CNT-SVX07D-EN
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Sequence of operations
Smart reset
The Tracer ZN521 will automatically restart a unit that is locked-out as a result of a Low Coil Temp
Detection (BI1) diagnostic. Referred to as “smart reset,” this automatic restart will occur 30 minutes
after the diagnostic occurs. If the unit is successfully restarted, the diagnostic is cleared. If the unit
undergoes another Low Coil Temp Detection diagnostic within a 24-hour period, the unit will be
locked out until it is manually reset. (For more information on manual resetting, see
(latching) diagnostics,” p. 48
Low-coil-temperature protection
See
“BI1: Low-coil-temperature detection,” p. 14
and “Smart reset” in the current section.
Condensate overflow
See
“BI2: Condensate overflow,” p. 14
Fan status
The fan status is based on the status of the binary output(s) dedicated to fan control. The fan status
is reported as high, medium, or low whenever the corresponding binary output is energized. The
fan status is reported as off whenever none of the fan binary outputs are energized.
Additionally, a fan-status switch can be connected to BI4 to monitor the status of the fan for belt-
driven or direct-driven units. The fan status switch provides feedback to the controller. If the fan is
not operating when the controller has the fan controlled to on, the controller will generate a Low
AirFlow—Fan Failure diagnostic.
If the 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—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 minutes
before generating another diagnostic and performing a unit shutdown.
Fan off delay
After heating has been controlled off, the Tracer ZN521 keeps the fan energized for an additional
30 seconds. The purpose of this feature is 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
Maintenance Required Timer Setpoint (configurable using the Rover service tool) is used to set the
amount of time until maintenance (typically, a filter change) is needed. If the setpoint is configured
to zero, the filter-maintenance timer is disabled.
The controller compares the fan-run time to Maintenance Required Timer Setpoint. Once the
setpoint is reached, the controller generates a Maintenance 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.
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 Rover service tool). The controller disables
freeze avoidance when the outdoor air temperature rises 3°F (1.7°C) above the Freeze Avoidance
Setpoint.
When the controller is in freeze-avoidance mode:
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