Why is a non-condensable a problem?

• A. A gas that condenses in the condenser.
• B. A gas that does not condense in the condenser; it increases head pressure and reduces system efficiency
• C. A liquid that forms in the evaporator
• D. A solid contaminant

Answer: (B)

Non-condensables are gases that won’t condense at the condenser’s operating pressure, such as air or other inert leaks. In a proper condenser, refrigerant vapor must release latent heat and become liquid, but the presence of a non-condensable sits as a gas layer and takes up space near the heat transfer surfaces. This gas layer adds thermal resistance and reduces the effective temperature difference driving condensation, so the condenser can’t transfer heat as efficiently. The result is a higher condensing (head) pressure and a greater refrigerant temperature leaving the condenser, which makes the compressor work harder and wastes energy. Overall system efficiency drops, and you can see higher power use and potential operating issues as a consequence.

The other descriptions describe a substance that condenses as it should, a liquid forming in the evaporator, or a solid contaminant, which are different situations from a non-condensable gas.