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BAS-SVX48H-EN
page or by temporarily overriding the Reset Diagnostic Request on the Tracer TU Binary Status
page.
NNoottee:: In the ECM fan application, the ECM engine board monitors the status of the fan. In case of
a failure, the engine board disables the motor immediately, and the low airflow diagnostic
is sent.
Fan Off Delay
After heating has been controlled OFF, the UC400 Controller keeps the fan energized for an
additional 30 seconds in order to remove residual heat from the heating source.
Filter Maintenance Timer
The filter maintenance timer tracks the amount of time (in hours) that the fan is enabled. The
Filter Runtime Hours Setpoint (configured using the Tracer TU service tool) is used to set the
amount of time until maintenance (typically, a filter change) is required. The timer can be
enabled/disabled from the Supply Fan group on the Setup Parameters page in Tracer TU. The
UC400 Controller compares the fan run time to filter runtime hours setpoint. Once the setpoint is
reached, the controller generates a Filter Change Required diagnostic. When the diagnostic is
cleared, the controller resets the filter maintenance timer to zero and the timer begins
accumulating fan run time again. The diagnostics can be cleared and the filter timer reset by
temporarily overriding the Filter Timer Reset Request on the Binary Status page or by using the
reset button on the Alarms page in Tracer TU.
Freeze Avoidance
Freeze avoidance is used for low ambient temperature protection. It is initiated only when the fan
is OFF. The UC400 Controller enters the freeze avoidance mode when the outdoor air
temperature is below the freeze avoidance setpoint (configured using the Tracer TU service tool).
The controller disables freeze avoidance when the outdoor air temperature rises 3°F (1.7°C)
above the freeze avoidance setpoint. The following occurs when the controller is in freeze
avoidance mode:
• Valves are driven open to allow water to flow through the coil.
• Fan is OFF.
• Economizing is disabled.
• The outdoor/return air damper is closed.
• DX cooling is OFF.
• Electric heat stages are OFF.
Freeze Protection, Discharge Air Temperature Low Limit
The UC400 Controller monitors the discharge air temperature with a 10 kΩ thermistor wired to
AI4. The freeze protection operation is initiated whenever the discharge air temperature falls
below the discharge air temperature low limit. The discharge air temperature low limit is
configured using the Tracer TU service tool. During freeze protection, the controller increases the
heating capacity or decreases the cooling capacity in order to raise the discharge air temperature
above the low limit. If the discharge air temperature remains below the low limit for 3 minutes,
the controller generates a Discharge Air Temp Limit diagnostic.
NNoottee:: Freeze protection also performs a smart reset.
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