What may be a sign of a functioning evaporator coil in a refrigeration system?

Frost build-up on the coil is a positive indicator of a functioning evaporator coil in a refrigeration system. The evaporator coil is responsible for absorbing heat from the indoor air, and this process involves the refrigerant flowing through the coil and evaporating, which creates a cooling effect. When the evaporator coil is operating properly, the temperature of the coil drops sufficiently to cause condensation and moisture in the air to freeze on its surface, resulting in frost.

This frost formation indicates that the coil is effectively absorbing heat and functioning as intended. It's important to note that while a certain amount of frost is normal, excessive frost build-up can indicate an issue, such as poor air flow or low refrigerant, but in its typical functioning state, frost accumulation signifies effective operation.

Other options suggest problems rather than normal functioning. Low refrigerant levels often indicate a leak or insufficient charge, which would lead to inadequate cooling. Increased room humidity can suggest that the system isn't effectively dehumidifying the air, potentially due to a malfunctioning evaporator coil. Odd odors coming from vents typically point to issues like mold, mildew, or other contaminants, which are not signs of proper function.