CNT-SVX04A-EN
Sequence of operation
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In 4-pipe applications it is assumed that both heat and cool capacity are
available. See “Valve operation” on page 63 for more information on isolation
valve operation.
Upon power-up, the controller calibrates the face and bypass damper to the full
bypass position by overdriving the damper 135% of the stroke time. During
normal operation, whenever the Tracer ZN.520 zone controller generates a face
and bypass damper position request of zero or 100%, the unit calibrates the
actuator by overdriving the damper 135% of the stroke time.
DX operation
Tracer ZN.520 zone controller supports direct expansion (DX) compressor
operation for cooling only.
The controller does not use both the DX compressor and the economizer at the
same time. This prevents problems where the entering air temperature is too
low for the evaporator coil to operate as designed, leading to short cycling of
the compressor due to low discharge air temperatures.
Electric heat operation
The Tracer ZN.520 zone controller supports 1- or 2-stage electric heat operation
for heating.
To control the space temperature, electric heat is cycled to control the discharge
air temperature. The rate of cycling is dependent upon the load in the space and
the temperature of the incoming fresh air from the economizer (if any).
Two-pipe changeover units with electric heat use the electric heat only when
hot water is not available. The use of hot water AND electric heat is not
supported. See “Coil changeover” on page 58 for further explanation.
Output overrides
The controller can override the binary outputs, typically for test and
commissioning, using Trane's Tracer Summit building automation system or
from Rover service tool. For more information on the output overrides, refer to
the product-specific literature for the building automation system and the
service tool.
Manual output test
Manual output test allows the user to manually exercise the outputs in a
predefined sequence. For more information, refer to “Manual output test” on
page 88.
