Terminal Designations
This thermostat is shipped from the factory to operate a conventional heating
and cooling system. This thermostat may also be configured for a heat pump
system. See the “heat pump” configuration step on page 16 of this manual to
configure the thermostat for heat pump applications.
Wiring
Terminal
2 Heat 2 Cool
Conventional
System
2 Heat 1 Cool
Heat Pump
System
4 Heat 2 Cool
Heat Pump
System
RC
RH
C
B
O
G
W/E
Y
Y2
W2
Transformer power
(cooling)
Transformer power
(heating)
Transformer
common
Fan relay
First stage
of heat
First stage
of cool
Second stage
of cool
Second stage
of heat
Transformer power
(cooling)
Transformer power
(heating)
Transformer
common
Fan relay
Emergency Heat
First stage of
heat & cool
N/A
Auxiliary heat
Transformer power
(cooling)
Transformer power
(heating)
Transformer
common
Wiring
Caution:
Electrical Hazard
All components of the control
system and the thermostat
installation must conform to
Class II circuits per the NEC Code.
Warning:
Do not overtighten terminal
block screws, as this can
damage the terminal block.
A damaged terminal block
can keep the thermostat
from fitting on the subbase
correctly or cause system
operation issues.
Installation Tip
Max Torque = 6in-lbs.
Wiring
If you are replacing a thermostat,
make note of the terminal
connections on the thermostat that
is being replaced. In some cases
the wiring connections will not be
color coded. For example, the
green wire may not be connected
to the
G
terminal.
Loosen the terminal block screws.
Insert wires then retighten the
terminal block screws.
Place nonflammable insulation into
the wall opening to prevent drafts.
1.
2.
3.
Wiring Tips
C Terminal
This thermostat requires a 24V
common wire to the C terminal.
Wire Specifications
Use shielded or non-shielded 18-22
gauge thermostat wire.
Failure to disconnect the power
before beginning to install this
product can cause electrical shock
or equipment damage.
Note:
In many heat pump systems with
no emergency heat relay, a jumper
can be installed between
E
and
W2
to turn thermostat into a single
stage control for Emergency Heat
Operation.
9
10
11
12
Wiring Diagrams
Wiring Diagrams
Typical 2H/2C System: 1 Transformer
Typical 2H/2C System: 2 Transformer
Typical Heat Only System With Fan
Typical Cool-Only System With Fan
FAN RELAY
HEAT RELAY
RC
RH
Y
C
W/E
G
C
R
L2
L1
(HOT)
FAN RELAY
COMPRESSOR
RELAY
C
R
L2
L1
(HOT)
RC
RH
Y
C
G
Power supply
Factory-installed jumper. Remove only when installing on 2-transformer systems
Use either O or B terminals for changeover valve
A 24 VAC common connection is required with this thermostat.
W/E
REMOVE JUMPER
RC
RH
Y
C
W/E
G
W2
Y2
C
R
L2
L1
(HOT)
C
R
L2
L1
(HOT)
COMPRESSOR
RELAY
HEAT RELAY
FAN RELAY
RC
RH
Y
C
W/E
G
W2
Y2
COMPRESSOR
RELAY
FAN RELAY
HEAT RELAY 2
COMPRESSOR
RELAY 2
HEAT RELAY
C
R
L2
L1
(HOT)
S1/S2
Remote Sensor
Remote Sensor
Note:
In many systems with no emergency heat relay a jumper can be installed
between E and W2.
Outdoor temperature sensor, Indoor temperature sensors, and Slab sensor
wiring diagrams are located in R250S and R251S manuals.
Note:
H
Humidify
Humidify
D
Dehumidify
Dehumidify
Fan relay
Second stage of
auxiliary heat
Remote Sensor
Humidify
Dehumidify
First stage of
auxiliary heat
First stage of
heat & cool
Second stage
of heat & cool
5 Heat 3 Cool
Heat Pump
System
Transformer power
(cooling)
Transformer power
(heating)
Transformer
common
Fan relay
Second stage of
auxiliary heat
(5th stage of heat)
Remote Sensor
Humidify
Dehumidify
First stage of
auxiliary heat
(4th stage of heat)
First stage of
heat & cool
Second stage
of heat & cool
Reversing valve /
3rd stage of heat
& cool
Reversing valve /
3rd stage of heat
& cool
Reversing valve
/ configurable
terminal
Reversing valve
/ configurable
terminal
Reversing valve
/ configurable
terminal
Reversing valve
/ configurable
terminal
Reversing valve
/ configurable
terminal
Reversing valve
/ configurable
terminal
HEAT RELAY 2
COMPRESSOR
RELAY 2
Typical 2H/1C Heat Pump System
RC
RH
Y
C
W/E
G
W2
B
COMPRESSOR
RELAY
FAN RELAY
EMERGENCY
HEAT
C
R
L2
L1
(HOT)
O
COOL
CHANGEOVER
VALVE
HEAT
CHANGEOVER
VALVE
If DEHUM relay requires a normally-energized input, set Dehumidify relay to NC
in Technician Setup.
