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FAN
RELAY
2ND
STAGE
HEAT
1ST
STAGE
HEAT
R
TWO-STAGE FURNACE
C
G
W1
Y1
W2
Y2
1ST STAGE
COOL
2ND STAGE
COOL
L1
L2
120
VAC
24
VAC
1ST
STG
COOL
2ND
STG
COOL
TWO-STAGE AIR
CONDITIONER
Y1
C
Y2
IMPORTANT!
The B terminal is for
reversing valve-heat.
DO NOT connect the
B terminal to
common side of
transformer.
G
Y1
W1
Y2
W2
RH
RC
O
APRILAIRE MODEL
8870 THERMOSTAT
COMMUNICATION
TERMINALS
B
C
RSB
RSR
RSC
R
RSA
B+
A-
A+
B-
REF
REMOTE
SENSOR(S)
NOTE: HVAC installer may need to connect
24V AC to the R and C terminals to check the
HVAC operation. If the automation system is
to be installed after the HVAC installation,
leave the R and C terminals connected to ensure
the HVAC system operates. If the automation
system is installed before the HVAC wiring,
then DO NOT connect HVAC wires to R and C.
SEE
NOTE
24V FIELD WIRING
FACTORY WIRING
OPTIONAL 24V
FIELD WIRING (SEE NOTE)
17
DIAGRAM 2 – TWO STAGE FURNACE AND TWO STAGE AC