How to Repair a Ductless Mini-Split Heat Pump - Troubleshooting Tips

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Ductless heat pumps, or mini-splits, are becoming trendy among homeowners when it comes to efficient and cost-effective heating and cooling homes. Though they work like traditional heat pumps, they require less space and are more flexible for handling.

However, like most heat pumps, mini-splits are also prone to many similar problems. This article will discuss common issues your mini-splits might have and how to troubleshoot them.

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Common ductless heat pump problems

Firstly, let’s briefly discuss how ductless heat pumps work. Like most heat pumps, mini-splits have an outdoor unit with a compressor and an indoor unit with an air handler, connected with the refrigerant lines and electrical wires. However, as the name implies, they don’t have or need ductwork. And unlike typical heat pumps, a mini-split’s indoor unit is directly installed in the room that needs to be heated or cooled.

Now that we have an idea of how a mini-split works, let’s discuss the common problems we can encounter with these HVAC units. Some of these problems are similar across traditional heat pumps, so some of these might be easier to troubleshoot than others.

5 common problems of the ductless heat pumps are:

  1. Heat pumps get iced over
  2. Issues with the refrigerant and reversing valves
  3. Broken outdoor fan
  4. Condensate line problems
  5. Power supply problems

Note: The most common cause of a mini-split ductless heat pump failure is improper installation.

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Heat pump gets iced over

Mini-splits also encounter freezing, especially during winter, which is one of its most common problems. A little snow and frost gathering on your outdoor unit during winter is usual. However, excessive ice buildup might damage inner parts. If your mini-split is working correctly, it should enter defrost mode after a specific period. Though optional, you could use a drain pan heater to combat this. However, if the ice is not cleared soon enough, it could damage the coils, fins, and the compressor.

If your heat pump is still working correctly, addressing these outdoor factors should be enough. This includes clearing snow and leaves from and around the unit and ensuring that no gutter water is dripping on it. You also need to ensure that the unit’s grounding is stable. Placing the unit on the stable ground will ensure proper draining and protection from other debris.

However, if there is still ice buildup even after fixing these, this might point to a more serious problem. Some of the things to check for may include the valve, refrigerant, outdoor fan, and other components. It’s possible that one of these might be broken or malfunctioning. In this case, this might require some professional help. And if you need one, you can submit a form here and get the call with free estimates.

Issues with the refrigerant and reversing valves

Ductless heat pumps are refrigerant-dependent like many other HVAC units, so they are susceptible to refrigerant leaks as well. The refrigerant level is one of many internal causes for frozen coils and, by extension, the unit itself. If the refrigerant levels are low, it will be hard to heat the system in defrost mode. If you suspect that there’s a leak in your refrigerant, get it checked soon before it grows. Some signs that could point to refrigerant leaks are loud noises and less hot or cold air in your home. When this happens, you need to call your local technician to help.

But note that low refrigerant is not the only thing to watch out for. Some units have preset refrigerant levels, but sometimes you need to add more. Be careful as too much refrigerant might stop your unit from turning on.

You might also want to check the reversing valves because they are designed to keep refrigerant flowing through the coils. The coils will freeze if the valve cannot help transfer the refrigerant to heat the coils. Your unit will still work, but it might only work in one mode in that situation.

Broken outdoor fan

A broken outdoor fan is another thing to look out for. For starters, your unit won’t cool properly because the fan can’t dispel the cold air stuck in the unit. The cold air will drastically drop the temperature in the unit and will likely cause the coils to freeze over. In turn, the refrigerant will not flow and eventually cause the system to break down eventually if left unattended.

Condensate line problems

For ductless mini-split heat pumps, as the name implies, there are no ducts for you to maintain. Instead, you need to check the condensate line of your mini-split. The condensate line goes together with the wires connecting your indoor and outdoor units along with your refrigerant and power lines. The job of condensate lines is to remove moisture from your indoor unit, so it doesn’t leak into your home.

To see if your condensate line is leaking, check the walls where your indoor unit is mounted. Leaks from the condensate line could weaken the area between the wall and the back of the air handler. Observing your unit is one way to prevent this. Regularly check the condensate lines for clogs caused by mold and bacteria buildup as clogs are one of the causes for condensate line leaks. If left unchecked, this buildup might also cause bad odor to spread in your house. Call for maintenance to clean the condensate line so you won’t need to call repairs for your wall.

