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Causes and Fix for Frozen Inside Air Handler Coils (Air Conditioning Unit)

Causes and Fix for Frozen Inside Air Handler Coils (Air Conditioning Unit)

by Fred Fauth (email Fred) | | July 21, 2010 | 11 Comments »

There’s really nothing worse on a hot, humid Summer day than to have your central air conditioner give out.  Unfortunately, that’s just what happened to us about three weeks ago right after our hardwood flooring installation.  The temperature in the house started climbing steadily beginning around 6:00pm, rising from a relatively cool 73 degrees up into the mid-80s.

While I’m not an air conditioner tech, I can check the basics of an air conditioning system (air filter, blown fuses, ice build-up, etc).  The skill comes in handy when you contact an HVAC technician. It’s much better to be able to tell them, “I’ve got ice built up on the inside unit” than to simply say, “It’s starting to get hot in the house.”  They’ll be able to give you some potential causes of the problem and expected costs for repair.

So I started checking what I knew to check. Step one was to pull out the air filter, which was soaking wet and was stuck on something inside the unit.  In fact, it was so stuck it wouldn’t come free and I thought continuing to struggle with it might rip it apart.  I decided to open the upper access panel that houses the interior air coil and here’s what I saw.  Problem identified.

indoor-air-conditioner-air-handler-frozen-ice

We’re no stranger to frozen outdoor air conditioner compressors. In the Winter, it’s not uncommon for an outside compressor unit to freeze up if the defrost cycle on the unit is set to run too infrequently. Freeze-up can also take place if freezing rain or snow accumulates on the fan blades, or is allowed to sit on the exterior of the unit.  Fixing an outdoor frozen heat pump can be as easy as setting the defrost cycle to run a little more frequently, which did the trick for us.

Of course, in the Summer the situation is reversed. The system extracts heat from the inside of the house and moves it outside. In this scenario, the air coils inside the interior air handler get very cold, with evaporated freon moving through them.  Air passes over these coils and most of the time, you get cool air conditioning in your home.

Cause of Ice Frozen Air Conditioner Air Handler

So what causes an interior air handler to freeze up instead of operating normally?

There are two common causes for freeze-up, and one is less expensive to fix than the other.  The first cause is a freon leak in the system. When a freon leak is present, the coils can cool unevenly with some parts of the coil staying extremely cold for a long time.  This leads to build-up of ice on the coil from the moisture extracted from humid air passing over it.  Once the ice starts to build up, it easily persists because it acts as an insulator on the coil, preventing air from passing over the coil and warming it up.

The second cause is poor air flow over the coils and fins, usually caused by an extremely dirty air filter or dirt build up on the coils or fins.  When air flow is restricted, the coils and fins become too cold leading to ice build up.

Since we had just finished that hardwood project, we figured the dust blown around in the house was probably the culprit, and at least worth checking before making a call to the technician.

How to Fix a Frozen Air Handler

The easiest way to melt the ice is to allow the fan to run without the air conditioning on for 24-48 hours.  You must let ALL the ice melt before turning the A/C back on, otherwise the problem will quickly return.

Unfortunately, we were in the middle of a terrible heat wave and didn’t want to wait 24 hours for a solution. So we used the faster method: a hair dryer and two 500-watt halogen lights. The process took 2 hours to get the air handler completely dry.

Note: You should always turn off the breaker to the HVAC unit before working on it.  Also, using a hair dryer and/or heat lights could be a fire risk if you aren’t careful.  So be careful and do this at your own risk!

It is imperative that you don’t disturb or break the coils inside the unit.  One broken coil will mean a much more expensive fix.

how-to-fix-a-frozen-air-handler

The unit dried:

defrosted-interior-air-handler-unit

We turned the unit back on and nearly instantly the cold air came rushing through the house.

In the three weeks since the event, we’ve had no recurrence.  It looks like the air filter did the trick, saving an expensive HVAC technician call and confirming that we probably do not have a freon leak. Had the unit frozen back up, we would’ve called our local air conditioning contractor to come take a look.

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11 Responses to Causes and Fix for Frozen Inside Air Handler Coils (Air Conditioning Unit)

  • Bill responds...
    July 22nd, 2010 11:36 pm

    Good article. I’m sure this well help many people out there. HVAC is a very foreign thing to most I believe.

    [Reply]

  • Patrick B responds...
    August 22nd, 2010 1:46 am

    Thanks a lot for this article/ help Thanks to you I found out what I need to do

    I will follow your recommendations
    :)

    [Reply]

  • Daytona Limos responds...
    March 31st, 2011 12:49 am

    Thanks for the info our shop AC froze up today and it has never done that before.

    [Reply]

  • Kate the Great responds...
    July 9th, 2011 1:27 pm

    Fantastic info – what did you need to change/clean to stop the ice from forming again? The usual in-ceiling filters, or do you have a whole-house filter or a filter-drier?

    [Reply]

  • Fred responds...
    July 9th, 2011 7:51 pm

    Kate, we just replaced the whole house filter and kept an eye on it. We didn’t end up with a refreezing problem. If it keeps occurring it can be caused by low freon, but I would definitely replace the filter first.

    [Reply]

  • Megan responds...
    August 12th, 2011 8:02 pm

    Thank you! We’ve been having this issue off and on for a year, each time just defrosting it and replacing the filter. You’re the first person who has put pertinent info out there about this problem. Thank you so much! Looks like now we can look into getting our leak fixed… :)

    [Reply]

  • Andre responds...
    August 20th, 2011 4:41 pm

    Thanks for the info. My filter was really dirty and my unit was frozen just like the one in the photo. I’ll cross my fingers, but the advice seems dead on. There must be a lot of techs wishing you had kept this info. to yourself, but us financially challenged people appreciate it. Thanks again.

    [Reply]

  • Tammy responds...
    May 3rd, 2012 6:55 pm

    My unit on the inside is sometimes leaking on the sides. Right now I have bowls there to catch the water. It was leaking last summer then stopped during the winter when the a/c wasnt working as much but I just noticed the other day that it’s leaking again but not all the time..Do u know what’s the problem & how can I fix it before it starts to get really hot & leaks alot.Thank you..

    [Reply]

  • eve responds...
    June 12th, 2012 2:12 pm

    Hello, if the freon is low how can you tell and fix it? ours froze just that way out of the blue and my filter wasn’t that dirty that why i’m thinking it may be freon, is that very costly to put in?

    [Reply]

    Fred Reply:

    You will need to have a licensed HVAC Technician test it. Usually house calls run between $100-$120 to check things out. Testing freon requires special tools and techniques. Short of buying a testing kit and getting a book (which will require time and money), I would go with the pro for something like this.

    [Reply]

  • RICK responds...
    July 3rd, 2014 5:54 pm

    THANKS, FRED! U YOU SAVED MEA HOLIDAY SERVICE CALL: LATE AFTERNOON JUL 4 14

    [Reply]





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