While some ice is normal something is wrong if the entire unit is encased in ice and frozen solid.
Air must pass between the fins of the outdoor unit if the condensing fan motor cannot pull air in and out through the fins then there is a problem.
Heat pumps are becoming much more efficient every year but each unit as a set low temperature which they can still pull cold air from a home and not freeze up.
To keep this from happening a heat pump must go into defrost mode when it becomes too cold. Defrost mode switches the heat pump into air conditioning mode (yes air conditioning) for a short time until it unfreezes itself and can go back into heat mode.
Defrost mode usually last only 10-15 minutes. While a unit is in defrost mode supplemental heat, usually heat strips, kick on to keep the air warm.
Heat strips are basically large elements that work like a big space heater by using electricity to heat the elements up and send out heat. Heating a home with heat strips is terribly inefficient and not designed to be on for long periods. If they are used a lot then it will show up on a electricity bill.
What to Check for a Heat Pump Freezing Up
- Check if the air filter is dirty or replace it, air flow is a must for a heat pump to work correctly.
- Does any air blow from the vent at all? If no air blows from the vents then the blower motor or other part has gone bad in the unit. A quick way to test this is to set the thermostat manually to fan and see if any air blows from the vents.
- When a heat pump is running the large fan on the outdoor unit (called the condensing fan motor) should kick on at some point and blow air out through the fins.
- Check the fins for any debris that may be blocking air from passing though such as dirt or leaves.
A water hose can be used to melt the ice buildup if needed, but don’t use salt or any other abrasive as this will only cause corrosion of the unit.
If the unit is frozen solid but still blowing hot air more than likely the heat strips have activated and are heating the home. This will quickly run up a electricity bill and be expensive if done long term. A day or two may not be that bad but weeks or a whole month of heating this way will definitely be noticeable. Call out a repair man as soon as possible.