What can cause frost build-up around the evaporator coil?

Frost build-up around the evaporator coil is primarily caused by a combination of low refrigerant charge or dirty filters. When there is a low refrigerant charge, the necessary amount of refrigerant to absorb heat from the surrounding air is insufficient. This leads to reduced cooling capacity and can cause the temperature of the evaporator coil to drop below freezing, resulting in frost formation.

Additionally, dirty filters can obstruct airflow, which reduces the amount of warm air moving over the evaporator coil. When warm air is not adequately circulating, it cannot effectively raise the temperature of the coil, leading to a similar frost formation as seen with low refrigerant levels. This combination of low refrigerant and restricted airflow creates an environment conducive to frost accumulation around the evaporator coil.

In contrast, situations such as excessive refrigerant charge, consistent airflow, or high ambient temperatures do not typically lead to frost formation at the evaporator coil. Excessive refrigerant can create other operational issues and does not correlate directly with frost build-up, while consistent airflow generally promotes proper operation and reduces the likelihood of frost. High ambient temperatures can facilitate proper cooling performance, so they are unlikely to contribute to frost accumulation in a properly functioning system.