During heating mode, moisture condenses on the outdoor coil.

• A. Ice
• B. Moisture
• C. Condensation on indoor coil
• D. No condensation

Answer: (B)

When a heat pump runs in heating mode, the outdoor coil becomes the cold surface that outdoor air passes over. If the outdoor air contains moisture, and the coil’s surface temperature is below the air’s dew point but above freezing, water vapor will change to liquid and condense on the coil. That liquid water can then drain away. If the surface drops below freezing, you’d typically see frost or ice instead of liquid condensation. So the observed moisture on the outdoor coil fits the situation where humidity from the outdoor air condenses as liquid water on a cool surface. Condensation on the indoor coil would be a sign of dehumidification during cooling, not heating, and no condensation would mean either very dry air or a surface temperature above the dew point.