Robertshaw RS9110 Installation Manual page 12

WIRING
Terminal Designations
W Heat relay
G Fan relay
Y Compressor relay
O Heat pump reversing valve energized in cooling
RC Transformer power for cooling
RH Transformer power for heating
B Heat pump reversing valve energized in heating
C Common wire from system transformer
Notes:
RH & RC terminals
In a single-transformer system, leave the metal
jumper in place between the RH and RC. Remove
the metal jumper in two-transformer systems.
Heat pump systems
(With No Auxiliary or Emergency Heat)
If wiring to a heat pump, use a small piece of wire
(not supplied) to connect terminals W (Heat relay)
& Y (Compressor relay).
10
Common wire
The C (common wire) is optional when the
thermostat is powered by batteries.
Wire specifications
Use 18- to 22-gauge thermostat wire.
Shielded wire is not required.