Carrier 38YXA - Page 9

Fig. 16—Typical 24-v Circuit Connections using Carrier Model 2S Thermostat
with FV4A Fan Coil and Smart Staging
A97565
24 VAC HOT






R
G
W/W1
Y/Y2 Y/Y2
Y1/W2
R
DH
RVS COOLING








C
B
L
S1
S2
Y
W2
CARRIER
PROGRAMMABLE
THERMOSTAT
MODEL 2S
FV4A
FAN COIL
HEAT 
PUMP


G
O
O/W2
W2
Y1
C
W1
R
O

24 VAC COMM


HEAT STAGE 2


HEAT STAGE 3

COOL/HEAT
STAGE 1
FAN
RVS HEATING
TROUBLE
OUTDOOR
SENSOR
CONNECTION
C

J1 JUMPER


REMOVE
J2 JUMPER
FOR HEAT
STAGING
Smart Sequencing Application: Model 2S thermostat with 
switch C OFF and switch D ON uses single-speed heat pump, 
FK4 fan coil with selected 2:1 size ratio heaters. Provides 3 
stages of auxiliary heat for even heating comfort via W/W1 
and Y1/W2. Refer to FK4 Installation Instructions.
Fig. 15—Typical 24-v Circuit Connections using Carrier Model DF Thermostat with Single- or 2-Stage Furnace
A97538
G
R
Y/Y2
O/W2
CARRIER
DUAL FUEL
THERMOSTAT
MODEL DF

SINGLE-STAGE
FURNACE
HEAT PUMP
G
Y
W
C
Y
R
O
W2
Y1/W2
C
B
L
S1
S2
R
C
FURNACE

COMPRESSOR
FAN
24 VAC HOT
24 VAC COM
N/A
RVS HEATING
RVS SENSING
OUTDOOR
SENSOR
CONNECTION
OUTDOOR
TEMPERATURE
SENSOR
W/W1
See note 7
RVS COOLING
G
R
Y/Y2
O/W2
CARRIER
DUAL FUEL
THERMOSTAT
MODEL DF

TWO-STAGE OR
VARIABLE SPEED
FURNACE
HEAT PUMP
G
C
Y
R
O
W2
Y1/W2
C
B
L
S1
S2
R
C
O
W2
Y1
FURNACE LO

COMPRESSOR
FAN
24 VAC HOT
24 VAC COM
FURNACE HI
RVS HEATING
RVS SENSING
OUTDOOR
SENSOR
CONNECTION
OUTDOOR
TEMPERATURE
SENSOR
W/W1W/W1
Y/Y2
See notes 7 and 8
RVS COOLING
A97539
9