Mini Split Air Conditioners Troubleshooting Tips

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Ductless mini split ACDuctless mini split AC

Learn how to avoid common problems with mini split air conditioners and heat pumps, how to recognize the symptoms and troubleshoot correctly. The troubleshooting guide is the DIY guide published to help homeowners maintain, repair the unit and save money.

Many factors can affect the normal operation of the AC or heat pump; from the expected wear and tear and age of the system to unexpected compressor failure, improper use or lack of maintenance.

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How a mini split air conditioner (AC) works?

A mini split air conditioner, also known as ductless, is a device designed for heating and cooling the room air in the residential and commercial applications. Ductless, due to the dehumidifying capabilities also guarantee a better quality of the indoor air. Mini-splits have two main parts; an indoor and outdoor unit that incorporates components such the compressor, evaporator and condensing coils, valves, fans, refrigerant pipes, electrical board, and a remote controller to control the operation.

What makes the ductless mini-splits devices popular choice is that they do not occupy too much of the space (they hang on the wall), are easy to install and do not use the duct system. They can be easily installed in new and old homes without rebuilding or retrofitting.

Also, either you are looking to heat or cool one room or several, mini splits could be a good solution for many homeowners, even businesses. Homes can have multiple units installed, and with the zoning capabilities, users can specify the room temperature independently of each other.

Mini split air conditioners can last over 10 years, but can also break, mainly if not properly maintained or if you live in the region with the unpredictable weather.

Troubleshooting air conditioners could be easy for the handyman but could be hard for those who are dealing with such problems for the first time.

This is why we have included the most common problems, symptoms and a mini guide on how properly to troubleshoot an air conditioner. For more complex work, the recommendation is to contact a licensed technician.

How to prevent problems?

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No matter the device you have; air conditioner, heat pump, water heater or a furnace, most of the common problems could be prevented, as long as the device is installed correctly, cleaned and maintained.

Proper installation

Installation of the mini splits is usually easy, especially with the installation kits. It requires you to connect the refrigerant lines and some electrical work between an indoor and outdoor unit. To reduce the number of malfunctioning elements and improper operation, make sure to install the unit per manufacturer instructions.

Clean the filters

  • Filters inside the air conditioners are used to clean the air. If the filters are dirty, a device won’t perform well and will put more stress on the system, which will shorten its life.
  • It is recommended to clean the filters per manufacturer’s instructions. You can use a garden hose or vacuum for this job.
  • If the filter is damaged or there is a sign of mold, replace it.
  • Replace the filter at least once a year, or earlier if it is needed.

Clean the compressor

A compressor is installed in the outdoor unit and is used to enhance the process by increasing the temperature of the refrigerant.

To avoid the problems on the compressor such as overheating, use the garden hose to wash it.

Clean the coils

Clean both indoor and outdoor coils using brushes and cleaning solution.


Maintain the recommended temperatures and avoid freezing or low performance. A drain pan heater can help the unit to operate in colder weather.

Make sure the outdoor unit is protected from the elements. A wind baffle could protect the unit from an adverse wind effect. Make sure the outdoor unit is not covered with the snow or ice.

Check the drain line

Make sure the drain line does not have any obstructions, and the condensate can be removed easily.

Refrigerant line

Check the refrigerant line for a potential leak.

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Check the wiring

If the wiring was not done as required, this could lead to poor or no signal reception. The symptoms of bad wiring or grounding include unreliable heating/cooling; some modes do work some don’t, miscommunication between the remote, outdoor and indoor unit.

Also, inspect the electrical terminals and tightened connections if necessary.

Ensure proper air flow

Make sure there are no air blockages from the furniture or plants.

Common problems

  • An air conditioner or a heat pump is not working.
  • Check out if there is a power failure.
  • You might have a tripped breaker or a blown out fuse. The problem might be with overvoltage or shorted live/neutral wire.
  • Is the timer on?
  • Did you check the temperature settings?
  • If your mini split air conditioner or heat pump is not working, also look for the error code that will show on display, and use that code to identify the problem.

Poor performance in both heating and cooling modes

An insufficient refrigerant level is the leading cause of reduced AC efficiency and performance. While the mini split air conditioners come precharged with the refrigerant, sometimes it is needed to add. Some of the symptoms of the low coolant are the noise, the unit cannot reach or maintain the requested temperature, a unit is working in one mode but doesn’t in the other, and coils are icing over in the indoor unit.

Too much of the refrigerant could result in the unit not turning on, noisy operation and unstable temperature.

Make sure the air filter and intake grill are clean.

A fan is blowing air but is not cooling

  • Check for the ice buildup on the coils and remove it.
  • See if the fan on the indoor unit is working. If not, check the motor or electric board.
  • Check the refrigerant level.
  • Check the fan on the outdoor unit.
  • Check the compressor if it is hot to the touch, or is it making a loud noise.
  • Replace the bad elements.


During the operation, a mini-split unit could produce the squeaking sound due to expansion and contraction, sizzling sound due to defrosting and simple sound of the flowing refrigerant.


While the AC is working absorbed smell from cigarettes, even surrounding objects can be released into the room.

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Water leak

If you notice that the water is leaking from the indoor unit, always check the condensate line to see is it blocked and does it have a proper drain? Ensure adequate drainage to avoid problems.

During the heating operation, an outdoor unit can produce water during the automatic defrosting operation.

A remote controller doesn’t work

If there is a problem with the remote controller, such as when it doesn’t respond… check are the batteries ok or verify that nothing is blocking the receiver. If you have to - contact a supplier and get a new remote. It is a good idea to check the batteries regularly, as they might corrode or leak, and replace them at least once a year.

Note: If there is a problem with the air conditioner such as burning smell, stop the operation and disconnect the power supply or turn off the electrical breaker.

After repairing an air conditioner, run a complete cycle, either heating or cooling to make sure that you have troubleshot the unit properly and everything is working as it should.

Troubleshooting a mini split air conditioner requires a decent electrical knowledge and basic HVAC. Keep in mind that any work should be done with the power off. If you are not sure how to fix the unit, you can always get a professional technician to do it for you.

Video: Mitsubishi mini split AC repair