Short-cycling is when an HVAC system terminates its heating or cooling cycle prematurely. In many instances, it will attempt to start the cycle every few minutes. Beyond the annoyance, short-cycling wears out your HVAC system more quickly, increases your system’s energy consumption, and leaves your home uncomfortable. Discover ten common reasons that could make your HVAC system short-cycle, what you can do to prevent the problem, and how to deal with it if it happens.
1. Clogged Air Filter
Many HVAC problems can be traced back to clogged air filters, which restrict airflow through the system relatively quickly if neglected. When they clog, the system can overheat, shut down, and then restart quickly. Prevention is simple: change your filter regularly, usually every 30 to 90 days for the common 1- and 2-inch filters. Stay on top of your filter by checking it monthly, and extend its life span by gently vacuuming it whenever you check it.
2. Oversized HVAC system
Air conditioners and heating systems come in different sizes that refer to their heating and cooling capacity. Each home needs the proper size system for its needs, determined by the home’s square footage, construction, environment, and number of occupants. When the system is oversized, its temperature gets too cold or too hot, shutting it down. If this is an issue, you’ll likely notice it shortly after a new installation.
3. AC or Heat Pump Refrigerant Leak
Air conditioners and heat pumps rely on refrigerant to absorb heat in one place and transfer it to another. In either case, the system must regulate the refrigerant’s pressure, dropping it to make it cold and then increasing it to make it warm. When there’s a leak, it can strain the compressor and cause a freeze in the system. System freezes can cause system short-cycling, which tends to prevent further damage.
4. Electrical Problems
All HVAC equipment relies on electricity to heat or cool your home, even if it also burns fuel. Each system has a complex network of wiring, connections, and electrical components. Components like contactors and capacitors can go bad, which may cause short-cycling. Further, the system’s vibration can loosen electrical connections, making unstable electrical flow through the circuit, also potentially causing short-cycling.
5. Improper Installation
How HVAC equipment is installed makes a big difference in how it will run, with some studies showing that as many as 90% of systems are installed incorrectly. This is part of why manufacturers typically require professional installation to maintain the factory warranty. However, even with professional installation, mistakes can happen. Some of these mistakes can affect airflow through the system, the system’s refrigerant charge, or how efficiently fuel burns. Any of these can cause the system to short-cycle, which you’ll likely notice soon after installation.
6. Restricted Airflow
HVAC systems simply cannot run properly without adequate air moving through them. Whenever there’s a restriction in your system’s airflow, it will add strain, increase wear and tear, and reduce your system’s efficiency. If the restriction is significant enough, it will cause the system to short-cycle or fail to start altogether.
Beyond a clogged air filter, there are many causes for restricted airflow. These causes may include a malfunctioning circulating fan, closed or blocked vents, and neglected maintenance, to name a few. If the air filter isn’t the problem, diagnosing this issue requires a cooling and heating repair expert.
7. Misplaced Thermostat
A thermostat acts as the brain of your HVAC system, telling it when to start and stop heating or cooling cycles. It does this by registering the temperature of the air around it. This is why placing it correctly is crucial for getting your system to run properly.
When it’s placed too close to a supply vent, it may register the temperature as too warm or too cool, depending on the cycle running. The air coming from the supply vents is warmer or cooler than your desired temperature. This prevents the thermostat from bringing the temperature throughout the entire house to the set level.
Manufacturers recommend placing the thermostat on an interior wall in a hallway that does not receive direct sunlight. Hallways are generally recommended because they usually do not have supply vents, relying instead on air circulation for their temperature regulation.
8. Failing Compressor
An AC or heat pump compressor regulates the high-pressure refrigerant in the system. The lower-pressure refrigerant flows in and the compressor forces it into a smaller space, compressing it and increasing the pressure and temperature. This process allows the system to expel the heat the AC absorbs. It goes either into your home during a cooling cycle or outside during a heating cycle.
A failing compressor may not create enough pressure to effectively transfer the heat, leaving the refrigerant too warm throughout the system. Eventually, this may cause short-cycling as the system’s safety sensors trigger premature cycle termination.
9. Faulty Low-Pressure or Upper-Limit Switch
Every HVAC system has inherent risks, but most are mitigated through the use of sensors to shut it down when there’s a problem. In air conditioners and heat pumps, the low-pressure switch monitors the low-side pressure, shutting it down if it gets too low. Gas furnaces have an upper-limit switch, which monitors the temperature in the system to prevent overheating.
Either of these sensors, in addition to several others, can go bad and register incorrect readings. When this happens, it may shut the system down errantly, only to quickly restart again.
10. Aging or Faulty Thermostat
Digital thermostats have an expected life span of about 10 to 15 years. As the thermostat ages, the ambient room temperature sensors may stop reading accurately. Further, these sensors may become faulty prematurely, causing short cycling.
Preventing and Dealing With HVAC Short-Cycling
As they say, an ounce of prevention is worth a pound of solution. Maintaining your system is the best way to prevent short cycling. This includes replacing your air filter and getting routine professional maintenance. Maintenance visits should occur twice per year, once in the spring to service your air conditioner and once in the fall for your heating system.
Even with proper maintenance, your system may still experience short-cycling. If this happens, start by looking for easy solutions first. Change the air filter, check for closed or blocked vents, and ensure your outside unit is clear. For AC or heat pump short cycling, check to see if there’s any obvious ice buildup on any visible part of the system.
If the simple fixes don’t work, then call to schedule a professional technician to troubleshoot the problem. Any DIY attempt at a fix that requires replacing parts may void your factory warranty. Further, it’s easy to waste a lot of money and time trying to solve the issue without testing the system to find the underlying problem.
For nearly 30 years, homeowners around Omaha have trusted the professionals at John Henry's Plumbing, Heating, Air, and Electrical to keep their homes comfortable. Our experienced team provides award-winning heating and cooling maintenance, repair, and installation along with a wide range of residential electrical and plumbing services. Call today to schedule an HVAC maintenance or repair visit with one of our experienced technicians.
