Air or other noncondensable gases in a capillary tube 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: (B)

Air or other noncondensables in a capillary-tube system hinder heat transfer in the condenser. That makes the condenser operate at a higher temperature and pressure (the high side must work harder to reject heat). Because the metering device is fixed, the increased head pressure pushes more refrigerant into the evaporator, raising the evaporator pressure as well. The compressor then has to compress against this higher suction and discharge pressure, so both sides rise. This combination—elevated pressures on both the high and low sides—is the signal of noncondensables present in the system, which is why the best answer shows high suction pressure and high discharge pressure.