Heating & Cooling

Mini-Split Troubleshooting Guide: 18 Common Problems Solved!

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Mini-split heat pumps are one of the most efficient heating and cooling systems you can use to condition your home. They operate entirely on electricity and use limited energy to produce maximum comfort. Mini-splits can handle heating and cooling, which is very practical, but also means they undergo extra wear and tear. 

Because mini-split systems run year-round, several issues can happen. While there’s a chance you can resolve some of these problems on your own, many of them will require professional assistance. Understanding why issues are happening and what you should do about them is essential. 

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The goal of this article isn’t to focus on any specific mini-split brand but rather to look at problems prevalent throughout the industry. We’ll examine the most common mini-split issues, what they mean, troubleshooting tips, and what you should do to fix them. Let’s get started! 

Your Condensate Line is Clogged or Kinked 

One of the most common problems that mini-splits run is that the condensate drain gets clogged or kinked. The part of the line that attaches directly to the indoor unit of the mini-split consists of plastic. When your installer pushes the unit against the wall to mount it during installation, it’s possible for this portion of the drain to kink. 

It’s also possible for dust, dirt, and debris to accumulate inside the condensation reservoir of the mini-split. When this happens, there’s a good chance it will clump together over time and clog your drain line. In most cases, your mini-split will sense the unusual water buildup and turn itself off.

At other times it will continue operating and accumulating condensation until water spills over the reservoir and drips behind the mini-split, down your wall, and into your home.      

You’ll have to remove the clog or fix the kink to get your system draining again. 

Float Switch Malfunction 

Another possible cause of condensation overflow is your float switch or condensate pump isn’t working. The problem is the same as if the drain line is clogged or kinked when this happens. You will have to fix or replace the float switch or condensate pump for the condensation to drain properly. 

A float switch or condensate problem can result from a faulty item, a frayed or loose wire, or a bad circuit board. You’ll need a multimeter and electrical experience to diagnose and fix the problem. 

Ice Buildup on the Indoor or Outdoor Coil

Ice buildup on the indoor or outdoor coils is a big problem that typically has an underlying cause. You should think of the ice buildup as a symptom rather than the main issue. Most mini-splits have a built-in defrost system that will shut down the mini-split and defrost the icy coils before they start up again. 

Ice buildup can result from dirty air filters, low refrigeration, or a busted fan motor. Either way, you’ll have to fix the source of the problem, or your coils will continue to ice over. 

Mini-Split Is Running but not Blowing air. 

If your mini-split runs, you likely have a busted fan motor, but you don’t feel air coming out of the front vents. Your mini-split works by sucking the air out of the room where the head unit is mounted. Thanks to refrigeration and the evaporator coils, the air gets heated up or cooled inside the unit. 

Once the air is heated or cooled, a fan inside the unit blows it through the front vents of the head unit. This process continues until the set temperature gets reached. If the fan isn’t working, hot or cold air will accumulate inside the head unit but have nowhere to go. A busted fan often causes the evaporator coils to overheat or over cool; the problem will only go away by fixing or replacing the motor. 

The System Won’t Turn On. 

If your ductless mini-split system doesn’t power on, it’s either because of an electrical problem or an error code that has shut down the system. In the case of an error code, you’ll have to resolve the issue to get the system working again. For power issues, however, here’s what you should do. 

  1. Check the remote for weak batteries. Install new batteries in the remote if needed.
  2. Make sure the circuit breaker is on. 
  3. Check the electrical wiring to ensure the wires are secure and in the right place. 
  4. Check the disconnect next to the outside unit and ensure it’s turned on. 

Communication Problems Between the Indoor and Outdoor Units 

A communication wire connects the indoor and outdoor units and allows them to work together. Due to mini-split installation errors, the wires may not be attached to the units in the same order, which will throw off the communication. There’s usually a red, white, blue, black, or green wire inside the communication wire that attaches to various terminals on either unit. 

If these wires don’t get connected in the same order, are over-tightened, or under-tightened, your system won’t operate. It’s also possible that the wire is pinched or severed between the two units. 

