An apparatus comprising: a compressor configured to compress a refrigerant; a load configured to: use the refrigerant from the compressor to remove heat from a space proximate the load; and send the refrigerant to the compressor; a heat exchanger, configured to: receive the refrigerant from the compressor; transfer heat from a fluid to the refrigerant; and discharge the refrigerant to the compressor; a heater configured to add heat to the fluid circulating between the heater and the heat exchanger; a pump configured to circulate the fluid between the heater and the heat exchanger a pressure sensor configured to measure a pressure of the refrigerant; a temperature sensor configured to measure a temperature of the refrigerant; a valve disposed between the compressor and the heat exchanger; and a controller communicatively coupled to the pressure sensor and the temperature sensor, the controller configured to: determine a saturation temperature based on the received measured pressure; calculate a differential between the measured temperature and the determined saturation temperature; compare the calculated differential to a differential set point; and based on the comparison between the calculated differential and the differential set point, increase a flow of the refrigerant from the compressor to the heat exchanger by opening the valve. a compressor configured to compress a refrigerant; a load configured to: use the refrigerant from the compressor to remove heat from a space proximate the load; and send the refrigerant to the compressor; use the refrigerant from the compressor to remove heat from a space proximate the load; and send the refrigerant to the compressor; a heat exchanger, configured to: receive the refrigerant from the compressor; transfer heat from a fluid to the refrigerant; and discharge the refrigerant to the compressor; receive the refrigerant from the compressor; transfer heat from a fluid to the refrigerant; and discharge the refrigerant to the compressor; a heater configured to add heat to the fluid circulating between the heater and the heat exchanger; a pump configured to circulate the fluid between the heater and the heat exchanger a pressure sensor configured to measure a pressure of the refrigerant; a temperature sensor configured to measure a temperature of the refrigerant; a valve disposed between the compressor and the heat exchanger; and a controller communicatively coupled to the pressure sensor and the temperature sensor, the controller configured to: determine a saturation temperature based on the received measured pressure; calculate a differential between the measured temperature and the determined saturation temperature; compare the calculated differential to a differential set point; and based on the comparison between the calculated differential and the differential set point, increase a flow of the refrigerant from the compressor to the heat exchanger by opening the valve. determine a saturation temperature based on the received measured pressure; calculate a differential between the measured temperature and the determined saturation temperature; compare the calculated differential to a differential set point; and based on the comparison between the calculated differential and the differential set point, increase a flow of the refrigerant from the compressor to the heat exchanger by opening the valve.