Trane HUV Installation, Operation And Maintenance Manual page 84

Startup
• If the fan is not operating when the controller has the
fan controlled to ON, the controller generates a Low
Airflow-Supply Fan Failure diagnostic.
• If the UC400 controller energizes the fan output for
1 minute, and the fan status switch indicates no fan
operation, the controller performs a unit shutdown
and generates a Low Airflow-Supply Fan Failure
diagnostic.
• If the fan has been operating normally for one minute,
but the fan status switch indicates no fan operation, the
same diagnostic is generated.
This manual diagnostic discontinues unit operation until
the diagnostic has been cleared from the controller. If a
diagnostic reset is sent to the controller, and the fan
condition still exists, the controller attempts to run the fan
for 1 minute before generating another diagnostic and
performing a unit shutdown. A diagnostic reset can be
sent to the controller from the Tracer TU Alarms page or by
temporarily overriding the Reset Diagnostic Request on
the Tracer TU Binary Status page.
Note: In the ECM fan application, the ECM engine board
will monitor the status of the fan. In case of a
failure, the engine board will disable the motor
immediately, and the low airflow diagnostic is sent.
Fan Off Delay (UC400)
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 (UC400)
The filter maintenance timer tracks the amount of time (in
hours) that the fan is enabled. The Filter Runtime Hours
Setpoint (configurable 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 (UC400)
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 (configurable using the Tracer TU service tool).
The controller disables freeze avoidance when the outdoor
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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) (UC400)
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 configurable 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.
Freeze protection will also perform a smart reset. Refer to
"Smart Reset (UC400), " p. 83.
UV-SVN02C-EN