York YLAA Operation Manual page 12

FORM 150.72-EG6 (516)
Equipment Overview (Cont'd)
Maximum reliability is achieved through intelligent control. Run hours and starts are av-
eraged across all compressors automatically, and between both pumps of the optional
dual pump hydro-kit. When compressors are cycled off, an anti-recycle timer ensures
the motors have time to cool before starting again, for the maximum service life. At unit
shutdown, the unit pumps down automatically to prevent liquid refrigerant from entering
the compressors at restart, which can cause premature bearing wear and other compres-
sor damage.
Liquid temperature sensors provide feedback to the controller, and logic predicts when
additional capacity will be required based on how quickly the unit has loaded or unloaded
in the past. This prevents unnecessary compressor cycling and helps maintain setpoint
accurately.
If there is a problem that prevents the unit operating properly, the controls are designed to
allow the unit to operate safely while making as much capacity as possible. For example,
if airflow to the condenser coil is diminished due to a dirty coil, the chiller will unload slightly
to provide maximum capacity possible while remaining within the unit operating envelope.
If a fault prevents the unit from starting or causes it to shutdown, the chiller will attempt to
restart three times. If it cannot start, a manual reset is required to alert the operator about
the fault condition. The fault history is stored in the unit controller RTC memory for the
last six fault shutdown conditions. An RS-232 port provides capability to print hard copy
reports (printer available separately).
All controls are contained in a NEMA 3R cabinet with a hinged outer door and includes a
liquid crystal display (LCD) with light emitting diode (LED) backlighting for outdoor view-
ing. There are two display lines, each with 20 text characters per line, and a color coded
12-button non-tactile keypad with sections for display, entry and printing.
DISPLAY/PRINT provides quick access to frequently needed information:
• Chilled liquid temperatures
• Ambient temperature
• System pressures (each circuit)
• Operating hours and starts (each compressor)
• Operating data for the systems
ENTRY section allows entering setpoints or modifying system values.
SETPOINTS updating can be performed to:
• Chilled liquid temperature setpoint and range
• Remote reset temperature range
• Set daily schedule/holiday for start/stop
• Manual override for servicing
• Low and high ambient cut-outs
12 JOHNSON CONTROLS