Non-condensables can cause which of the following in the discharge line?

• A. Decrease
• B. Increase
• C. No change in discharge pressure
• D. Unstable suction pressure

Answer: (B)

Non-condensables are gases that won’t condense in the condenser at the operating temperature (for example, air). When these gases are present in the discharge path, they accumulate in the condenser and hinder heat transfer. This prevents the refrigerant from fully condensing, so the condenser pressure rises. The compressor then has to push against this higher pressure, which shows up as an increase in discharge pressure in the discharge line. So the immediate effect is an increased discharge pressure. The other options don’t fit because a decrease or no change in discharge pressure doesn’t reflect the added gas causing poorer condensation, and while suction conditions can be affected in different ways, the primary and most direct consequence in the discharge line is higher pressure.