Why is Steam coming from my AC?

We get calls mostly from new heat pump owners at the beginning of each heating season. Sometimes they mistake the steam they are seeing for smoke. Some even thinking their outdoor fan motor burned-up, because when this is happening the fan actually stops running even though the compressor continues running, sometimes making a louder than normal sound.

This is actually your heat pump in “Defrost Mode”. It happens regularly during the heating season. The outdoor coils tend to ice-up during the winter – especially in moist conditions as we have here in Florida with the humidity, causing the unit to loose efficiency. By regularly defrosting itself; keeping the outdoor coil clear for proper airflow, the heat pump runs more efficiently.

When the unit does go into the defrost mode, a couple of things happen. First, the outdoor fan motor stops running. This helps build-up more pressure and heat to melt the ice. Also the reversing valve shifts from the heating mode to the air conditioning mode. That’s right, you are actually running the air conditioner. By making the outdoor unit the condenser, the warm refrigerant gas passing through the coils accomplishes the defrosting. Lastly, the supplemental heat at the indoor unit is energized to offset the now, cold air blowing in the house.

It usually only happens for a few minutes at a time, and only as needed.

Now, your heat pump should only go into the defrost mode periodically, except for severe weather conditions (snow, rain, sleet). If your unit is constantly going into defrost, this may indicate a problem.

Below is a list of possible causes. Items in red usually require a service call. Items in green however can be addressed, some even fixed by the homeowner.

  • Bad defrost control
  • Bad defrost sensor or thermostat
  • Bad outdoor fan motor
  • Low charge or restriction
  • Outdoor coil blocked – possibly with leaves or ice

Don’t hesitate to give us a call if you feel you need service.

Brown’s Arctic Air, 352-728-4990.

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