A low refrigerant charge in an air conditioning system will cause these symptoms...

• A. Low suction pressure and low discharge pressure
• B. High suction pressure and high discharge pressure
• C. High suction pressure and lower than normal discharge pressure
• D. Low suction pressure and high discharge pressure

Answer: (A)

Low refrigerant charge reduces the amount of refrigerant circulating through the system, so the evaporator can’t generate as much vapor. That causes the evaporator pressure, or suction pressure, to drop. With less refrigerant flowing to the compressor, the compressor works with a smaller load, which pulls the discharge side down as well, leading to a lower discharge pressure. In short, undercharge means less heat transfer in the evaporator and less mass flow through the compressor, so both suction and discharge pressures decrease.