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BAS-SVX065E-EN
Table 14.
Coil icing
Cooling Mode
Control Action
Economizer
None
Economizer and Stage-1 DX
Disable Stage-1 DX
Stage-1 and Stage-2 DX
Disable DX Stages 1 and 2
Note:
The fan remains ON during this operation.
Low Leaving Air Protection
This mode is activated during WSE operation and controlled by the discharge air sensor. If the
discharge air temperature drops below the AV/21 Discharge Air Temperature Low Limit Setpoint
(default 47° F) for one (1) minute, the following actions occur as shown in the following table.
This low-level diagnostic automatically resets when the binary input changes to the normal state.
The compressor minimum ON and OFF times (3 minutes) is enforced during this mode.
Table 15.
Low Leaving air
Cooling Mode
Control Action
Economizer
None
Economizer and Stage-1 DX
Disable Stage-1 DX
Stage-1 and Stage-2 DX
None
Note:
The fan remains ON during this operation.
Electric Heat Operation
The UC400 Controller supports stage-1 electric heat by three methods:
•
Supplemental
•
Boiler-less
•
Main Heat
Supplemental
When applied, the electric heat is cycled ON as the last stage of heating. Compressor 1 and 2
(where applicable) energize and the electric heat operates concurrently with the compressors, as
needed, to maintain space temperature.
Boiler-less
When applied, the electric heat enables based on the Entering Water Temperature (EWT). Both
the compressor(s) and electric heat are not allowed to operate at the same time. Boiler-less
electric heat is controlled by the EWT and compressor heat disable setpoint. If the unit is in the
heating mode and EWT falls below the compressor heat disable setpoint, the compressor is then
disabled for heating and the electric heat cycles to maintain temperature. Boiler-less control
disables if the EWT rises 5°F degrees above the compressor heat disable setpoint. The EWT value
can be either local or communicated. In applications where the local water sensor is used, the
unit may utilize the Entering Water Temperature Sampling function to verify water temperature.
Main Heat
The electric heat is utilized as the only form of heat for the unit. The compressor and electric heat
do not operate at the same time. When in the heating mode, the electric heat cycles to maintain
space temperature.
Compressor Cooling (DX)
The UC400 Controller supports two (2) stages of DX cooling. The control is proportional and
based on an error rate of 3°F degrees for single compressor operation and 5°F degrees for 2-
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