York YCAL0080SC, YCAL0014SC manual Unit Operating Sequence

FORM 150.62-NM1

UNIT OPERATING SEQUENCE

The operating sequence described below relates to op- eration on a hot water start after power has been ap- plied, such as start-up commissioning. When a com- pressor starts, internal timers limit the minimum time before another compressor can start to 1 minute.

1.For the chiller system to run, the Flow Switch must be closed, any remote cycling contacts must be closed, the Daily Schedule must not be scheduling the chiller off, and temperature demand must be present.

2.When power is applied to the system, the micropro- cessor will start a 2 minute timer. This is the same timer that prevents an instantaneous start after a power failure.

3.At the end of the 2 minute timer, the microprocessor will check for cooling demand. If all conditions allow for start, the first compressor on the lead system will start and the liquid line solenoid will open. The com- pressor with the least run time in that system will be the first to start. Coincident with the start, the anti- coincident timer will be set and begin counting down- ward from “60” seconds to “0” seconds.

If the unit is programmed for Auto Lead/Lag, the system with the shortest average run-time of the com- pressors will be assigned as the “lead” system. A new lead/lag assignment is made whenever all sys- tems shut down.

4.Several seconds after the compressor starts, that systems first condenser fan will be cycled on (out-

door air temperature > 25°F (-4°C)). See the section on Operating Controls for details concerning con- denser fan cycling.

5.After 1 minutes of compressor run time, the next compressor in sequence will start when a system has to load. This compressor will be the one with the least run time that is currently not running in that sys- tem. Additional compressors will be started at 60 second intervals as needed to satisfy temperature setpoint.

6.If demand requires, the lag system will cycle on with the same timing sequences as the lead system. Re- fer to the section on Capacity Control for a detailed explanation of system and compressor staging.

7.As the load decreases below setpoint, the compres- sors will be shut down in sequence. This will occur at intervals of either 60, 30, or 20 seconds based on water temperature as compared to setpoint, and con- trol mode. See the section on Capacity Control for a detailed explanation.

8.When the last compressor in a “system” (two or three compressors per system), is to be cycled off, the system will initiate a pump-down. Each “system” has a pump-down feature upon shut-off. On a non-safety, non-unit switch shutdown, the LLSV will be turned off, and the last compressor will be allowed to run until the suction pressure falls below the suction pres- sure cutout or for 180 seconds, which ever comes first.

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