ESCO Refrigeration Practice Test

When a thermostatic expansion valve or capillary tube is used, the system’s flow is determined by the metering device, and the refrigerant charge sets how much refrigerant is available to circulate. If the charge is too low, there isn’t enough liquid refrigerant in the system to properly flood the evaporator, so the evaporator pressure drops (the suction side is lower). With less vapor being generated and circulated, the condenser side has less vapor to condense, so the high-side pressure that the condenser must maintain also falls. In short, a low refrigerant charge reduces the amount of refrigerant and heat rejection, leading to a lower head (high-side) pressure. The other effects mentioned—higher head pressure, increased discharge temperature, or faster compressor speed—don’t naturally result from a low charge and are not the expected outcome in this setup.