Why is my mini split AC blowing warm air? Causes and fixes

Ever turned on your mini split AC only to feel a gust of warm air hitting you in the face? Talk about annoying! We get it, you just want to chill out, literally. This article’s here to help you figure out why your mini split isn’t giving you that cool breeze you desperately need, and what you can do to fix it.

The info in this article might not match your exact appliance model. While we aim to throw out handy tips for all sorts of DIY appliance fixes, different models and setups can mean different troubleshooting steps, error codes, parts, you name it. For the best advice, make sure to check your specific appliance’s manual or give us a shout if you’ve got questions.

Why your mini split AC blows warm air

There’s no one-size-fits-all answer to why your mini split AC is spewing warm air. A bunch of things could be causing it. Basically, something’s getting in the way of cool refrigerant moving through the system. Maybe it’s an airflow hiccup, or perhaps a refrigerant leak is to blame. Below, we’ve rounded up some common reasons and how you can tackle them yourself.

Thermostat or control settings

Sometimes the issue is right under your nose: the thermostat settings. If your thermostat, or the mini split’s remote control, is set up wrong, your AC might not cool the way you expect. It might even be stuck on heat mode or “fan only,” meaning no cool air is being generated.

Checking and adjusting settings

1. First off, make sure the system is set to “Cool” or “Auto” mode. Heat or fan-only modes won’t give you cold air.
2. Double-check that the temperature setting is lower than the current room temperature. If it’s set higher, the AC won’t kick in to cool the place down.
3. See if there’s a timer or schedule active that’s messing with your cooling commands.
4. If you think the remote or thermostat is acting up, try swapping out the batteries or hitting the reset button if there is one. Some units have fancy controls that might require a peek at the user manual.

Dirty or clogged air filters

Your air filters are the gatekeepers of your mini split AC’s indoor unit, keeping dust and debris from clogging up the coils and blocking airflow. When these filters get too dirty, they can seriously mess with your cooling performance. Restricted airflow means the AC can’t cool the incoming air properly, leaving you with warm air blowing out.

How to address dirty air filters

1. Before anything else, power down your mini split to stay safe.
2. Open up the indoor unit’s front panel and find the air filters. They’re usually removable plastic frames covered with a mesh or fabric filter.
3. Carefully remove the filters. If they’re disposable, toss them and pop in new ones. If they’re washable, rinse them under lukewarm water to get rid of dust, then let them air dry.
4. Put the clean filters back where they belong and close up the panel.
5. Turn the system back on and see if you’re finally getting that cool air.
6. Making it a habit to check your air filters every month is a smart move, especially during peak usage times.  

Blocked or dirty coils

Your mini split AC has evaporator coils inside and condenser coils outside. If these coils get dirty or blocked, heat exchange goes out the window, and you might end up with warm air blowing into your home.

Cleaning the coils

1. Make sure the system is turned off. Remove the access panels on both the indoor and outdoor units.
2. Look for dirt, dust, or debris on the coils. Use a soft brush or a coil cleaning spray made for HVAC systems. Steer clear of harsh chemicals that could damage the coil fins.
3. Gently rinse away any loosened gunk with low-pressure water. Be extra careful to keep water away from electrical components.
4. Check that the coil fins aren’t bent or damaged. If they’re bent, you can straighten them out with a fin comb.
5. Let everything dry completely before putting the units back together and turning them on.

Clogged condensate line

Your mini split system pulls moisture out of the air, creating condensate (water) that usually drains through a condensate line. If this line gets clogged, water can back up and cause all sorts of issues, like reduced cooling performance. You might even notice puddles forming or the unit shutting down to protect itself. Even if the system keeps running, a partially clogged line can mess with how well your AC cools.

How to clear a clogged condensate line

It’s a good idea to check the condensate line now and then, especially during humid months, to prevent buildup. That way, you can avoid warm air issues and potential water damage.

1. Find the condensate drain line and make sure the mini split is turned off.
2. Look for blockages at the end of the drain line (usually outside your home). Remove any visible debris by hand or with a small brush.
3. Use a wet/dry vacuum to gently suck out any clogs from the line. Alternatively, you can pour a mix of warm water and mild detergent into the drain line if it’s easy to access.
4. Check the drain line for leaks or cracks. Replace any busted sections. To get the right tubing size and part number, check out how to find your appliance’s model number.
5. Reattach everything securely, turn the power back on, and see if the AC starts cooling properly again.

Frozen indoor unit

A frozen indoor unit can actually lead to warm air. When moisture around the coils freezes up, it can block airflow and cause the system to blow less air, or even warm air, because it can’t cool properly.

Thawing a frozen indoor unit

1. Turn off your mini split system. Running it while it’s frozen can cause damage.
2. Open up any accessible panels around the indoor coils. Look for layers of ice or frost.
3. Wait for the ice to melt naturally. You can speed things up by pointing a fan at the coils, but don’t try to chip away the ice.
4. Figure out what’s causing the freeze: is the filter dirty, or is there low refrigerant? Check out the earlier sections on filters or refrigerant leaks to get to the root of the problem.
5. Once all the ice is gone, close up the panels, turn the system back on, and see if it’s cooling properly.

Refrigerant leaks

Low refrigerant levels often come from leaks in the system’s sealed components. Refrigerant is key for absorbing heat from inside your home, and without enough of it, your AC can’t cool effectively. That often leaves you with nothing but warm air blowing out.

Signs of a refrigerant leak include hissing noises coming from the unit, frost or ice on the coils, and weaker cooling performance. If your energy bills suddenly spike, that could also be a red flag.

How to address refrigerant leaks

1. Turn off the power to your mini split AC for safety. Double-check that any breaker switches connected to the unit are off.
2. Inspect the accessible lines and coils for visible signs of damage. If you spot oil-like residue or corrosion, those could be leak spots.
3. If you find a leaky area, look for loose connections or damaged parts. Consult your unit’s manual or use our how to find your appliance’s model number guide to order the right replacement parts.
4. Carefully replace any damaged components. When dealing with refrigerant parts, follow all safety guidelines. The system can be pressurized, and you don’t want any accidental releases.
5. If needed, recharge the system with the correct type and amount of refrigerant. Only do this if you have the proper tools and it’s allowed for your unit.
6. Turn the unit back on and monitor how it’s working. Make sure there are no new leaks.

Compressor issues

The compressor is basically the heart of your mini split AC, pushing refrigerant through the system. If the compressor fails or isn’t working efficiently, you might end up with warm air. Sometimes the issue comes from an electrical problem, like a faulty capacitor or bad wiring that’s keeping the compressor from running right.

How to address compressor troubles

1. Shut off power to the mini split at the breaker.
2. Open the panel that houses the compressor and look for signs of burnt wiring, disconnected terminals, or melted insulation.
3. Use a multimeter to check the resistance in the compressor’s windings. Compare your readings to what’s recommended in the service manual. If things are off, the compressor might be on its last legs.
4. Test the start and run capacitors. If a capacitor is bulging or leaking, it’s probably shot. Replace it with one that matches the part number.
5. If the compressor is confirmed dead, swap it out with the exact model meant for your mini split system.
6. Turn the power back on and see if you’re finally getting cool air again.

Additional information

Thanks for reading! If you need replacement parts, grab your model number and head to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need help finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

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