Which of the following is an indicator of a leak in a high pressure system with a capillary tube?

• A. High discharge pressure
• B. Excessive superheat
• C. Low suction pressure
• D. Frost on evaporator coil

Answer: (B)

Excessive superheat shows up when a capillary-tube system runs with too little refrigerant. The fixed metering device means the system relies on a precise amount of liquid to fully evaporate in the evaporator. If there’s a leak, the charge drops and the evaporator is starved of liquid. What leaves the evaporator is predominantly vapor, so the suction gas is much hotter than the evaporating temperature at that pressure. That larger difference is measured as high superheat, which is a clear sign of undercharge due to a leak in this kind of system.

High discharge pressure isn’t a direct telltale of a leak, since it reflects conditions on the high side and can be influenced by ambient load or overcharging. Low suction pressure can occur with a leak, but it’s not as specific to a capillary-tube system and can arise from other factors. Frost on the evaporator coil is more about freezing conditions or airflow and isn’t as directly tied to a leak as excessive superheat is.