Which of the following is the least likely cause of high suction pressure in a refrigeration system?

High suction pressure in a refrigeration system can occur due to several factors, and understanding each option's role is essential.

When there is not enough system load, it typically means that the demand for cooling is low. This reduced load can result in the system cooling too efficiently or, in some cases, causing the compressor to operate in an inefficient range. However, generally, a lower load corresponds to lower suction pressure, as the evaporator is not transferring heat efficiently and may not evaporate the refrigerant as quickly. Hence, it is unlikely to contribute to increased suction pressure.

Conversely, not having enough refrigerant would lead to inadequate cooling and could potentially create a lower suction pressure due to insufficient refrigerant returning to the compressor. Compressor issues can manifest in various ways, including poor compression efficiency or mechanical failures, leading to abnormal pressure readings. A faulty expansion valve could cause improper refrigerant flow and pressure imbalances, potentially increasing suction pressure by allowing too much refrigerant into the evaporator.

Thus, among the choices provided, having not enough system load is the least likely cause of high suction pressure, as it typically would not contribute to higher pressure in the suction line.