Common Causes of Heat Pump Short Cycling

HVAC Logo IconBy Tom MoorOctober 31, 2023
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HVAC technician checking refrigerant level of HVAC system

Is your heat pump exhibiting strange behaviors? One of the most common heat pump issues is short cycling. Heat pump short cycling occurs when your system cycles on and off too frequently without reaching the set temperature on your thermostat.

A short cycling heat pump can cause serious damage to your unit and should be inspected by a professional HVAC contractor as soon as possible. Keep reading as explains what short cycling is and the common causes of it.

What Exactly Is Heat Pump Short Cycling?

When a heat pump short cycles, it starts a cycle, runs for a few minutes, and stops prematurely – only to start another cycle a few minutes later.

A properly functioning heat pump typically only runs a few cycles per hour, so if you notice that the system is running significantly more cycles, it’s likely over cycling. Heat pump short cycling can cause several issues including poor temperature control, high energy bills, frequent repairs, and increased system wear and tear.

Common Causes of a Short Cycling Heat Pump

Some of the most common symptoms behind a heat pump cycling on and off include:

A Clogged or Dirty Air Filter

Neglecting to swap out your furnace filter every couple of months can have grave consequences. It may cause high energy bills, increased system wear and tear, and, eventually, short cycling. Clogged air filters restrict airflow into your heat pump system which causes it to work harder. It can even trigger your heat pump fan motor or compressor to overheat, forcing your system to shut down as a safety precaution, leading to a short cycling heat pump.

If you notice short cycling, the HVAC filter is a good place to start looking. It’s good practice to replace your filter every 2-3 months, or according to the manufacturer’s recommendations.

An Incorrectly Sized Heat Pump Unit

Size matters when it comes to your heating and cooling equipment. An incorrectly sized heat pump system, whether too small or too big, can lead to a host of problems including short cycling. During the HVAC buying and installation phase, ensure that your HVAC technician performs a Manual J calculation of your home to determine the correct size heat pump.

A heat pump that’s too small may struggle to effectively heat or cool your home, possibly leading to overheating and short cycling issues. Meanwhile, a system that’s too large for your space will reach the set temperature too quickly, leading to frequent cycling that can cause premature wear and tear and high energy bills.

A Refrigerant Leak

Refrigerant plays a critical role in the proper operation of your heat pump. It removes warm air inside homes during the warmer months for cooling and extracts heat from the outside air during the colder months to provide warmth. When your heat pump springs a refrigerant leak, it causes your system to work harder to heat and cool your home which can cause parts to malfunction or the system to overheat, leading to heat pump short cycling. Refrigerants should only be handled by a qualified HVAC technician who is trained to work with this liquid chemical.

Frozen Evaporator Coil

Another common cause of heat pump short cycling is a frozen evaporator coil. While operating in cooling mode, your heat pump’s evaporator coil uses refrigerant to extract warm air and excess humidity to effectively cool your home. The evaporator coil can freeze up over time due to a malfunctioning blower motor, a low refrigerant level, and restricted airflow from a clogged HVAC air filter. A frozen evaporator coil may cause your heat pump to overheat, leading to potential short cycling.

To unfreeze an evaporator coil using DIY methods, turn the heat pump system off and allow the evaporator coil to thaw for 24 hours. You can quicken the process by using a hair dryer, but don’t use any sharp objects to chip away at the ice which can lead to damage. If the freezing comes back, contact a reputable HVAC contractor to inspect the system.

Electrical Issues

Electrical problems can lead to various heat pump issues, one of which is short cycling. Issues with your heat pump’s electrical system, such as loose or corroded connections, can result in your heat pump intermittently shutting off throughout the day, causing short cycling. If you suspect that electrical issues are behind your short cycling heat pump, contact a professional HVAC contractor or a licensed electrician to inspect the system and make the appropriate repair.

Regular Maintenance Can Prevent Heat Pump Short Cycling

The best way to avoid unwanted HVAC short cycling is through regular HVAC maintenance. If you use your heat pump for both heating and cooling, invest in two heat pump tune-ups per year; once before the heating season and again before the cooling season.

During a heat pump tune-up, your technician will inspect, calibrate, and clean all necessary components. They will also identify any issues such as an electrical problem or a clogged air filter that can eventually lead to heat pump short cycling.

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