THX9321/9421 P restige® IAQ and RF EIM
13 69-2490 —03
Thermostat wiring guides — Prestige THX9321

Typicalwiringofa2-heat/2-coolcon-

ventionalsystemwithonetransformer

Typicalwiringofa3-heat/2-coolheat

pumpsystemwithonetransformer

Typicalwiringforgeothermalradiant

heat,geothermalforced-airandback-

upheatwithonetransformer

Typicalwiringofa3-heat/2-coolheat

pumpsystemwithtwotransformers

1
2
3
4
5
6

U1 and U2 terminals are dry contacts.

L/A terminal sends continuous output when thermostat is set to EM HEAT mode except when set up for Economizer or TOD.

See Economizer wiring section.

U1 or U2 terminals must be used for geothermal radiant heat (ISU 2010). Thermostat allows 2 stages of radiant heat—

geothermal (stage 1) and boiler (stage 2).

"U" terminals are normally open dry contacts when set up for geothermal radiant heat. You must install a field jumper if radiant

heat is powered by system transformer. Do NOT install a field jumper if radiant heat has its own transformer.

Remove jumper if using separate transformers.

Connect the THP9045 Wiresaver Module to the K terminal in heating/cooling applications that do not have a common wire

at the thermostat. The K terminal cannot be used in heat-only applications. See THP9045 installation instructions for more

information.

CHANGEOVER VALVE
BACKUP HEAT
COMPRESSOR STAGE 1
COMPRESSOR STAGE 2
FAN RELAY
COMPRESSOR MONITOR
OR ZONE PANEL
120
VAC
O/B
AUX/E
Y
Y2
G
L/A
K
C
Rc
R
U1
U1
U2
24
VAC
Transformer
Thermostat
C
R
1
2
6MCR32948
HEAT STAGE 1
HEAT STAGE 2
COMPRESSOR STAGE 1
COMPRESSOR STAGE 2
FAN RELAY
120
VAC
W
W2
Y
Y2
G
A
K
C
Rc
R
U1
U1
U2
U2
24
VAC
Transformer
Thermostat
C
R
1
5
6
MCR32949
31
CHANGEOVER VALVE
COMPRESSOR STAGE 1
COMPRESSOR STAGE 2
FAN RELAY
COMPRESSOR MONITOR
OR ZONE PANEL
120
VAC
O/B
AUX/E
Y
Y2
G
L/A
K
C
Rc
R
U1
U1
U2
U2
24
VAC
Air Handler
Transformer
120
VAC
24
VAC
Backup Heat
Transformer
C
R
R
C
Thermostat
BACKUP HEAT
1
2
6
MCR32950
CHANGEOVER VALVE
BACKUP HEAT
COMPRESSOR STAGE 1
COMPRESSOR STAGE 2
FAN RELAY
COMPRESSOR MONITOR
OR ZONE PANEL
120
VAC
O/B
AUX/E
Y
Y2
G
L/A
K
C
Rc
R
U1
U1
U2
U2
24
VAC
Transformer
Thermostat
C
R
GEOTHERMAL
RADIANT
HEAT
STAGE 1
3
2
4
6MCR32951
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