Steam is coming out of my outdoor unit


When new heat pump owners first think they see steam coming from their heat pump, they are sure the outdoor fan is burning up. This feeling is further enhanced when the motor also stops running.

Don't worry, this is a good thing.  It is your unit going into its defrost mode.  It happens regularly during the heating season. The outdoor coils tend to frost or ice-up during the winter. This causes the unit to lose efficiency. By regularly defrosting itself, the heat pump runs more efficiently.

When the unit goes into defrost, several things happen. First, the outdoor fan stops running. This helps build up more heat to melt the ice. Also the reversing valve shifts from the heating mode to the air conditioning mode. Temporarily making the outdoor unit a condenser, the hot refrigerant passing through the coils accomplishes the necessary defrosting. At the same time, the supplemental heat is energized to temper the otherwise cold air that would be blowing into the house.

At first glance this seems bizarre to say the least (running the air conditioning and heating at the same time) but it usually is only for a few minutes at a time and only when needed.  If your unit is constantly going into defrost, this could indicate a problem.

Below is a list of possible causes. Items in blue can be addressed or fixed by the homeowner. Those in red usually require a service call.


  • Outdoor coil blocked-possibly with leaves


  • Defective defrost control

  • Defective defrost sensors or thermostats

  • Defective outdoor fan motor

  • Low refrigerant charge or a restriction


Hope this has been of some assistance, however they are just rough guidelines and not all possible conditions are covered.




The company You Choose To Install and Service Your System Will Determine The Degree of Comfortand Satisfaction You Enjoy.

Excerpts of the preceding information has been compiled by Hannabery HVAC, which has graciously permitted us to include them on this web site as a service for all homeowners.

These "Common HVAC Problems" are provided FREE and as a consequence Climatemakers does not assume any liability resulting from any information we provide. In all cases where there is any possibility of injury, consequential damage, direct damage to your equipment or when recommended by the equipment manufacturer, your system should be repaired, inspected or maintained by a qualified technician.

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