While your air conditioner produces cold air, it should not freeze up. Rather, the evaporator coil inside your home should absorb heat and condense moisture from the air circulating through the system. When an AC freezes up either inside your home or at the unit outside, it can no longer efficiently move heat and indicates that you’ve got a problem that must be identified and solved. Consider these 11 common culprits of air conditioners freezing up.
1. The Air Filter Is Clogged
The first thing to check any time you have an issue with your air conditioner is your air filter. Without proper airflow, your system can experience various symptoms, including system freezes. The filter gets clogged when left in place for too long because it’s doing the job of keeping contaminants out of the system. When too little air moves through the system, the evaporator coil will get too cold and will start to freeze.
Check your filter monthly so that you quickly identify when it becomes dirty and needs replacing. Under normal conditions, the common 1- and 2-inch filter needs replacing every 30 to 90 days. If your system uses larger filters, it may last several months to a year depending on the size, your home’s air quality, and the filter’s construction.
2. Refrigerant Leak
The system cools your home by regulating the refrigerant’s pressure at the evaporator and condensing coils. Whenever the refrigerant pressure decreases, the refrigerant gets cold. A leak in the system allows the pressure to drop too much or at an unexpected location. This is why you may see freezes on the refrigerant lines or at the evaporator coil, the compressor, or the accumulator.
Beyond freezing the system, a refrigerant leak will also put tremendous strain on the compressor, causing it to wear out prematurely, which is an expensive repair if not a full system replacement. A technician will check the refrigerant level during routine maintenance before it causes a freezing issue.
3. Restricted Airflow
Beyond the air filter, your system’s airflow can become restricted in several areas. The most common are the supply and return vents. First, check to make sure that every supply vent is open, even in rooms where you don’t spend a lot of time. It might not initially make sense, but this is critical for circulating cool air throughout your home. Check that all vents have the proper clearance to allow air to flow about 6 inches above the vent unrestricted.
Check your cool air returns as well, ensuring they are clean and unobstructed. How much clearance these vents need depends on their size, so check with the technician at your next maintenance appointment.
4. Dirty or Damaged Coils
Dust and dirt are no friend to the coils in your air conditioner. As the system runs, the evaporator coil will become wet from condensed moisture on the cold coil. This combines with dust and dirt on the coil to form a type of insulation that inhibits proper heat transfer between the air and refrigerant. The result is that the coil gets very cold without allowing heat to pass into the refrigerant, causing ice to form on the coil.
Additionally, the coil has fins that help with heat diffusion but are easily damaged. When these are damaged, they often flatten and prevent air from moving easily over the coil. This causes the same kind of issue as other airflow restrictions, including freezes in the system.
5. Faulty Thermostat
The thermostat is the brain that controls when the air conditioner runs a cooling cycle and when it turns off. Thermostats have an anticipated life of about 10 to 15 years. When it ages, it can fail to register the temperature properly, causing the system to run longer. If you have an air conditioner with a modulating-stage compressor, the compressor could run at too high of a capacity, which can cause freezes.
6. Malfunctioning Control Board
While the thermostat controls the cooling cycle, the control board controls how the system runs. If the control board is malfunctioning, it may not register temperatures, pressure, and electrical signals properly. This can result in the system running stronger and longer than is needed, preventing the system from absorbing enough heat to keep it from freezing.
7. Bad Circulating Fan
The circulating fan is often shared by the air conditioner and your heating system. It’s responsible for drawing in air from around your home, pulling it through the system, and then pushing it back into your home. As it wears, it can stop spinning as quickly as it should or may not spin altogether, failing to circulate enough air to make the system run properly. A technician will check and clean the circulating fan during routine AC maintenance, and they’ll tighten the fan mounting bolts that loosen from operational vibration.
8. Insufficient Supply or Return Vents
If you’ve recently updated your air conditioner, you could have an issue with not enough supply or return vents. On the one hand, you’ll have excess cold air build up in the system. On the other, you’ll starve the system of the air needed to cool your home effectively. Both can result in the evaporator coil getting too cold and freezing.
9. Oversized Unit
Air conditioner size is rated using BTUs, or British thermal units. This considers how much heat the system can absorb and transfer per solid hour of operation. More BTU isn’t always good, causing a system to freeze and short cycle if it’s oversized. A technician should perform an HVAC load calculation to determine how much cooling capacity your home needs, with the Manual J calculation being the standard in most areas.
10. A System That’s Ready to Retire
Most property owners around the area can expect an air conditioner to last 10 to 15 years when properly maintained. As air conditioners get older, they have components that fail, dirt collected internally, and loosening or worn wires. The result is that the system may not be receiving the proper airflow, transferring heat properly, or having enough refrigerant, all potentially causing freezes.
11. Excessive Home Humidity
Humidity is always a challenge in cooling your home. On the experiential side, it makes your home less comfortable due to the mugginess. On the operational side, it makes your system strain because humid air holds more heat and is harder to cool. Higher humidity also means more condensation forming on the indoor coil, further exacerbating the insulating effect. If you find that your home remains above 50% relative humidity while your AC runs, you may want to consider adding whole-house dehumidification.
People around San Antonio have trusted the combination of modern knowledge and old-fashioned ethics offered by Cowboys Air Conditioning & Heating since 1985. Our expert technicians provide heating and AC maintenance, repair, and installation combined with indoor air quality solutions, home sealing and insulation services, and ductwork cleaning, sealing, and repair. Call to schedule an AC repair or maintenance visit with one of our highly-rated technicians today.
