An apparatus for cooling a computer system includes a primary cooling loop. The primary cooling loop includes an evaporator configured to cool at least a component of the computer system, an ambient cooled condenser connected to the evaporator, a first pump to provide a coolant flow within the cooling loop, a pressure regulator configured to maintain a selected pressure in the primary cooling loop, and a controller responsive to changes in outdoor ambient conditions and an amount of heat dissipated by the computer system and configured to dynamically adjust the pump and pressure regulator in response thereto.