THX9321/9421 Prestige
®
IAQ and RF EIM
13
69-2490—05
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 radi-
ant heat, geothermal forced-air and
backup heat with one transformer. See
page 19 for operation.
Typical wiring of a 3-heat / 2-cool heat
pump system with two transformers
(example - oil forced air backup heat)
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
U2
24
VAC
Transformer
Thermostat
C
R
1
2
6
MCR32948B
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
MCR32949A
3
1
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
MCR32950A
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
6
MCR32951A
