If noncondensable gases are present in the system, which statement best describes the expected condenser pressure relative to the PT chart for the same refrigerant and temperature?

• A. Higher than the PT chart value.
• B. Lower than the PT chart value.
• C. Equal to the PT chart value.
• D. Unrelated to the PT chart value.

Answer: (A)

Noncondensable gases in the condenser impede heat transfer, creating an insulating layer and lowering the condenser’s effectiveness. Because the refrigerant can’t condense as easily, the system must build a higher pressure to achieve condensation at the same temperature. The PT chart shows the saturated vapor pressure for a pure refrigerant at a given temperature; with noncondensables present, the actual condenser pressure ends up higher than that chart value. This is why the condenser pressure is higher than the PT chart value for the same refrigerant and temperature.