Which of the following is a sign of low refrigerant in an HVAC system?

The presence of lower than normal suction pressure along with frost on the evaporator is a clear indication of low refrigerant in an HVAC system. When the refrigerant levels are insufficient, it does not absorb heat efficiently, leading to low pressure conditions on the suction side. This reduced pressure can cause the temperature of the refrigerant to drop significantly, allowing moisture in the air to freeze on the evaporator coil, resulting in frost build-up.

This phenomenon is contrary to what would be expected in a properly charged system, where the refrigerant effectively circulates and maintains appropriate pressure and temperature levels necessary for optimal heat exchange processes. Recognizing these specific signs is crucial for diagnosing low refrigerant levels, which can prevent operational efficiency and potential system damage in HVAC applications.