Residential air conditioning systems have a normal superheat range of how many degrees under normal operating conditions?

• A. 6 to 10
• B. 8 to 12
• C. 4 to 8
• D. 10 to 14

Answer: (B)

Superheat is the temperature rise of the refrigerant vapor above its saturation temperature at the evaporator pressure. In typical residential air conditioning, this is kept in a range of about 8 to 12 degrees Fahrenheit under normal operating conditions. Maintaining this range ensures the refrigerant entering the compressor is in vapor form, preventing liquid from flooding the compressor, while still allowing enough heat to boil off in the evaporator for efficient cooling.

To check it, measure the suction line temperature with a thermometer near the evaporator, determine the evaporator pressure with the low-pressure gauge, find the corresponding saturation temperature for that pressure, then subtract the suction line temperature from that saturation temperature to get the superheat. If the reading is lower than about eight degrees, liquid could be reaching the compressor; if it’s higher than about twelve degrees, the system may be undercharged or the metering device could be restricting flow, leading to inadequate cooling.