Why does my heat pump ice up on the coil and pipes?

Here is the answer for those people who have asked us “Why does my heat pump ice up?”

In winter it is normal for coils to ice up, however it is anything but normal for the same thing to occur in summer. Ice or frost on coils is something of a ‘catch 22′ situation as anything that restricts airflow through the inside unit will cause frost. As the frost builds, the airflow becomes more and more restricted making the condition worse and when the frost occurs on the outside pipes, damage to the compressor can occur.

Heat pumps will naturally ice-up in the winter but will periodically go into a defrost cycle, this keeps the unit running efficiently and in winter it is normal for the entire coil to be covered in frost, even a light ice. It is not normal however, for the entire unit to be encased in ice for any extended period of time.

There are a number of factors that can cause frost on your coil and/or reduced air flow:

  • Extremely dirty air filter which restricts airflow
  • Extremely dirty or clogged cooling which restricts airflow
  • The grill is obscured
  • The motor overheats and shorts the safety switch

If severely iced up, it is possible that it isn’t defrosting but there are other plausible causes:

  • Faulty defrost functions: controller, relay, thermostat or sensor
  • Sticking reversing valve
  • Faulty reversing valve solenoid coil
  • Faulty outdoor fan motor
  • Low refrigerant
  • Obscured grill
  • Outdoor coil blocked – possibly with leaves or snow drift
  • Unit sunk in ground – nowhere for ice to melt and drain off
  • Leaking gutter dripping water onto top of unit Freezing rain – causes top of unit to freeze over – once this happens the rest of the unit will also freeze over

The bottom four possible causes can be handled by the homeowner, however always bear in mind that you should never pick or scrape ice off with a sharp object; the refrigerant coils are very delicate and can be damaged easily.

Icing up can be caused by low refrigerant in the system due to a chronic leak. If the system is short on refrigerant charge, part of the coil will run very cold and ice will start to form. The solution here is to have the coil cleaned or replaced by a registered technician.

What is not normal is to see ice during the summer anywhere on the inside or outside of a heat pump. It is possible to ice-up the indoor coil, if for example, the air conditioning function is running in very cold weather or if the thermostat is turned down extremely low.