In a water chiller system using refrigerant R123, a leak in the evaporator shell is most likely to cause which condition?

• A. Lower suction pressure
• B. Higher than normal high side pressure
• C. No change
• D. Lower high side pressure

Answer: (B)

A leak in the evaporator shell lets air (non-condensable gases) enter the refrigerant circuit. Those non-condensables travel with the refrigerant vapor to the condenser, where they linger and hinder heat rejection. Because the condenser can’t reject heat as efficiently, the condensing pressure rises, pushing the high-side (discharge) pressure higher than normal. Even though losing some refrigerant due to the leak can lower suction pressure, the dominant effect here is the presence of non-condensables that raise the head pressure. In a water chiller using R123, this manifests as a higher than normal high-side pressure rather than no change or a lower high-side pressure.