A water chiller with a reciprocating compressor, a thermostatic expansion valve and an air cooled condenser. A restriction in the liquid line would result in:

• A. High Suction Superheat
• B. Low Suction Pressure
• C. High Discharge Pressure
• D. Low Head Pressure

Answer: (A)

When the liquid line is restricted, the evaporator isn’t fed with enough liquid refrigerant. That means the evaporator can’t absorb as much heat as intended and can’t fully vaporize the liquid at the evaporating pressure. The refrigerant leaving the evaporator is therefore more vapor and hotter than the saturated vapor at the suction pressure, so the actual suction gas temperature rises relative to its saturation temperature. In other words, the difference between the suction gas temperature and the evaporating (saturation) temperature—the suction superheat—increases. That’s why a liquid-line restriction tends to produce high suction superheat. The other options aren’t the primary effect of this restriction: they relate more directly to condenser or overall system pressures rather than the heat state of the vapor returning to the compressor.