Why Is My Mini Split Not Cooling?

The last you checked, your ductless mini split system was supposed to both heat or cool your home. The heat function is working fine, but the cooling? It’s just not happening.

You hear your mini split turn on, and you feel some air coming out, but the air feels lukewarm at best. What’s going on?

This is many times do to a refrigerant leak but could also be due to a 4-way valve, a wire problem, and many other issues.   

Refrigerant, which is also known as freon, is a common fluid in air conditioning systems, including your mini split cooling system.

Here’s how refrigerant should work. The refrigerant travels throughout your mini split system and absorbs the heat from your home. During this time, the refrigerant transforms into a low-pressure gas.

The gas becomes compressed, which increases its pressure as well as its temperature. The refrigerant, still in its gas form, travels throughout the mini split’s coils.

As the refrigerant’s temperature comes down, it converts back into a liquid. In this state, the liquid refrigerant will enter the mini split’s expansion valve. Rapid cooling will lower the refrigerant’s temperature and cause evaporation.

Now, when your mini split system begins to leak refrigerant, the above cooling method cannot transpire. Hence, your mini split isn’t blowing cold air like you'd expect.

So what causes refrigerant leaks? There are all sorts of causes, so let’s take a closer look now.


  • The flares are set at the incorrect torque. You might be able to fix this with a head torque wrench, but if you’re not comfortable, it’s best to call your mini split technician.
  • The copper tubing might have become compressed or squashed over time. Your technician can use tools like a unibit or a reamer to shape the copper tubing. They can also replace the tubing if it’s too bent out of shape.
  • The flare adapter or flare face is scratched, which now allows refrigerant to travel out of these openings.
  • The wrong type of flare nut is installed, which could crack under the pressure of the refrigerant and allow it to leak.
  • The flare connection is too tight, leading to damaged or cracked flares.

If you suspect that something is wrong with one or more of the components of your ductless mini split system, the best option is to call your technician and tell them what’s been going on with your mini split.

The technician can repair the leak and restore your mini split to operational order. Before you know it, the next time you turn your mini split on to a cool setting, you’ll feel nice, cold air coming out of the air-handling unit.

This is not one of those problems that will go away on its own. The lost refrigerant makes your mini split system less efficient overall, so don’t wait if you sense an issue!