The purpose of a compressor in a chiller is to lower the pressure and temperature of liquid refrigerant to a point below the temperature of the brine in order to allow heat to flow from the brine to the refrigerant.
The compressor then increases the pressure and temperature of the refrigerant gas to a point above the ambient air and water temperatures in order for the heat to flow out of the refrigerant into the outdoor air and water. This allows the refrigerant to condense.