4
1H/1C System (1 transformer)
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
Y Compressor contactor
C 24VAC common [3]
W Heat
G Fan
Heat-only System
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
C 24VAC common [3]
W Heat
Series 20 Zone Valve [5]
R Series 20 valve terminal “R” [1]
Rc [R+Rc joined by Slider Tab] [2]
Y Series 20 valve terminal “W”
C 24VAC common [3]
W Series 20 valve terminal “B”
Heat-only System
(power open zone valve) [5]
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
W Valve
C 24VAC common [3]
1H/1C System (2 transformers)
R Power (heating transformer) [1]
Rc Power (cooling transformer) [1]
Y Compressor contactor
C 24VAC common [3, 4]
W Heat
G Fan
Heat-only System with Fan
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
C 24VAC common [3]
W Heat
G Fan
Cool-only System
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
Y Compressor contactor
C 24VAC common [3]
G Fan
1H/1C Heat Pump System
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
Y Compressor contactor
C 24VAC common [3]
O/B Changeover valve [6]
G Fan
W Do not use this terminal for heat
pump applications!
2H/1C Heat Pump System (PSTSN21AWH
only)
R Power [1]
Rc [R+Rc joined by Slider Tab] [2]
Y Compressor contactor
C 24VAC common [3]
O/B Changeover valve [6]
G Fan
AUX Auxiliary heat
E Emergency heat
W Do not use this terminal for heat
pump applications!
Wiring heat pump systems
Wiring conventional systems: forced air and
hydronics
NOTES
Wire specifications: Use 18- to 22-gauge thermostat wire. Shielded cable is not required.
[1] Power supply. Provide disconnect means and over-
load protection as required.
[2] Move R-Slider Tab on the base plate to the R set-
ting. For more information, see “Setting slider tabs”
on page 3
[3] Optional 24VAC common connection.
[4] Common connection must come from cooling trans-
former.
[5] In ISU set Heat system type to Radiant Heat. Set
number of cool stages to 0.
[6] In Installer Setup, set changeover valve to O (for
cool changeover) or B (for heat changeover).
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