What is a typical result of an incorrect refrigerant charge?

• A. Undercharge can cause low head pressure and high superheat; overcharge can cause high head pressure and reduced efficiency.
• B. Undercharge always improves performance.
• C. Overcharge reduces head pressure to zero.
• D. Charge amount does not affect system pressures.

Answer: (A)

The main idea is how the amount of refrigerant affects how the system absorbs and rejects heat, which shows up as pressures on the high and low sides and as superheat at the evaporator outlet. If the system is undercharged, there isn’t enough refrigerant to fully fill the evaporator, so the suction pressure on the low side drops and the refrigerant that leaves the evaporator is highly vaporized, leading to high superheat. The condenser isn’t seeing as much refrigerant either, so the high-side pressure tends to be lower. If the system is overcharged, more liquid circulates than the compressor can handle efficiently, raising the high-side pressure (head pressure) and generally reducing overall efficiency because the compressor has to work harder to move the excess refrigerant. So the typical results described—undercharge yielding low head pressure and high superheat, overcharge yielding high head pressure and reduced efficiency—best capture how incorrect charge affects performance.