Frost on the suction line indicates what about its temperature?

Frost on the suction line indicates that the temperature of the line is below the dew point and below 32°F. When the temperature of the refrigerant in the suction line drops below the dew point, moisture in the air condenses and can freeze upon contact with the cold surface, forming frost. The presence of frost signals that the line is operating at a temperature where atmospheric moisture can freeze, which typically occurs below 32°F, the freezing point of water. This condition suggests that there may be an issue such as low refrigerant levels or poor airflow, which can cause evaporator temperatures to drop excessively and lead to frost formation.