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Unit protection strategies
CNT-SVX07C-EN 49
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 diag-
nostic occurs. If the unit is successfully restarted, the diagnostic is
cleared. If the unit undergoes another Low Coil Temp Detection diagnos-
tic within a 24-hour period, the unit will be locked out until it is manually
reset. (For more information on manual resetting, see “Manual (latching)
diagnostics” on page 58).
Low-coil-temperature protection
See “BI1: Low-coil-temperature detection” on page 14 and “Smart reset”
above.
Condensate overflow
See “BI2: Condensate overflow” on page 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 shut-
down 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.