2
MCR29436
Power options
Wiring terminal designations
Shaded areas below apply only to TH6320U/TH6220D or as otherwise noted.
Keep wires in this 
shaded  
area
Connect C for primary AC power 
(optional if batteries are installed).
Insert batteries for primary 
or backup power.
Remove factory-
installed jumper 
only for two-
transformer 
systems.
Conventional Terminals:
Rc  24VAC power from cooling 
transformer
R  24VAC power from heating 
transformer
W  Heat relay (stage 1)
W2  Heat relay (stage 2)
Y  Compressor contactor (stage 1)
Y2  Compressor contactor (stage 2)
G  Fan relay
C  24VAC common. For 2 transformer 
systems, use common wire from 
cooling transformer.
Heat Pump Terminals:
Rc  24VAC power from cooling 
transformer
R  24VAC power from heating 
transformer
O/B  Changeover valve
Y  Compressor contactor
Y2  Compressor contactor (stage 2) 
-TH6320U only
G  Fan relay
Aux/E Auxiliary/Emergency heat relay
L  Sends output when set to Em. Heat 
C  24VAC common
RcYWGRC
TH6220D
RcYWGW2Y2 RC
TH6320U
RcYWGW2Y2 RC
RcYGRC
RcY
G
C
RcYGAux
Y2
C
Aux
E