The Air Coming Out of Your Mini-Split Smells Bad 

If the air from your ductless mini-split smells bad, there’s a good chance you need to clean the inside of the unit. Remember, the air is constantly sucked into the unit, cleaned, and redistributed. This process means that all the nastiness from the air stays inside the system. Over time, this accumulates enough to make the unit’s air smell funky. 

Dirty Air Filters 

Dirty filters usually accompany foul-smelling air from a mini-split. The air filter is the component that traps the dirt, debris, and particles from air getting sucked into the head unit. After a while, the accrued nastiness will make your air start to stink. 

Another possible problem caused by dirty air filters is that they get so clogged that air can no longer pass through them. A clogged filter means that it can no longer clean air, but it also means that not enough air can get through the filter to satisfy your thermostat. 

Turn the system off to clean your air filters and solve this problem. Lift the front cover of the indoor unit and remove the air filters inside. Soak them in lukewarm or cool water and wipe them off to remove the dirt. 

The Unit Isn’t Cooling Properly

If your mini-split is blowing hot air, but it isn’t cold, the first thing you should do is check the setting. If the setting is on COOL but cold air isn’t happening, you likely have iced up coils or low refrigerant. Without ample refrigerant, mini-split systems can’t perform correctly.

If there isn’t enough refrigerant in the system, there won’t be enough coolant to effectively cool the air getting sucked into the head unit. 

Only heating and cooling technicians with Freon, AC gauges, and experience can check for an insufficient refrigerant level, leaky refrigerant lines, or put refrigerant back into your system. 

The Unit Isn’t Heating Properly

A unit that isn’t heating could be the same problem as when the unit isn’t cooling properly. Iced-over coils or a refrigerant leak are both possible. However, it’s also possible that your mini-split has a heat exchanger that isn’t working properly.

Your best bet is to contact a licensed HVAC technician to diagnose and repair the problem. 

The Mini-Split Isn’t Dehumidifying

Everyone knows that a mini-split is supposed to cool the air inside your home when operating in cooling mode. However, it’s also supposed to draw the humidity out of the air and remove it from your home. The humidity removal is what the condensation drain in the back of the mini-split is for. 

When working correctly, you should see dripping water from the condensate discharge pipe.

If your ductless system is too big for the space it’s operating in, it will satisfy the air temperature and turn off before it can remove humidity. There’s also possible mold in the condensate drain or reservoir, which will cause problems with dehumidifying. 

Electrical Malfunctioning 

Because mini-splits operate completely on electricity and many internal and external electrical components, a lot can go wrong. The electrical wire supplying the condenser may be too small to operate the mini-split unit. It’s also possible that one of the wires is loose or overtightened or that the wire is damaged. 

Most electrical issues will cause your system to shut down and refuse to turn back on. Before your mini-split works again, you’ll have to find out what’s happening with your electrical wiring and where the problem lies. 

The Compressor Breaks Down 

The compressor is in the outdoor condenser of your mini-split system. Its job is to compress the refrigerant within the system and either superheat or supercool it, depending on what mode you’re running it in. Because it operates year-round, the compressor gets put under more stress than a traditional air conditioner

A good sign that your compressor is bad is that your system runs non-stop but doesn’t produce air at the right temperature. Replacing a compressor is expensive unless your mini-split is still under warranty. 

Mini-Split is Too Big or Small 

Sizing problems with ductless mini splits are common. Your mini-split might be working just fine, but it either constantly runs or only runs for a short period. Turning off too soon often happens because your unit is too big or too small for the square footage it’s trying to condition.

A mini-split size that’s too big will shut down before it has time to remove humidity from the air. 

When we refer to the mini-split size, we refer to the BTUs or tonnage. For example, a 24000BTU (2-ton system) heating or cooling a space less than 600 square feet would be too large and cycle off and on rapidly.

However, a unit that’s too small will run non-stop, which eliminates the efficiency that mini-splits are known for. You must have a professional size up and install your mini-split to ensure this doesn’t happen. 

