5
Wiring terminal designations
S
Input for wired
indoor or outdoor
sensors
L/A
- A
Heat Pump fault input
S O/B Changeover valve
Y
Compressor
contactor (stage 1)
AUX -
W2
Auxiliary heat relay
Heat relay (stage 2)
Y2
Compressor
contactor (stage 2)
E Emergency Heat relay
G Fan Relay W Heat relay (stage 1)
C
24 VAC common.
For 2 transformer
systems, use
common wire from
cooling transformer.
K
Connect to K on Wire
Saver Module**
U
Unused
R
24 VAC power from
heating transformer*
U Rc
24 VAC power from
cooling transformer*
Note: Not all
terminals may be
used, depending
on the system
type that is being
wired. The most
commonly used
terminals are
shaded.
* Terminal can be jumped using Slider Tab. See “Setting Slider Tabs” above.
** The THP9045A1023 Wire Saver Module can be used on heat/cool systems when
you only have four wires at the thermostat, and you need a fifth wire for a common
wire. Use the K terminal in place of the Y and G terminals on conventional or
heat pump systems to provide control of the fan and the compressor through
a single wire—the unused wire then becomes your common wire. See THP9045
instructions for more information.
Set R Slider Tab.
• Use built-in jumper (R Slider Tab)
to differentiate between one or two
transformer systems.
• If there is only one R wire, and it is
connected to the R, Rc, or RH terminal, set
the slider to the up position (1 wire).
• If there is one wire connected to the R
terminal and one wire connected to the Rc
terminal, set the slider to the down position
(2 wires).
NOTE: Slider Tabs for U terminals should be
left in place for other thermostat models.
Setting Slider Tabs
R/Rc slider tab
UWP Mounting System
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