York YCAS0130 manual Operation

Operation

FORM 201.19-NM1 (204)

OPERATION

GENERAL DESCRIPTION

The units are designed to work independently, or in conjunction with other equipment via a YORK ISN building management system or other automated con- trol system. When operating, the unit controls monitor the chilled liquid system temperature at the unit and take the appropriate action to maintain this temperature within desired limits. This action will involve running one or more compressors at a suitable load step to match the cooling effect of the refrigerating systems to the heat load on the liquid system. The heat removed from the chilled liquid is then rejected from the air cooled condenser coils.

The following sections give an overview of the operation of the unit. For detailed information, reference should be made to the Chiller Control Panel Programming and Data Access Operating Instructions for the unit (pages 122 - 192).

START-UP

Check the main power supplies to the unit are ‘ON’, all refrigerant service valves are open (counter-clockwise one turn short of fully open) and chilled liquid flow has been established (unless the unit chilled liquid pump start control is being used, in which case just ensure the pump supply is on). Ensure only the correct system switches (SYS 1-2) on the microprocessor circuit board are in the ‘ON’ position.

Press the ‘STATUS’ key on the keypad and then switch the unit ON/OFF switch below the keypad to the ON position.

The controller 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 that cooling load is required (i.e. that the chilled liquid temperature is outside the set limits). Any problems found by the pre-check will be displayed if present. If no problems are present and cooling duty is required the lead compressor will start.

The display will show the anti-coincidence timer status for the lag compressor, followed by ‘NO COOL LOAD’ until it is called to operate by the control system.

NORMAL RUNNING AND CYCLING

Once the unit has been started, all operations are fully automatic. After an initial period at minimum capacity on the lead compressor, the control system will adjust the unit load depending on the chilled liquid temperature and rate of temperature change. If high heat load is pres- ent, the controller will increase the capacity of the lead compressor and/or start-up the other compressor.

If very little heat load is present, the lead compressor will continue at minimum capacity or may simply stop again to avoid overcooling the liquid. If the latter is the case, one compressor will restart automatically should the liquid temperature rise again.

Once a compressor is running, discharge pressure rises as refrigerant is pumped into the air cooled condenser coils. This pressure is controlled by stages of fans to ensure maximum unit efficiency while maintaining suf- ficient pressure for correct operation of the condensers and expansion valves.

When a compressor is running, the controller monitors oil pressure, motor current, and various other system parameters such as discharge pressure, chilled liquid temperature, etc. Should any problems occur, the control system will immediately take appropriate action and display the nature of the fault (Section 8).

SHUTDOWN

The unit can be stopped at any time by switching the UNIT ON/OFF switch just below the keypad to the OFF position. The compressor heater will energize to prevent refrigerant condensing in the compressor rotors. If ambient temperatures are low, the evaporator heater mats will also energize to prevent the possibility of liq- uid freezing in the vessels. The mains power to the unit should not normally be switched OFF, even when the unit is not required to run.

The system switches (S2-S5) on the microboard can be used to cycle a system OFF. An automatic pumpdown will occur using the system switches.

If mains power must be switched OFF, (for extended maintenance or a shutdown period), the compressor suc- tion, discharge and motor cooling service stop valves should be closed (clockwise) and if there is a possibility of liquid freezing due to low ambient temperatures, the evaporators should be drained. Valves should be opened and power must be switched on for at least 8 Hours (36 Hours if ambient temperature is over 86°F [30°C]) before the unit is restarted.

46 YORK INTERNATIONAL