEAT
LED (GREEN)
EM. HEAT
LED (RED)
FAN
SWITCH
AUTO
ON
DEFROST
RELAY
CONTACT
DEFROST
RELAY
CONTACT
C815 OUTDOOR
THERMISTOR