Air in the system will cause which of the following discharge pressures in a refrigeration system?

• A. Lower discharge pressures
• B. Higher discharge pressures
• C. Unchanged discharge pressures
• D. Unpredictable discharge pressures

Answer: (B)

Air in the system acts as a non-condensable gas, which blocks heat transfer in the condenser. Because heat can’t be rejected as effectively, the condenser pressure rises to push heat out despite the air. That higher condenser (head) pressure means the compressor must discharge refrigerant at a higher pressure as well. So discharge pressures increase when air is present. It wouldn’t lower or keep the pressure the same under normal operation; the effect of non-condensables is to elevate the pressure on the high side until the air is removed.