Which combination of system parameters is typically observed when noncondensable gases are present in the refrigerant circuit?

• A. Head pressure increases and capacity decreases.
• B. Head pressure decreases and capacity increases.
• C. Suction pressure rises while head pressure falls.
• D. No change in pressure or capacity.

Answer: (A)

Noncondensable gases in the refrigerant circuit hinder heat transfer in the condenser. They form an insulating layer on the high‑pressure side, making condensation less efficient. To push the refrigerant to condense despite this resistance, the condenser (head) pressure rises. At the same time, less liquid refrigerant makes it to the evaporator, so the system can’t absorb as much heat, and the compressor ends up delivering less cooling effect, i.e., reduced capacity. The other scenarios don’t match what typically happens: head pressure doesn’t drop while capacity increases, and a simple no-change situation isn’t realistic when noncondensables are present.