For more on this, read How Many Mini-Splits Do You Need? Single Vs Multi-Zone Systems.

Low Refrigerant Levels 

Low refrigerant levels are almost always the result of a refrigerant leak. Leaks can occur within the evaporator coils on the inside or outside unit or in the refrigeration lines. Regardless of where the leak is, the result is that your evaporator coils will freeze up or overheat or that your head unit will produce lukewarm air. 

Only an HVAC pro can refill your system with freon and locate the leak to repair it. 

Improper Installation 

Mini-splits aren’t overly difficult to install, but there are a lot of small details that are extremely important. Kinking the condensate drain line, overtightening or under-tightening electrical or communication wires, not leveling the outdoor unit, and many other things can cause mini-split malfunctions. 

Mini-splits cannot be installed by an HVAC professional. There are tricks to the trade and fine details that only installers trained in the way of mini-splits will know. You should ensure that the installer of your mini-split is a seasoned veteran who knows exactly what they’re doing. 

Damage to the Outdoor Condensor

Most of the problems we’ve looked at having to do with the indoor unit or a connected component. However, damage to the outdoor condenser can also negatively impact how your mini-split operates. The condenser requires ample space around and above the unit so that it has room to circulate air. 

You should also mount the condenser safely above the ground to protect against snow, ice, or water buildup. Ensure not to plant shrubs or bushes too close to the outdoor unit and to build a roof or covering over the top to protect it from snow and ice buildup. 

The Mini-Split is Making Weird Noises 

Strange noises emanating from your mini-split are extremely common. Some of these noises are problematic, but others are perfectly natural and shouldn’t cause concern. 

  • Popping or clicking noises 

Though they may sound strange, popping and clicking noises are normal. As your mini-split operates, the plastic housing around the indoor unit expands and contracts, making a popping or clicking noise. 

  • Swooshing or gurgling noises 

Swooshing or gurgling noises can mean normal condensation drainage out the back drain. However, it could also mean that your mini-split is switching to defrost mode because your evaporator coil is iced over. 

  • Squealing on the outdoor unit 

A shrill, squealing, or squeaking noise around the condenser indicates bent or damaged fan blades or the compressor is giving out. 

  • A gentle hum or whir

During normal operation, you should hear a gentle hum or whir of the fan motor and the sound of air coming out of the front vent. 

Mini-Split Error Codes

If your ductless mini-split keeps displaying an error code, this error will usually point you to the cause of the problem. Here are some major brand troubleshooting guides:

Related Questions 

Are mini-splits hard to troubleshoot? 

Mini-splits are easier to troubleshoot than heating and cooling devices because of their error codes. They often flash the error code on the front of the unit or the remote control, making it easy to identify a problem. 

How do you troubleshoot a mini-split? 

The best way to troubleshoot a mini-split is to identify the error code on the front of the unit or your remote control. Once you know the code, you can look it up in your owner’s manual or online, telling you the problem. From there, you either fix it yourself or hire a pro. 

How do I check the freon level in my mini-split? 

To check freon levels in a mini-split requires hooking gauges up to the mini-split system and running a series of diagnostic tests. Getting an accurate reading of your freon levels is impossible without the proper equipment and training. Only HVAC professionals or service technicians know how to check freon levels. 

Final Thoughts 

As you can see, many problems can occur with mini-split heat pumps. However, this holds for all heating and cooling appliances and isn’t unique to mini-splits.

Lack of maintenance is often the root cause of most malfunctioning mini-split HVAC systems. Like HVAC systems, ductless mini-splits need regular maintenance. For more, see Maintain & Service Heat Pumps (7 Things You Should Know).

Despite their downfalls, mini-splits remain one of the best and most efficient ways to heat or cool your home. As long as you know what to look for, you can catch minor problems before they become major ones.

Do You Need HVAC Installation, Service or Repair?

Get FREE quotes from licensed HVAC contractors in your area today. Whether you need a new install, service, or basic repair We Can Help! All HVAC contractors are screened, licensed, and insured.

Get a FREE Quote Today
We earn a commission if you purchase at no additional cost to you.

Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.