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UV-SVP01A-EN 45
Unit Operation
than or equal to the configurable
exhaust enable setpoint. This is
useful for exhaust fans designed
to offset the added economizer
ventilation.
The exhaust fan is disabled when
the outdoor air damper position
drops 10% below the exhaust en-
able point. If the exhaust fan en-
able setpoint is less than 10%, the
Tracer ZN.520 controller energizes
the exhaust fan at the enable point
and disables it when the outdoor
air damper closes.
Output Overrides
Manual Output Test
Manual output test allows the bi-
nary outputs to be energized in a
predefined sequence.(For more in-
formation see, Manual Output
Test, on page 48 for more informa-
tion.)
Water Valve Override
To enable quicker water balanc-
ing, the controller allows a user to
specify the desired state of all wa-
ter valves. The values supported
are:
q Open all valves
q Close all valves
The valves in the system will re-
main open for two hours or until
normal operation is resumed.
The Tracer Summit or the Rover
service tool is required to access
this feature.
Fan Status
There are two ways to do fan sta-
tus monitoring:
1. The status of the fan is
reported based on the state of
the binary output(s) dedicated
to fan control. The fan status
is reported as HIGH or LOW
whenever the corresponding
binary output is directed ON.
The fan status is reported as
OFF when none of the fan out-
puts are directed ON.
2. The Tracer ZN.520 controller
has a binary input available
for a fan status device (current
sensing relay or differential
pressure switch) which can
provide feedback of fan opera-
tion. If the device does not
indicate fan operation after 1
minute, a unit shutdown is ini-
tiated, and the unit is latched
OFF.
Filter Status/
Maintenance Timer
The unit filter status\maintenance
timer is based on the cumulative
run hours of the unit fan. The con-
troller compares the fan run time
against an adjustable fan run hour
limit and recommends unit main-
tenance as required.
The Rover service tool is used to
edit the maintenance required set-
point time. Once the setpoint limit
is exceeded, the controller gener-
ates a MAINTENANCE REQUIRED infor-
mational diagnostic. When the
maintenance required setpoint
time is set to zero, the controller
disables this feature.
You can use the Trace Summit or
the Rover service tool to clear the
MAINTENANCE REQUIRED informa-
tional diagnostic. Once the diag-
nostic is cleared, the controller
resets the fan run time to zero and
begins accumulating fan run
hours again.
Note: If at any time the unit
loses power, the timer is reset
to zero.
Other Modes
DEHUMIDIFICATION
Note: If the unit is in the
unoccupied mode, the
dehumidification routine will
not operate
Dehumidification is possible when
mechanical cooling is available;
the heating capacity is in the re-
heat position; and the space rela-
tive humidity setpoint is valid.
The controller starts dehumidify-
ing the space when the space hu-
midity exceeds the humidity
setpoint. The controller continues
to dehumidify until the sensed hu-
midity falls below the setpoint mi-
nus the relative humidity offset.
The controller uses the cooling
and reheat coils simultaneously to
dehumidify the space. When de-
humidifying, the discharge air
temperature is controlled to main-
tain the space temperature at the
current setpoint.
Economizing is disabled during
the dehumidification mode.
Note: While in the
dehumidification mode, if
there is a call for capacity by
the unit, the zone temperature
setpoint will take priority over
the relative humidity
setpoints.
DEFROST
For defrost operation, a sensor is
wired in series with the DX cooling
relay. When a defrost condition is
detected, the condensing unit is
disabled, and the unit is placed in
the DEFROST mode.
During DEFROST the condensing
unit is OFF the outside air damper
is set to the minimum positions,
and the fan will continue to oper-
ate as continuous. The unit will re-
main in the DEFROST mode until
the senor resets at 48°F. The unit
will return to NORMAL operation af-
ter the mode is discontinued.
FREEZE AVOIDANCE
FREEZE AVOIDANCE is used as low
ambient temperature protection,
and is only invoked when the fan is
OFF. This includes the UNOCCUPIED
mode when there is no call for ca-
pacity, or any other time the fan is