HVAC - EPA Certification Practice Exam

A frozen HVAC unit can occur due to several factors that inhibit the normal cooling process. The correct answer highlights two key issues: a low refrigerant charge and airflow restriction.

When the refrigerant charge is low, the system doesn't have enough refrigerant to absorb heat from the indoor air effectively. This can cause the evaporator coil to drop in temperature significantly, leading to moisture freezing on the coil. If airflow is restricted—whether due to blocked ducts, closed vents, or dirty filters—there is insufficient air passing over the evaporator coil. This situation can result in the coil not getting the required warm air necessary to raise its temperature above freezing, thus also causing frost or ice formation.

Both low refrigerant levels and airflow restrictions create conditions that prevent the system from operating efficiently, which can lead to freezing. Understanding these mechanics is crucial for troubleshooting and maintaining HVAC systems effectively.