A refrigeration system comprises a compressor, a con
denser, a receiver, an evaporator, and an adjustably
controllable expansion valve connected in the refriger
ant supply line from the receiver to the evaporator. An
electronic control system adjustably controls the expan
sion valve so as to maintain the maximum amount of
liquid refrigerant in the evaporator while preventing
flow of liquid refrigerant to the compressor. The elec
tronic control system measures both the actual refriger
ant temperature and refrigerant vapor pressure at a
common point near the evaporator outlet port, converts
the measured vapor pressure to a saturation tempera
ture, determines the differential between the two tem
peratures and adjusts the expansion valve in accordance
therewith, i.e., closing or opening in response to differ
entials below or above a set point, respectively.