Unit Operating Sequence - York YCAE065 Manual

outside of these limits is undesirable and could cause damage.
If mains power must be switched OFF for extended maintenance or an extended shutdown period,
the compressor suction and discharge service stop valves should be closed (clockwise). If there is a
possibility of liquid freezing due to low ambient temperatures, the coolers should be drained or power
should be applied to the unit. Before placing the unit back in service, valves should be opened and
power must be switched on (if power is removed for more than 8 hours) for at least 8 hours before
the unit is restarted.
Flow Switch
A unit flow switch has been fitted on the cooler outlet. If the units are connected for central control, it
is recommended to install an additional flow switch on the main outlet. Make sure the switch is wired
into the control panel correctly using shielded cable.
There should be a straight run of at least 5 pipe diameters on either side of the flow switch.
Temperature Sensor(s)
Leaving liquid temperature sensor is used for modular control. Ensure the sensor is coated with heat
conductive compound and is inserted to the bottom of the water outlet sensor well in the main pipe.
This sensor also provides some anti-freezing protection and must always be fully inserted in the water
outlet sensor well.
Control Supply
Verify the control panel display is illuminated.

UNIT OPERATING SEQUENCE

The operating sequence described below relates to operation on a starting process after power has
been applied, such as start-up commissioning. When a compressor starts, internal timers limit the
minimum time before another compressor can start to 40 seconds (20-120 seconds, adjustable).
1. When power is applied to the system, the micro- processor will perform a pre-check to ensure that
the daily/holiday schedule and any remote interlocks will allow the unit to run, all safety cut-outs are
satisfied and no faults are unsettled. Any problems found by the pre-check will be displayed if present.
2. For the unit to run, there must be an 'ON' command given by controller or BAS (Building Automation
System) for the unit to respond to. Once the unit is ON, the water pump contactor will close instantly.
The unit will then detect the status of the flow switch to ensure sufficient liquid flow is supplied.
3. If no problems are present and duty is required the compressor will start. After an initial period of
operation with the compressor, the control system will adjust the unit load depending on the liquid
temperature and rate of temperature change. If high load is present, the controller will start the next
compressor. If very little load is present, the compressor may continue to operate or may simply stop.
If the latter is the case, one compressor will restart automatically should the liquid temperature require.
4. When a compressor is running the controller monitors suction pressure and various other system
parameters such as discharge pressure, liquid temperature, etc. Should any problems occur, the
control system will immediately take appropriate action and display the nature of the fault.
Cooke Industries - Phone: +64 9 579 2185 Email: sales@cookeindustries.co.nz Web: www.cookeindustries.co.nz