What Causes an Air Conditioner to Freeze Up?

airflow design

Does the air flowing from your supply registers feel warm and weak? If so, the indoor evaporator coil is the first place to check. Ice can also form on the refrigerant line connected to the outdoor unit, so check there as well. If you see ice buildup or puddles on the ground in either location, you’ve got a frozen air conditioner on your hands. Learn what causes an AC unit to freeze, what to do if you discover this problem, and how to prevent it in the future.

Why Air Conditioners Freeze Up

It’s strange to think that your air conditioning unit could freeze in the middle of summer, but it’s a fairly common occurrence here in Florida. Here are the most common reasons why air conditioners ice up:

  • Refrigerant problems: An undercharged refrigerant system means the coolant level is too low. This can happen due to improper charging during AC installation or because a leak has developed over time. Either way, low refrigerant causes the evaporator coil to become too cold. As a result, moisture in the surrounding air freezes and accumulates on the coil.
  • Clogged air filter: This is a primary cause of poor airflow. After all, when the filter becomes too dirty, less warm air is able to blow across the evaporator coil for cooling. It’s important to keep airflow high enough so the evaporator coil doesn’t freeze.
  • Inadequate fan speed: The blower motor must operate fast enough to create high-velocity airflow over the evaporator coil. A low fan speed or insufficient power is another cause of poor airflow, leading to a frozen air conditioning unit.
  • Closed or blocked registers: It may be tempting to shut the air registers in unused rooms, but if you close more than 20 percent of the air vents around your home, you could unintentionally restrict airflow and cause the AC to freeze up.
  • The constant operation, especially at night: If the air conditioner never cycles off, the evaporator coil is liable to freeze. The risk goes up if you run your AC constantly when it’s cold outside.
  • Dusty evaporator coil: A thick layer of dust inhibits heat transfer between the warm air blowing over the evaporator coil and the cold refrigerant flowing through it. If the cold can’t escape, the coil could potentially freeze over.

What to Do if Your AC Freezes Up

Never ignore a frozen air conditioner. Running it with ice on the evaporator coil or refrigerant line could waste money and damage the compressor. Shut off the AC unit and follow these steps to melt the ice:

  • Turn on the HVAC fan only to circulate air over the ice. To speed up the process, aim a hairdryer directly at the evaporator coil.
  • Consider opening up the ductwork to suction out water with a wet-dry shop vac as the ice melts.
  • Only turn the AC back on after the ice has melted completely. The unit should begin cooling your home immediately.

How to Prevent Ice on the Air Conditioner

If you don’t address the cause, your air conditioner will freeze again before long. Here’s how to prevent ice from returning:

  • Check your HVAC air filter once a month and change it when it appears dirty.
  • Keep at least 80 percent of your supply registers open at all times. Also, make sure rugs, curtains, and furniture don’t block any vents.
  • Avoid running your AC when it’s below 60 degrees outside. Instead, open the windows to enjoy free cooling.
  • Don’t set your thermostat lower than 72 degrees in the summer.
  • Inspect the condensate pan weekly for blockages. Apply algaecide treatment when necessary to clear the drain line.
  • Schedule AC maintenance once or twice a year. During the visit, your technician can check the refrigerant level, repair any leaks, and recharge the system as needed. You can also ask to have the fan speed increased, if necessary.

Schedule Air Conditioning Repair in Central Florida

If your AC has frozen up or is having other problems, turn to Certified Climate Control. Our technicians have years of experience maintaining and repairing air conditioners and other HVAC equipment. We also retain an A+ rating with the BBB and have earned the Super Service Award nine years in a row. Contact us today to schedule air conditioning services in Orange, Seminole, or Volusia County, FL.