What Is “Defrost Mode” In My Heat Pump System

Heat pumps offer the most efficient way to provide heating and cooling in many applications. It is an all-in-one heating and air-conditioning system that works year-round to keep you comfortable.

Heat pump operation for Asheville Residents

Heat moves naturally from higher to lower temperatures, however, heat pumps are able to force the heat to move in the opposite direction. During the heating cycle a heat pump uses heat and humidity from the outside air, to heat your home. During warmer months, it works like a normal air-conditioner, removing heat from inside your home and transferring it outside. During heat mode and outdoor ambient temperatures are very cold, humidity in the air causes moisture to freeze on the outdoor section of the system. The system recognizes ice has begun to form and automatically goes into a defrost cycle.

Why does a heat pump defrost?

When the excess moisture begins to freeze up, it can potentially restrict air flow across the outdoor heat exchanger which is the outdoor coil. Reduced air flow can lower the efficiency of the system or eventually damage components. A heat pump automatically defrosts itself to prevent ice accumulation and maintain equipment efficiency.

When the heat pump goes into defrost cycle, a reversing valve inside the unit, which controls the flow of refrigerant, shifts. When this valve shifts, you may hear a hissing sound which lasts a few seconds. Steam rising from the outdoor equipment is common and an indication of proper operation.

What is the buzzing noise at my heat pump?

During the defrost cycle, you may hear a buzzing noise or a low humming and the compressor may seem louder than normal. You may also see the fan is not turning and hot air is emanating from the unit.

After the unit cycles and refrigerant levels equalize, the unit will return to normal operation. All of this is completely normal as the unit is in defrost mode.

For optimum heat pump operation in Asheville, NC

If you own a heat pump system here are several recommendations:

  • Avoid constantly adjusting your thermostat. Set it to one temperature and leave it.
  • During the heating season, avoid setting the thermostat below 65º.
  • On a regular basis, clear the outdoor unit from debris, limbs, leaves, or snow.
  • Keep shrubs and landscaping at least 18-inches away from your outdoor unit.
  • We recommend scheduling a preventative maintenance visit at least once a year to maintain optimum efficiency.

If you have further questions or concerns that your heat pump is not operating properly, please contact the experts at Sheer Comfort Heating & Air Conditioning.