Which of the following are common signs of a refrigerant leak?

The presence of hissing sounds and ice on the evaporator coil are indeed common signs of a refrigerant leak. Hissing sounds can occur as refrigerant escapes from the system, indicating a potential breach. This sound is usually a result of the refrigerant transitioning from a high-pressure to a low-pressure area as it leaks out.

Ice on the evaporator coil typically forms when there is not enough refrigerant to absorb heat effectively. When refrigerant levels drop due to a leak, the coil can get too cold, causing moisture to freeze on it, which leads to ice accumulation. This is an indicator of a malfunctioning system, often linked to insufficient refrigerant levels due to leaks.

Unusual odors may point to other issues such as burned electrical components rather than a refrigerant leak, and while increased pressure can be related to issues in the system, it does not specifically indicate a leak. Frequent outages and decreased airflow might suggest system inefficiencies or failures but aren't directly tied to a refrigerant leak in the same way. Enhanced cooling performance contradicts the expected outcome from refrigerant loss, as a leak would generally result in decreased cooling efficiency.