Which of the following is not a symptom of a hermetic system that is low on refrigerant?

• A. High head pressure
• B. Frost on the suction line
• C. Low suction pressure
• D. Higher discharge temperature

Answer: (A)

When refrigerant charge is low, the evaporator doesn’t have enough refrigerant to absorb heat properly. That pushes the evaporating pressure and the suction pressure down, so the suction line and the evaporator surface get very cold. Moisture in the air on the cold surface can freeze, forming frost on the suction line. So low suction pressure and frost on the suction line are direct signs of a low charge.

The discharge temperature can rise because the compressor is pushing less refrigerant mass, but the gas being compressed still encounters heat and pressure. With less refrigerant circulating, the condenser has less heat to reject per cycle, which can cause the discharge gas to remain hotter than normal.

Head pressure, or high-side pressure, is mainly governed by condenser conditions and ambient temperature. A low refrigerant charge does not typically drive head pressure higher; it often stays the same or even drops depending on the system and conditions.