Why is my mini split freezing up? Common causes and fixes

Mini splits are great for keeping your home comfy year-round, but finding your indoor unit covered in ice is definitely a head-scratcher. If your mini split’s freezing up, you’re probably asking yourself what’s going on and how to sort it out. Let’s go over some common reasons for freeze-ups and some easy fixes you can try at home.

The tips in this article might not fit your exact appliance model. We aim to give handy advice for all sorts of DIY fixes, but different models and setups can change the steps, error codes, parts needed, and so on. For spot-on guidance, it’s best to check your appliance’s manual or reach out to us if you’ve got questions.

What it means when your mini split freezes

When your mini split starts icing up, it’s usually because something’s throwing off its normal cooling cycle. The evaporator coil needs good airflow to work right. If airflow gets blocked the coil can get super cold, and the moisture on it turns into ice. 

Knowing why your mini split’s freezing up helps you fix it the right way. Often, you can sort out freeze-ups with a simple cleaning or a tweak to your system. But it’s important to nail down the exact cause before you start any repairs.

Common reasons mini splits freeze

Your mini split can freeze up for a bunch of reasons. Usually, it’s something that throws off the balance of temperature and airflow around the evaporator coil. Here are some common troublemakers:

Restricted airflow

When the airflow’s blocked, cold air piles up in one spot on the coil instead of moving through the system like it should. This makes the coil drop below freezing. Common airflow problems include:

• Dirty air filters clogging the intake
• Blocked vents
• Dusty or dirty evaporator coils
• Fan blades covered in debris

Faulty temperature sensor or thermostat

Some mini splits use sensors to keep track of coil temperature and indoor air temperature. If a sensor’s giving bad readings or has come loose, the system might run too cold before it shuts off. Just repositioning the sensor or swapping it out might fix the problem. Many sensors clip onto a specific spot on the coil, so if it’s out of place, the coil can get colder than it should and frost over.

Clogged drain lines

Drain lines carry away condensate from the indoor unit. If they get blocked, water can back up around the coil. Since the coil’s cold, the standing water can freeze. As the coil ices up, more moisture builds up, leading to a thick layer of ice. Clearing the clog can solve the freezing issue and stop any messy leaks.

Running the system in very cold weather

Even though lots of modern mini splits can handle colder temps, some older models or basic units aren’t built for extreme cold. In really chilly conditions, the outdoor unit might have trouble, and the indoor coil can get colder than it should when cooling. If your manual mentions limits on outdoor temperatures, be mindful of that when using the system in certain seasons.

How to fix restricted airflow

Fixing airflow problems is often the easiest way to stop ice from forming. You want air to flow freely over your mini split’s coil. Here’s how to deal with airflow issues step by step:

1. Turn off the power: Flip off the mini split at the breaker or power switch to stay safe.
2. Remove and inspect the filter: Open up the front panel on your indoor unit. Slide out the filter(s). If they’re dirty, give them a gentle rinse with lukewarm water, or replace them if they’re disposable. Make sure they’re completely dry before putting them back.
3. Check the vents: Make sure nothing’s blocking the air intake or output. Furniture, curtains, or debris can all mess with air circulation.
4. Clean the evaporator coil: If you can safely get to the evaporator coil, gently remove dust with a soft brush or a coil cleaner. Be careful not to bend the delicate fins. Take your time—bent fins can mess up airflow and performance.
5. Check the blower and fan blades: Dust can build up on the blower wheel over time. With the power still off, gently clean any visible debris from the wheel and fan blades using a soft cloth.
6. Put it back together and power on: Once everything’s clean and in place, turn the power back on and run a test cycle. Keep an eye out for any leftover ice or airflow issues.

Correcting temperature sensor or thermostat errors

A faulty sensor or thermostat can make the coil colder than it should be, leading to freezing. Here’s how you can tackle sensor issues:

1. Find the temperature sensor: Look for the sensor near or on the evaporator coil—it’s usually a small probe with wires. Your mini split’s manual can help you pinpoint it.
2. Check its position: Make sure the probe is clipped or placed properly against the coil. If it’s come loose or is hanging away, gently put it back where it belongs.
3. Look for damage: See if there are any frayed wires or cracks in the probe. If the sensor looks damaged, replace it with the right part for your model.
4. Test it out: Turn the power back on and see if the coil runs at the right temperatures. If ice shows up again, you can test the sensor with a multimeter by checking resistance values according to your mini split’s specs.
5. If your mini split uses a separate wall thermostat, a bad control board or wiring can also send the wrong signals about coil temperature. In that case, check that the wiring is secure and the thermostat is calibrated right. 
6. If you think the thermostat is the problem, try a factory reset or swap the batteries if it’s wireless.

Unclogging the drain line

If a clogged drain line or drain pan is causing water to build up and freeze, clearing the blockage is key. Frozen or dirty drain lines are often easier to fix than you’d think:

1. Turn off the system: Before you get started, switch off the mini split to be safe.
2. Find the drain line: The drain line usually runs from the indoor unit through an exterior wall. You might see it exiting outside or going to a drain.
3. Look for visible dirt or blockages: Use a flashlight to check if any debris is partially or fully blocking the line.
4. Flush the line: Use a small burst of compressed air or a vacuum on the end of the line to clear obstructions. Carefully flush the line with water or a mild cleaning solution to remove any leftover buildup.
5. Clean the drain pan: If you can safely take out the drain pan, wipe it clean and make sure there’s no mold or algae. Many drain pans have a small hole leading to the drain line—make sure it’s clear.
6. Test the system again: Turn the power back on and run a cooling cycle. See if water flows properly out of the drain line. If ice still forms, you might need to look into other causes like restricted airflow.

Moving forward  

We hope these tips helped you to take good care of your mini split. If you need more help, feel free to visit AppliancePartsPros.com for parts and resources, or check out our repair help section for detailed troubleshooting. We’d love for you to follow us on social media platforms like Facebook and Twitter for more tips and tutorials. If you’ve got questions or need help finding the right parts for your mini split, just reach out to us. We’re here to help, and we want you to feel confident tackling DIY appliance repairs.

If you’re still not sure about any step, check your manufacturer’s documentation or learn how to find your specific model number here to get the most accurate instructions.