Operation; Cooling Operation; Cooling Operation Errors - York Predator Z series Installation Instructions Manual

Operation

Cooling Operation

• With a demand for first stage cooling either from a
thermostat or space sensor, the low-voltage control circuit
to "C1" and "G" is completed. For first stage cooling, the
compressor is energized and the 1st stage operates (67%
capacity). The UCB will energize the VFD equipped
blower motor at low speed as set in the Smart
Equipment™ control. When the thermostat calls for the
second stage of cooling, the low-voltage control circuit to
"C2" is completed. The control board energizes the 2nd
stage of the compressor (100% capacity). If there is an
initial call for both stages of cooling, the UCB will delay
energizing the 2nd stage of the compressor by 30
seconds in order to avoid a power rush. Once the
thermostat has been satisfied, it will de-energize C1 and
C2. If the compressor has satisfied the minimum run time
(3 min default), the compressors and condenser fans are
de-energized. Otherwise, the unit operates until the
minimum run has been completed. Upon the compressor
de-energizing, the blower is stopped following the elapse
of the fan off delay for cooling.
• To be available, a compressor must not be locked-out due
to a high or low-pressure switch or freezestat trip and the
Anti- Short Cycle Delay (5 min default) must have
elapsed.
Free Cooling Operation with Economizer
• With a demand for first stage cooling either from a
thermostat or space sensor and the outside air is suitable
for free cooling, the dampers will be modulated to
maintain supply air temperature to within +/- 1 degree of
the Free Cooling SAT Upper Setpoint. If the output to the
economizer actuator is at 10 vdc and the supply air
temperature cannot be controlled to within 5 degrees of
the Free Cooling SAT Upper Setpoint, one compressor
will be energized. The economizer will then be modulated
to maintain supply air temperature to within +/- 1 degree
of the Free Cooling SAT Upper Setpoint.
• If a demand for second stage cooling occurs and the
economizer is already modulating to maintain the supply
air temperature to the Cooling SAT Upper Setpoint, the
setpoint will be changed to the Free Cooling SAT Lower
Setpoint. Any compressors that are energized will remain
energized and the economizer dampers will be modulated
to maintain supply air temperature to within +/- 1 degree
of the Cooling SAT Lower Setpoint. If the output to the
economizer actuator is at 10 vdc and the supply air
temperature cannot be controlled to within 5 degrees of
the Cooling SAT Lower Setpoint, compressor stage 2 will
be energized. The economizer will then be modulated to
maintain supply air temperature to within +/- 1 degree of
the Cooling SAT Lower Setpoint.
• If the output to the economizer actuator is at minimum
position and the supply air temperature drops more than 5
degrees below the current economizer SAT setpoint, the
Johnson Controls Ducted Systems
highest stage compressor will be de-energized as long as
the minimum run time has elapsed.
Economizer With Single Enthalpy Sensor
When the room thermostat calls for cooling, the low voltage
control circuit from "R" to "G" and "Y1" is completed. The UCB
energizes the blower motor (if the fan switch on the room
thermostat is set in the "AUTO" position) and drives the
economizer dampers from fully closed to their minimum position.
If the enthalpy of the outdoor air is below the setpoint of the
enthalpy controller (previously determined), "Y1" energizes the
economizer. The dampers will modulate to maintain a constant
supply air temperature as monitored by the discharge air sensor.
If the outdoor air enthalpy is above the setpoint, "Y1" energizes
the compressor and condenser fan motor only.
Once the thermostat has been satisfied, it will de-energize "Y1". If
the compressor has satisfied its minimum run time, the
compressor and condenser fan are de-energized. Otherwise, the
unit operates the cooling system until the minimum run times for
the compressor has been completed. After the compressor de-
energizes, the blower is stopped following the elapse of the fan
off delay for cooling, and the economizer damper goes to the
closed position. If the unit is in continues fan operation the
economizer damper goes to the min. position.
Economizer With Dual Enthalpy Sensors
The operation with the dual enthalpy sensors is identical to the
single sensor except that a second enthalpy sensor is mounted
in the return air. This return air sensor allows the economizer to
choose between outdoor air and return air, whichever has the
lowest enthalpy value, to provide maximum operating
efficiency.
Economizer With Power Exhaust
A unit equipped with an economizer (single or dual enthalpy)
and a power exhaust operates as specified above with one
addition. The power exhaust motor is energized 45 seconds
after the actuator position exceeds the exhaust fan set point on
the economizer control. As always, the "R" to "G" connection
provides minimum position but does not provide power exhaust
operation.
Motorized Outdoor Air Dampers
This system operation is the same as the units with no outdoor
air options with one exception. When the "R" to "G" circuit is
complete, the motorized damper drives open to a position set
by the thumbwheel on the damper motor. When the "R" to "G"
circuit is opened, the damper spring returns fully closed.

Cooling Operation Errors

Each cooling system is monitored for operation outside of the
intended parameters. Errors are handled as described below. All
system errors override minimum run times for compressors.
NOTE: The following components are needed to access the
control points in the Smart Equipment™ control.
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