C - A 24
TCONT900AC43UA Installer’s Guide
4 Heat/3 Cool/ Heat Pump
Communicating Programmable 3-Wire Hookup
(A/T)CONT900AC43UA Installer Guide
auxiliary heat operation and will turn off the heat pump.
During defrost, this outdoor temperature setting is ig-
nored and the defrost heater balance point outdoor
temperature thresholds are used.
There is a 5°F deadband between the Compressor
and auxiliary heat lockout temperatures.
Operation in heat mode
When the outdoor temperature is below the com-
pressor lockout temperature, only the auxiliary heat
operates. When the outdoor temperature is above
the auxiliary lockout temperature, only the compres-
sor operates (See Figure 9.)
Figure 9
When the outdoor temperature is between the two tem-
peratures, both the compressor and auxiliary heat
operate.
Defrost heater balance point control
When an outdoor temperature sensor has been dis-
covered/enabled, a separate outdoor temperature
turn-on threshold can be set for each installer heater
stage during defrost in Installer Setup numbers 0361-
0363. If the balance point for a particular heater stage
is disabled, the heater stage will be used during ev-
ery defrost cycle independent of the outdoor tem-
perature.
If the outdoor sensor is no longer reporting, all avail-
able heater stages will be used during defrost.
Table 9. Heat Pump Operation
with Lockout Temperature Set.
If the outdoor temperature sensor has not been dis-
covered/enabled, the stage or combination of stages
to be used during defrost can be set in Installer Setup
number 0364.
Operation in emergency heat mode
When the Comfort Control is placed in Emergency
Heat mode, the compressor and auxiliary lockout
features are turned off. In the Emergency Heat mode,
the compressor is locked out and only the auxiliary
heat operates. The Comfort Control is capable of
controlling up to a maximum of three Emergency
Heat stages.
Heat pump with fossil fuel heat (dual fuel) and
outdoor temperature sensor
In this operation, there is no external fossil fuel kit
(dual fuel kit) installed; the Comfort Control controls
this function. During the transition between furnace
and heat pump operation, there is a minimum Com-
fort Control time delay of 45 seconds between the
furnace turning off and the heat pump turning on and
zero seconds between the heat pump turning off and
the furnace turning on.
If the outdoor unit is missing or no longer reporting,
the control algorithm will revert back to a fossil fuel
only application.
If the heat pump fails to maintain heat while the out-
door temperature is above the auxiliary lock out tem-
perature, the furnace will be used until the setpoint is
reached, at which time heat pump operation will re-
sume.
Step 1
Choose appropriate Compressor Lockout Tempera-
ture in Installer Setup number 0350.
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