Honeywell T874 - Internal Schematic and Typical Hookup of a T874 R Thermostat and Q674 L Subbase in a Heat Pump Application

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES
60-2485—8 16
Fig. 17. Internal schematic and typical hookup of a T874R Thermostat and Q674L Subbase in a heat pump application.
The thermostat provides two-stage heating and one-stage cooling manual changeover operates on cooling.
M5072A
(HOT) L1
L2
1
LACO
CHP
Y
B
E
O
G
L
X
W2
W3
R
ODT 1
RTD 1 EHR 1
RTD 2
ODT 2
EHR 2 RTD 3
RD
SYSTEM
MONITOR
FAN RELAY
COMPRESSOR
CONTACTOR
COOL CHANGEOVER
VALVE
EM. HT.
RELAY
RTD 1
AUX. HT.
LED
(GREEN)
EM. HT.
LED (RED)
FAN SWITCH
ON
AUTO
SYSTEM
SWITCH
EM. HT.
HEAT
OFF
COOL
H2
FALL
H1
FALL
C1
2
3
4
5
6
H1/C1
ANTICIPATOR
H2
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
AUXILIARY HEAT LED AVAILABLE ON SOME MODELS.
THERMOSTAT
SUBBASE
SYSTEM COMPONENTS
2
2