Startup
UNT-SVX07J-EN 121
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 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
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
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 controller monitors the discharge air temperature
with a 10 kΩ thermistor. 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,” p. 120.
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