Which of the following conditions would most likely indicate low refrigerant levels?

Excessive ice on the evaporator coils is a clear indicator of low refrigerant levels. When the refrigerant level is low, it cannot effectively absorb heat from the indoor air, leading to a drop in pressure on the evaporator side. This low pressure causes the temperature of the evaporator to fall significantly, resulting in moisture in the air freezing on the coils. This accumulation of ice can further obstruct airflow and impair the system's efficiency, ultimately requiring attention.

In contrast, the other conditions mentioned might not be directly linked to low refrigerant levels. High compressor noise can indicate mechanical issues within the compressor itself rather than problems related to refrigerant. A low temperature differential in the system typically reflects underperformance or other inefficiencies but doesn’t specifically indicate low refrigerant. Frequent cycling of the compressor can occur due to a variety of reasons, such as thermostat issues or improper settings, and while it may be a symptom of low refrigerant, it is not as definitive as the presence of excessive ice on the evaporator.