Understanding the Defrost Cycle on Your Heat Pump

The defrost cycle of a heat pump system is crucial to maintaining its optimal performance and for ensuring the longevity of your heating and cooling investment.

When a heat pump is performing in its heat cycle it is typically doing so in the cooler winter months. When the ambient air temperature outside of your home is cool and the relative humidity is high, it can carry more water vapor than normal. This set ups a condition wherein frost might form on the surface of the much colder outdoor coil. If left unattended, this frost covering will interfere with the optimal operation of the heat pump, which costs you money. To correct this occurrence, the auto defrost cycle on your heat pump becomes activated to remove the frost.

Do you see smoke wafting from the outdoor coil during the defrost cycle? Your heat pump isn’t actually smoking. In truth, it is actually steaming. During the defrost cycle, frost is rapidly converted back to liquid or even to water’s gaseous state which is steam. Many folks can easily confuse steam as smoke (especially when it is cold outside) and become concerned there is a more problematic issue occurring. This is rarely the case and visible steam during the defrost cycle is perfectly normal. However, there are warning signs you should be observant of, especially the presence of ice.

Defrost cycles are preventative in design in that they prevent frost coating from forming into more destructive ice encasements. If the defrost cycle is not performing well enough at removing frost, then ice can cover the outdoor coil and spread outward to the top and sides of the unit and eventually the entire unit can be encased in ice. Ice can then crush components like outdoor coils thus causing refrigerant leaks. Ice can also prohibit moving parts like fan blades from functioning and thus burning out the fan motor. Some units can be completely covered in ice and can become unsalvageable so it is important to visually inspect your outdoor heat pump components regularly for signs of persistent ice, especially when humidity levels have been high.

If you do notice your heat pump is icing up during winter use, it could be that the defrost cycle is underperforming or not performing at all. Other issues may also be at play. Here are some possible causes:

• Defective defrost control
• Defective defrost thermostat
• Defective defrost sensor
• Defective defrost relay
• Defective reversing valve
• Defective fan motor
• Low refrigerant
• Snow or leaves blocking/covering the outdoor coil
• Outdoor coil is below ground level
• Outside water source is leaking onto outdoor coil (hose spigot or gutter)
• Snow or freezing rain accumulation on outdoor coil

Call Boyd Service Company at (501) 626-8506 today to help diagnose any icing you may notice before damage to your heat pump can occur. We’re here to help!