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Single
Stage 1
(SS1)
Multi-
Stage 2
(MS2)
O
Energized
Constantly
in
Cool Mode
B
Energized
Constantly
in Heat, Off,
Emergency
Mode
No
Output
Cool
Mode
2nd
Stage
Cool Mode
1st Stage
Blower/
Circulator
Fan Energized
on Call for
Cool (and
Heat if
configured
for Electric
Heat)
No Output
Heat Mode
2nd Stage
Heat
Mode
1st Stage
Optional
24 Volt
(Com-
mon)
Diagnostic
Indicator
(Optional)
24 Volt
(Hot)
Cool
System
Y G W/E C L RC
CLASS II
TRANSFORMER
HOT
24VAC
NEUTRAL
120VAC
24 Volt
(Hot)
Heat
RH
120VAC
Remove Jumper Wire
between RH & RC
HOT
24VAC
NEUTRAL
CLASS II
TRANSFORMER
HEATING
COOLING
Y2 W2
Jumper
O/B
Heat Pump 1
(HP1)
Heat Pump 2
(HP2)
O
Energized in
Cool Mode
B
Energized in
Heat, Off,
Emergency
Mode
No
Output
2nd
Stage
(Com-
pressor)
Heat and
Cool Mode
1st Stage
(Compressor)
Blower/
Circulator
Fan Energized
on Call for
Heat or Cool.
Set Elect/Gas
Option for
Emergency
Mode
Heat Mode
3rd Stage.
Emergency
Mode 2nd
Stage
Heat Mode
4th Stage.
Emergency
Mode 2nd
Stage
Emergency
Mode
1st Stage
Heat Mode
2nd Stage
Heat mode
3rd Stage
Optional*
24 Volt
(Com-
mon)
Diagnostic
Indicator
or System
Malfunction
Switch
24 Volt
(Hot)
Cool
System
Y W/E C L A1 RC
CLASS II
TRANSFORMER
HOT
24VAC
NEUTRAL
120VAC
24 Volt
(Hot)
Heat
RH
Jumper
Y2 W2 G
Comfort Alert II Module
or Similar System
Diagnostic Module
See Module Instructions
for details
O/B
Energized
Pre-purge,
Morning,
Day, Eve,
Night
Single
Stage 1
(SS1)
Multi-
Stage 2
(MS2)
O
Energized Constantly
in
Cool Mode
B
Energized Constantly
in Heat, Off,
Emergency
Mode
No
Output
Cool
Mode
2nd
Stage
Cool Mode
1st Stage
Blower/
Circulator
Fan Energized
on Call for
Cool (and
Heat if
configured
for Electric
Heat)
No Output
Heat Mode
2nd Stage
Heat
Mode
1st Stage
Optional*
24 Volt
(Com-
mon)
24 Volt
(Hot)
Cool
System
Y G W/E C A1 L RC
CLASS II
TRANSFORMER
HOT
24VAC
NEUTRAL
120VAC
24 Volt
(Hot)
Heat
RH Y2 W2
Jumper
Diagnostic
Indicator
Input
or
System
Malfunction
Switch
Input
Comfort Alert II Module
or Similar System
Diagnostic Module
See Module Instructions
for details
O/B
Energized
Pre-purge,
Morning,
Day, Eve,
Night
TYPICAL WIRING 1F95-0680
Heat Pump Systems
Single Stage or Multi-Stage System (No Heat Pump) with Single Transformer
* Common connection required for diagnostic or malfunction indication.
* Common connection required for diagnostic or malfunction indication.
Single Stage or Multi-Stage System (No Heat Pump) with Two Transformers
NOTE: If continuous backlight or hardwired power input are desired but do not function in both HEAT and COOL modes, cut
the heating transformer 24V wires and tape off. Connect the neutral circuit disconnected from the heating transformer to the
neutral circuit of the cooling transformer. Disconnect the wire to the RH terminal and install a jumper between RH and RC.
Depending on the system requirements, replace the cooling transformer with a 75VA class II transformer if needed.
TYPICAL WIRING DIAGRAMS
144
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