HVAC - EPA Certification Practice Exam

The presence of ice on the evaporator coil is a clear indication that an air conditioner is low on refrigerant. Refrigerant is responsible for absorbing heat from the indoor air as it passes over the evaporator coil. When the refrigerant level drops, it can lead to a situation where the coil does not absorb enough heat effectively. This can cause the temperature of the coil to drop significantly, allowing moisture in the air to freeze on the coil's surface, leading to the buildup of ice. This ice can restrict airflow and eventually lead to the system's improper functioning or failure.

In contrast, while unusual noises, increased humidity levels, and short cycling can indicate other issues with an HVAC system, they are not specific indicators of low refrigerant. Unusual noises might suggest mechanical problems, increased humidity levels could indicate a malfunctioning air handler or inadequate cooling, and short cycling could be caused by various issues, including thermostat problems or an oversized system, but none directly correlates to refrigerant levels like the presence of ice on the evaporator coil does.