Honeywell T874 - Page 138

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES
60-2485—8 138
Fig. 117. Schematic and hookup of T874D with Q674L. Used in heat pump applications.
H1
FALL
L1
(HOT)
L2
R
B
2
3
4
5
6
G
Y1
Y2
W
X
L
O
ENTHALPY
CONTROL RELAY
HEAT RELAY
CONTACT 1
DEFROST
RELAY
H1 ANTICIPATOR
H2 ANTICIPATOR
C1 ANTICIPATOR
C2 ANTICIPATOR
2
2
1
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
OPTIONAL ECONOMIZER HOOKUP (DOTTED LINES).
M7755
H2
FALL
8
10
11
C1
RISE
C2
RISE
THERMOSTAT
SUBBASE
SYSTEM COMPONENTS
MOTOR
3
MOTOR
1
OUTDOOR
FAN RELAY 1
DEFROST SWITCH
RELAY
TM1 TM2
OUTDOOR
FAN RELAY 2
DEFROST
SWITCH
LOW AMBIENT
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
ENTHALPY
CONTROL
RELAY 2
ENTHALPY
CONTROL
RELAY 1
TIME DELAY
DEFROST
RELAY
HEAT
RELAY 1
OUTDOOR
THERMOSTAT
SERVICE
DEFROST
RELAY
COOL CHANGEOVER
VALVE
SYSTEM
SWITCH
OFF
COOL
HEAT
EM. HT.
LED
(GREEN)
SERVICE
LED (RED)
FAN
SWITCH
AUTO
ON
MOTOR
2