Installation and Maintenance Manual

Startup
UNT-SVX07D-EN 105
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
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. 104.
UNT-SVX07_-EN.book Page 105 Friday, April 27, 2012 9:40 AM