Got a Frozen Evaporator Coil? Don’t Panic, Do This.
Key takeaways:
• If the indoor evaporator coil, part of your heat pump or air conditioner system, is frozen, turn off the system at the thermostat but leave the fan set to ON to help the coil thaw out.
• Check your air filter and change it if it’s clogged or dirty.
• Call for HVAC assessment and repair.
By Anne Fonda
The indoor evaporator coil is a crucial component of your air conditioning or heat pump system.
"Your evaporator coil, cased coil or furnace coil is key to ensuring your home is comfortable in all seasons, especially the warmer summers. It helps to absorb heat and keep your home cool."
-Sean Goddard, Product Manager, Coils & Indoor Air Quality
With proper airflow and regular maintenance, you may never have an issue with it. However, as an HVAC system ages, the evaporator coil can be susceptible to problems, the biggest of which is freezing over.
How to tell if an evaporator coil is frozen
Frozen evaporator coil symptoms can include:
- Visible icing on the evaporator coil or outside cabinet
- Visible icing on the outside refrigerant lines
- AC not blowing cold air/blowing warm air
- Puddles of water underneath the air handler or coil cabinet if the coil is thawing out
The blowing warm air and the puddles of water can be indications of other problems, but an HVAC technician can help sort things out.
If you have a heat pump system and the outdoor unit appears to be icing up in cold weather, that’s normal. The heat pump defrost cycle should kick in, thaw things out, and then return to normal heating mode. If the defrost cycle lasts longer and longer, and ice starts to cover the unit, call for repair. You may have a bad defrost control board. Replacing it is an easy fix.
What causes frozen evaporator coils?
The most common cause for a frozen evaporator coil is improper airflow, but there are a few other causes. Let’s take a look.
#1: Dirty or clogged air filter
A clogged filter restricts airflow. Restricted airflow can cause the evaporator coil to freeze. You can help prevent this by changing the air filter every 30-90 days.
Read more about air filter replacement.
#2: Dirty evaporator coil
A dirty evaporator coil also restricts airflow, since the coil is coated in a layer of dust and grime. A dirty coil can be a direct result of a dirty or clogged filter.
"Small investments in your HVAC system’s health help prevent larger issues when you least expect or want them!"
-Sean Goddard, Product Manager, Coils & Indoor Air Quality
Prevent a dirty coil by scheduling regular HVAC maintenance. A technician can check the coil and clean it if needed.
#3: Blocked return vents
We keep going on about airflow, but it’s really important. Blocked return vents can restrict airflow. Make sure that furniture, drapes, or other items are not blocking them.
#4: Faulty or broken thermostat
A broken thermostat can also cause a frozen evaporator coil. If the coil is only frozen in the morning (it froze up overnight), this could indicate that the thermostat is to blame. If the thermostat isn’t telling the cooling system to shut down as overnight temperatures fall, the constant running could cause the coil temperature to drop below freezing.
#5: Refrigerant leak/low refrigerant
Lastly, a refrigerant leak can cause a frozen evaporator coil. A refrigerant leak can be caused by vibration, years of wear and tear, or a frozen evaporator coil. An improper refrigerant charge at installation can also result in low refrigerant levels, causing an evaporator coil to freeze up. An HVAC technician will perform one or more tests to confirm a refrigerant leak.
How to fix a frozen evaporator coil
As a homeowner, you shouldn’t attempt HVAC repair on your own. But there are a few things you can do while you wait for an HVAC technician.
#1: Thaw the coil
First, as mentioned above, turn the cooling system off at the thermostat. Running the AC unit or heat pump with a frozen coil can do major damage to the system.
Set the fan to ON to help speed the thawing process. An HVAC technician cannot evaluate the coil and refrigerant lines until the coil is thawed. If it’s still frozen when they arrive, they will either leave and come back or wait there, on the clock, for the coil to thaw.
DO NOT CHIP AWAY AT THE ICE.
#2: Be prepared for dripping
As the coil thaws, it will drip. If it is fully encased in ice rather than just a little frost, you can expect it to release 1-2 gallons of water as the ice melts. If the indoor coil is on a concrete floor in the basement, you can put old beach towels down to soak up the moisture. If the evaporator coil is in your attic, you may want to place a plastic tarp, tub, or bucket to catch the dripping water.
#3: Check the filter
One of the most common causes for a frozen evaporator coil is poor airflow. This can include a clogged filter. Change the filter if it’s dirty. Make sure supply registers and return air vents aren’t blocked by furniture or drapes.
#4: Call for HVAC repair
Next, call to schedule an HVAC repair call. Remember, the coil must thaw before the HVAC technician can assess the situation. They’ll want to check for a dirty coil, a possible refrigerant leak, and more. They can’t do that if the coil looks like a block of ice.
#5: The possible fix
If the AC coil froze because the evaporator coil is dirty, the technician will clean it and test the system. If they determined there is a refrigerant leak, the conversation shifts. Some leaks are easily repairable by brazing the refrigerant lines. But if the leak is in the indoor coil itself, you may need evaporator coil replacement.
Replacing the evaporator coil is labor-intensive and pricey, so you will need to decide if coil replacement or unit/system replacement is the more cost-effective option. For a repair (or replacement) of this magnitude, you may want to get a second opinion, or even a third.
Get help now
Contact your local American Standard dealer to assess the problem and propose a fix. They’ll run any necessary diagnostics to come up with a solution – possibly two or more options, one a short-term fix and another a long-term solution.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Sean Goddard, Product Manager, Coils & Indoor Air Quality, and Kimberly Sexton, Senior Systems Engineer
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