Power supply problems

Problems regarding power supply are common too, but are relatively easy to fix and troubleshoot. The usual problems include tripped circuit breakers and disconnection of the unit from the main power supply. To troubleshoot, check the heat pump if it’s switched on. If both the circuit breakers and the unit are fine but the heat pump won’t still turn on, check the remote controller. To see if it’s working, try turning on the unit manually or turn it on using the thermostat. You can also try the reverse if your thermostat is the problem.

If the unit is fine, but the controller is not working, it might need battery replacement. The same goes for the thermostat; fix or replace the thermostat if it’s a problem. However, if all else fails, it’s most likely that the system itself is malfunctioning. This might include a defective compressor or capacitor, but those problems more or less need professional help.

Most of the mini-split units require 208/230 volts, so make sure to connect it to the proper voltage. Otherwise, if too much or too low of the load is delivered, the electronic board can get damaged.

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When the “problem” is not a problem? Following symptoms do not indicate the heat pump malfunction

The heat pump doesn’t operate immediately

This is happening to prevent fuse blowouts, in a situation when the unit has stopped and immediately turned on again, or when the electric breaker is turned off then on. After a few minutes of stalling, the unit should continue working as usual. You just have to wait.

If the heat pump doesn’t blow the heated air upon turning the unit on, wait for a few minutes (10 min for some models) as the system might be in the defrost cycle.

The heat pump produces a noise

 The flowing sound is coming from the refrigerant running through the pipes, and you can hear it almost immediately after the heat pump turns on.

Due to thermal expansion and contraction, the parts of the heat pump (particularly those made of plastic) could produce squeaky or ticking sound. 

The mechanical, switching or clicking sound happens when the unit operates, such as when the fan or a compressor is running.


The smell coming out of the device is another regular occurrence as the odor from the furniture or other objects gets sucked in and then blows out with the air. Also, the filter might be dirty.

Why do I see the mist?

The mist is released from the indoor unit because the cool air from the unit rapidly cools moisture in the indoor air.

If there is white smoke coming out of the outdoor unit, that means that the defrosting operation generates the vapor.

The unit starts to operate by itself

Some models are designed to start the operation automatically, even if an indoor unit didn’t receive the signal from the remote controller (the power must be on). Such models are equipped with the auto-restart function.

Poor performance

Heat pumps, after long hours of operation, could experience declining performance. The reasons for such a “problem” could be a dirty air filter, intake grill and outdoor port blocked, opened doors and windows, the presence of the heat generated devices, when the fan operates at the very low speed, freezing weather, undersized unit and other. Check out this article to learn how to get your ductless heat pump perform better.

The flap does not swing

The flap, which directs the airflow, does not start swinging immediately. Don’t worry; it will start moving soon after the heat pump first adjusts the position of the flap.

Puddle of water

It is normal to see some water under the outdoor unit. This is condensate dripping from the cool surfaces of the unit.

When to contact the technician

According to the manufacturers, stop using the heat pump and contact an HVAC technician in the following cases:

  1. If the refrigerant leaks.
  2.  If the water from an indoor unit leaks.
  3.  When the breaker trips frequently.
  4.  When there are abnormalities in operation, such as the sound, smoke, or fire.
  5.  When you see some of the error codes on display.
  6.  The power cord is very hot or damaged.
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Maintenance tips for ductless heat pumps

Maintaining ductless heat pumps is almost similar to maintaining conventional heat pumps. Here are some suggestions for ductless heat pump maintenance.

Keeping the outdoor unit clean

Ensuring the cleanliness of your unit and its surroundings can go a long way. These include cleaning the inner components and the immediate ground around the outdoor unit. Here’s what you can do:

  • Clean the air filters regularly, preferably every six weeks. Wiping them down would be enough. Replace the air filters only if they’re damaged or can’t be cleaned anymore.
  • Clear the outdoor unit of any nearby plants or debris. It will need a lot of space to run correctly.
  • Keep the other inner components clean. This refers to the coils and the fins. Clean them with a garden hose, but make sure that you re-align the fins if they get bent while cleaning.
  • Always check the pipes for leaks and clogs. You can do this when you take out the air filter.


The ductless heat pumps are designed to operate without significant problems for a number of years, but like any electrical device, they might fail anytime. And there are many reasons. Some issues can be prevented and solve on your own while others require professional help.

The above tips for maintaining and troubleshooting your ductless heat pump are just some, and they are not complicated. Regular maintenance goes a long way, but it’s also important to know how to fix certain problems. But if you’re in doubt, call your local support to help you out.