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Tracer
®
ZN.520
66 UNT-IOM-6
Unit diagnostics can affect the Tracer
®
ZN.520 controller operation,
causing unit operation to be defined as abnormal. Refer to the
Troubleshooting section for more information about abnormal unit
operation.
The heating output is controlled based on the heating capacity. At 0%
capacity, the heating output is off continuously. Between 0 and 100%
capacity, the heating output is controlled according to modulating
valve logic (modulating valves) or cycled on (2-position valves). As the
load increases, modulating outputs open further and binary outputs
are energized longer. At 100% capacity, the heating valve is fully open
(modulating valves) or on continuously (2-position valves).
The Tracer
®
ZN.520 fan output(s) normally run continuously during the
occupied and occupied standby modes, but cycle between high and
off speeds with heating/cooling during the unoccupied mode. When in
the occupied mode or occupied standby mode and the fan speed is
set at the high, medium, or low position, the fan runs continuously at
the selected speed. Refer to the Troubleshooting section for more
information on abnormal fan operation.
When the units supply fan is set to auto, the controllers configura-
tion determines the fan speed when in the occupied mode or occu-
pied standby mode. The fan runs continuously at the configured
heating fan speed or cooling fan speed. For all fan speed selections
except off, the fan cycles off during unoccupied mode.
The economizer outdoor air damper is never used as a source of
heating. Instead, the economizer damper (when present) is only used
for ventilation; therefore, the damper is at the occupied minimum
position in the occupied mode. The damper control is primarily
associated with occupied fan operation.
For multiple fan speed applications, the Tracer
®
ZN.520 controller
offers additional fan configuration flexibility. Separate default fan
speeds for heating and cooling modes can be configured. The fan
runs continuously for requested speeds (off, high, medium, or low).
When the fan mode switch is in the Auto position or a hardwired fan
mode input does not exist, the fan operates at the default configured
speed. See Table 21 on page 67 for default fan configuration for heat
and cool mode. During unoccupied mode, the fan cycles between
high speed and off with heating and cooling fan modes. If the re-
quested speed is off, the fan always remains off.
During dehumidification, when the fan is on Auto, the fan speed can
Fan Mode Operation