A refrigeration system controlled by a TXV shows high discharge pressure and high normal sub-cooling. What is the most probable cause?

• A. Dirty condenser
• B. Refrigerant overcharge
• C. High ambient temperature
• D. Low refrigerant charge

Answer: (B)

When a TXV system shows high discharge (head) pressure and a high amount of subcooling, the most likely issue is refrigerant overcharge. With too much refrigerant in the system, the condenser has more liquid to condense and reject heat for, so the condenser must work harder. That extra workload pushes the condensed pressure higher, raising the discharge pressure. As the excess liquid circulates through the condenser, it is cooled further below its saturation temperature before leaving the condenser, which shows up as greater subcooling.

The expansion valve is still trying to regulate flow to maintain proper superheat, but it can’t fix the problem caused by an excess amount of refrigerant circulating in the system. Therefore, you end up with both elevated head pressure and increased subcooling.

If the condenser were dirty, heat rejection would be impaired and subcooling would typically decrease or stay normal rather than increase. A high ambient temperature can raise head pressure but doesn’t inherently explain unusually high subcooling. Low refrigerant charge would lower head pressure and subcooling.