What is the most likely cause of frost on the suction line and compressor during operation?

Frost on the suction line and compressor during operation is most likely caused by not enough refrigerant in the system. When the refrigerant charge is low, it leads to insufficient cooling capability and reduced pressure within the evaporator. As a result, the temperature of the refrigerant can drop significantly, allowing moisture in the air to freeze on the surface of the suction line and compressor.

This phenomenon occurs because as the refrigerant evaporates in low-pressure conditions, it absorbs heat more than it normally would, causing the temperature of the line to fall below freezing. Consequently, frost forms as the moisture in the air condenses and freezes onto these components.

While other factors, such as excess refrigerant, blocked airflow, or improper insulation, can affect system performance and efficiency, they generally do not directly lead to frost formation in the same manner that a low refrigerant charge does. Excess refrigerant tends to cause higher pressures and temperatures, while airflow issues and insulation concerns typically result in heat loss rather than the significant cooling needed for frost formation.