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®
THX9321 PRESTIGE
2.0 AND THX9421 PRESTIGE
HEAT PUMP AND BACKUP HEAT OPERATION
Heat pump with outdoor temperature lockouts
Outdoor temperature lockouts are optional. See Installer Setup options (ISU 3120).
Backup heat allowed to run with heat pump
Heat pump with backup heat as needed *
*
No backup heat unless indoor temperature drops to selected Backup Heat Differential setting, or Backup Heat
Upstage Timer expires. Heat pump stays ON when backup heat turns on.
Backup heat NOT allowed to run with heat pump
*
No backup heat unless indoor temperature drops to selected Backup Heat Differential setting, or Backup
Heat Upstage Timer expires. Heat pump turns OFF when backup heat turns on.
Backup Heat Type
Electric forced air
Gas or oil forced air
Hot water radiant heat
Hot water fan coil
Other
Geothermal Radiant Heat
The thermostat can be setup to control Geothermal
Radiant Heat, Geothermal Forced Air Heat and Backup
Heat, all from one thermostat. The thermostat stages the
equipment starting with the Geothermal Radiant Heat
followed by Geothermal Forced Air Heat and then Backup
Heat as needed to maintain the desired temperature. The
thermostat allows you to set differential temperature
settings between each stage if you want the equipment to
stage a certain way (see ISU 3030 to ISU 3090, page 31).
For additional wiring diagrams, see page 144.
68-0311—07
®
Heat pump only
Backup heat only
Heat pump only
Heat pump or backup heat operates *
Backup heat only
Table 8. Heat Pump and Backup Heat Operation.
Backup Heat Operation
Allowed to run with heat pump
NOT allowed to run with heat pump
Allowed to run with heat pump
Selectable in installer setup
Selectable in installer setup
IAQ WITH EIM
(see table below)
(see table below)
NOTE: To turn off Radiant Heat during the shoulder sea-
sons, install an outdoor reset control and connect
to the Radiant Heat or switch the thermostat to
Emergency Heat mode.
Electric Backup Heat (Backup Heat
Allowed to Run with Heat Pump)
HEAT MODE
The thermostat turns on Backup Heat only when the
indoor temperature drops to the selected Backup Heat
Differential setting or the Backup Heat Upstage Timer
100
Backup heat lockout
Compressor lockout
Backup heat lockout
Compressor lockout
Backup Heat Fan Operation
Thermostat controls fan
Equipment controls fan
[n/a]
Thermostat controls fan
Selectable in installer setup
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