A SERVICE OF

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IMPORTANT!
The B terminal is for
reversing valve-heat.
DO NOT connect the
B terminal to
common side of
transformer.
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.
FAN
RELAY
1ST
STAGE
HEAT
R
ONE-STAGE FURNACE
C
G
W1
Y1
1ST STAGE
COOL
120
VAC
24
VAC
1ST
STG
COOL
ONE-STAGE AIR
CONDITIONER
Y1
C
G
Y1
W1
Y2
W2
RH
RC
O
APRILAIRE MODEL
8870 THERMOSTAT
B
C
RSB
RSR
RSC
R
RSA
B+
A-
A+
B-
REF
SEE
NOTE
24V FIELD WIRING
FACTORY WIRING
OPTIONAL 24V
FIELD WIRING (SEE NOTE)
L2
L1
COMMUNICATION
TERMINALS
REMOTE
SENSOR(S)
16
DIAGRAM 1 – SINGLE STAGE FURNACE AND AC