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AC Troubleshooting: FROZEN HVAC System? Don’t “Let it Go!”

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Last Updated on June 25, 2015


AC Troubleshooting: Why Your Air Conditioner Freezes Up and What to Do About it.

If you have children, or you’re alive on the planet, you’ve seen/heard of/know all the words to all the songs to Disney’s Frozen. In the movie “Anna, a fearless optimist, sets off on an epic journey – teaming up with rugged mountain man Kristoff and his loyal reindeer Sven – to find her sister Elsa, whose icy powers have trapped the kingdom of Arendelle in eternal winter” (so says IMDB). Yea, it’s a real nail-biter.

While you may not have a loyal reindeer, you may indeed be facing an epic journey of your own when the icy powers of your air conditioner cause an eternal winter of your evaporator coils. (Eh, come on…go with it. It was only a matter of time before a witty HVAC company took advantage of the comparison).

If you’ve ever faced a freeze up of your own, you know the symptoms:

  1. The building is too warm!
  2. There’s no air (or warm air) coming from the supply registers.
  3. The air conditioner’s filter may be wet, and you may see water leaks.
  4. If can access the unit’s evaporator coils, you’ll see that they are covered in a layer of ice.

What to do first if it happens to you:

Shut it off! Even if you can’t see the ice, you need to shut off the air conditioner immediately if you suspect it’s frozen. Don’t just turn the thermostat up so that it stops running; the unit needs to be turned off. That’s because you’re risking damage to the compressor the longer it runs with frozen coils. If the compressor goes, there’s a good chance that the entire air conditioner is DOA.

Call a certified HVAC service company. No matter what the cause of the frozen coils, the system needs to be inspected by a professional to rule out refrigerant leaks. This is not only a health and safety hazard, but in many cases you are required by law to fix them.

While you’re waiting:

Melt the ice. If you can access the coils, use a fan or blow dryer to melt the ice coating the coils. Don’t try to remove it by hand or touch the coils, which could damage them. If you can’t or don’t know how to access the coils, wait for the professionals.

Clean up the water. The leaking condensate could be missing the pan and even getting into the ducts. Use a wet vac if necessary to suction water from the ducts.

Check for air flow problems. You may have closed the registers in storage spaces or unused areas of your building to save energy, but you can’t close too many or you risk freezing the system. Make sure supply registers are open and there is no furniture or other obstacles blocking them.

What your service tech will do:

Change dirty filters and improve air flow. It may sound counter-intuitive, but your air conditioner needs warm air circulating around it to work properly. Air flow can be impeded by something as simple as a clogged filter. If your unit has not been serviced in a while and the filters are dirty, the coils can freeze.

Check the fan. If the fan motor is going, or if it’s just so dirty that the speed is reduced, the decreased air flow can cause coil freezing. The fan may just need a good cleaning, the speed may need to be adjusted, or the fan motor might need to be replaced.

Clear the condensate line and drains. When it’s working correctly, your air conditioner removes humidity from the air and condenses it into water, which travels through condensate tubing to a pan and floor drain. If there is a blockage anywhere in this drainage system, the water can freeze all the way up to the coils.

Replace faulty thermostats. If your thermostat is not working correctly, the unit may have been running continuously for some time. If it runs too long and gets too cold, the coils will eventually freeze up.

Check refrigerant levels and fix leaks if needed. When an air conditioner is leaking refrigerant, the coils become too cold and can freeze. If the refrigerant is low, your tech has to thoroughly clean the coils and check for leaks. This can be a complicated problem, because finding leaks in the coil can be difficult and time-consuming. And if there’s one leak, there’s a good chance that there are more. If your tech tells you that the refrigerant is low, make sure that he didn’t just recharge the refrigerant without finding ALL the leaks. If the tech tells you that the coils are in poor condition and likely to leak again, it may be time to start thinking about installing a new unit.

Make sure it doesn’t happen again!

The most reliable way to prevent air conditioner freeze-ups is to regularly maintain it. At least twice per year, before startup in the spring and after shut down in the fall, call in an HVAC expert to thoroughly clean and tune up your system. While any preventative maintenance plan should be tailored to fit your needs and your budget, it generally includes these tasks that prevent the problems leading to coil freezing:

  • Thoroughly clean the system, including coils and fan blades
  • Change air filters
  • Clear condensate lines and drains
  • Check operation of thermostats
  • Check refrigerant levels

If you experience frequent equipment failure and your interested in learning more about whether to fix your existing system or replace it, download our guide to Repair or Replace: A Guide to Making an Informed Choice When Your HVAC System is Down.

Should you repair or replace that broken HVAC equipment? Download the complete guide.