What might explain low suction pressure during operation of a refrigeration unit?

Low suction pressure in a refrigeration unit can indeed be attributed to a clogged filter drier. The filter drier plays a vital role in the refrigeration system by removing moisture and contaminants from the refrigerant before it circulates. When the filter drier becomes clogged, it restricts the flow of refrigerant. This leads to a drop in the flow rate through the evaporator, resulting in lower evaporation temperature and consequently lower suction pressure.

In contrast, excess refrigerant in the system typically causes increased pressure rather than low suction pressure, as it can lead to liquid refrigerant being pushed back into the suction line. High ambient temperatures are likely to increase, not decrease, suction pressure since they can elevate system pressure and temperature. An improperly adjusted expansion valve can lead to issues such as refrigerant flooding or inadequate refrigerant flow, but would generally not specifically cause low suction pressure to the extent that a clogged filter drier would.