A heat pump operates similarly to an air conditioner: it circulates refrigerant between indoor and outdoor units, absorbing heat from inside a house and then releasing it to the outside. The difference between a heat pump and an air conditioner, however, is that a heat pump can change the direction it moves refrigerant. When the refrigerant cycles in the reverse direction, the heat pump absorbs heat from the outside and releases it to the inside, providing warmth.
It’s easy to switch a heat pump from heating to cooling when warmer weather arrives: you just set the thermostat to “cool” and adjust the temperature. The heat pump will take it from there. However, you may find yourself at the start of the season with a heat pump that won’t start cooling. Either it stays in heating mode or it only sends out room temperature air. What’s happening?