During the heating cycle of a heat pump, moisture from the outdoor air will condense on the outdoor coil.

• A. Moisture
• B. Ice
• C. Humid air
• D. Condensation on indoor coil

Answer: (A)

When a heat pump is in heating mode, the outdoor coil acts as the evaporator and becomes cold. As outdoor air passes over that cold coil, water vapor in the air can reach its dew point and condense into liquid water on the coil. That’s why moisture appears on the outdoor unit during heating. If temperatures drop below freezing, that condensed moisture can freeze and form ice or frost, but the process described in the question is condensation (liquid water). The other options don’t fit because humid air isn’t condensing on the surface, and ice would only form if the surface were cold enough to freeze the condensate, while condensation on the indoor coil would describe the cooling mode, not heating.