Startup
120
UNT-SVX07E-EN
temporarily overriding the Reset Diagnostic Request on
the Tracer TU Binary Status page.
Note:
In the ECM fan application, the VelociTach 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
After heating has been controlled OFF, the 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 (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 k
Ω
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,” page 119
.
