The refrigeration or heat pump installation includes a liquid separator that has a vapor chamber having a port connected to the outlet of the evaporator and an outlet connected through a suction conduit to a compressor. The separator also has an intermediate chamber beneath the vapor chamber for receiving liquid from the vapor chamber by the way of a first switching valve, the intermediate chamber being connected to the inlet of the evaporator for the purpose of recirculating liquid. A second switching valve forms part of the expansion apparatus for controlling the flow of fluid either directly to the intermediate chamber or through the first switching valve to the intermediate chamber. The two switching valves are operated to open and closed conditions in the opposite sense for controlling and almost continuous pulsating recirculation of liquid through the evaporator. The expansion apparatus is connected through a condenser to the outlet of the compressor.