Which of the following accurately describes a non-condensable gas?

A non-condensable gas is defined as a gas that does not condense into a liquid under the conditions present in a refrigeration or air conditioning system. Therefore, it will always remain in the vapor phase throughout the system. This characteristic is critical because the presence of non-condensable gases can impair the efficiency and performance of refrigeration systems; they do not contribute to heat exchange processes like the refrigerant gases do.

Regarding the other choices: the first option suggests a gas that can be easily condensed, which contradicts the definition of non-condensable gases. The third option implies that a non-condensable gas aids in the cooling process, but such gases do not facilitate refrigerant cooling and can actually hinder system performance. The final option states that a non-condensable gas increases system pressure, which can be a consequence of having these gases in the system, but it does not accurately describe the defining feature of non-condensable gases themselves. Thus, the accurate description aligns with the understanding that non-condensable gases remain in vapor form throughout the system.