Abstract: A method is disclosed for controlling a discharge pressure of a compressor relative to a suction pressure of the compressor. The discharge pressure and suction pressure of the compressor are monitored and compared with a predetermined maximum pressure ratio of discharge pressure to suction pressure. If the pressure ratio of discharge pressure to suction pressure exceeds a predetermined pressure ratio limit less than the maximum pressure ratio, a controller unloads the compressor. The predetermined pressure ratio limit is determined relative to the measured suction pressure. The discharge pressure and suction pressure are further monitored and the compressor is inhibited from being reloaded for a predetermined time delay. After the predetermined time delay has elapsed, the compressor is reloaded only if i) the discharge pressure falls below a predetermined reload pressure and ii) the chiller system requires additional cooling capacity.

Abstract: A control algorithm for controlling an economizer circuit in a chiller system is provided. The control algorithm opens and closes a port valve in the economizer circuit in response to predetermined criteria to engage and disengage the economizer circuit. The predetermined criteria can include an operating parameter of a compressor and a level of liquid refrigerant in a flash tank.