Ductless Air Conditioning Not Cooling – What Could Be Wrong?

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Ductless (aka "mini-split") air conditioner systems can offer many benefits to homeowners. However, similar to central and window air conditioning systems, ductless systems can also come with their share of operational issues, such as the unit not cooling. For this post, we've researched the reasons why your ductless system may not be cooling properly and how to remedy these issues.

A ductless air conditioning unit might not be cooling due to the following reasons:

  • Remote or Power Issues
  • Coolant Leaks
  • Central Thermostat Malfunctions
  • Dirty Air Filters
  • The Blower Is Broken

If your ductless unit is not cooling your home properly, and you suspect that you have one of these issues, it's always best to consult with an HVAC specialist for their recommendations. Now, we'll dive into these reasons a bit more to help you understand their underlying causes and how they can be fixed.

Happy Male Technician Repairing Air Conditioner With Screwdriver, Ductless Air Conditioning Not Cooling - What Could Be Wrong?

Remote or Power Issues

an aircondtioning unit with remote controller shown

If you can't get your ductless system to power on, it could mean you may need to replace the batteries in the remote or that you have a power issue with the main unit. If you find that it still doesn't work after replacing the batteries, try resetting your ductless systems control settings. You can find out how to do this by taking a look at your user's manual.

If the reset doesn't work, take a look and your circuit breaker to ensure that the breaker for your A/C system hasn't been tripped (which is a sign that it may be overloaded). Lastly, if none of these attempts get your unit back running again, it may be an issue for a technician to fix.

Coolant Leaks

Coolant or refrigerant serves as the lifeblood of an air conditioner system. When a mini-split system leaks coolant, it will start to blow out cool or warm air instead of cold air. And if your ductless A/C unit is leaking coolant, it's important to fix the leak as soon as possible as it can lead to expensive repairs and even replacement of the entire system. Here are a few signs of a coolant leak:

  • The evaporator coil is frozen.
  • The air conditioner is not cooling properly.
  • There are hissing noises coming from the indoor unit.
  • Small bubbles are coming from areas in the refrigerant line.

If you notice any of the above issues with your mini-split unit, you may have a refrigerant leak issue, and it's best to call an HVAC technician as soon as possible to repair the leak and replenish the coolant levels.

How Do You Know When Your Air Conditioner Needs Freon?

If your ductless air conditioner unit begins to malfunction, a low freon level may be the cause. Below are five signs that it may be time to have an HVAC professional replenish coolant levels.

1. Your home isn't getting cool as quickly

A change in the amount of time it takes to cool your home or space can be an obvious sign that your mini-split system may need a Freon charge. Air conditioner coolant is a gas that flows through the coils of the unit. During this process, the gas absorbs heat and allows the unit to emit cold air to lower the room temperature. If the unit doesn't have enough coolant, it can't cool as efficiently.

2. Ice is starting to form on the evaporator coils

When taking a glance at your unit's evaporator coil, check to see if there is ice building on it. If it is, odds are that you need a coolant charge. When a ductless air conditioner unit doesn't have an efficient amount of coolant, the evaporator coil will become colder than it should be.

The temperature will cause moisture to build on the line, and eventually, it'll freeze up. If you notice that the copper evaporator coils on your ductless have frozen, it's best to contact an HVAC technician for professional diagnosis and potential Freon replenishment.

3. Utility bills are climbing in summer

Has your recent electrical bill skyrocketed? If so, low coolant levels in your A/C unit may be the issue. If your unit doesn't have an efficient amount of coolant during its operation, it's working double-time (and much longer) to keep your home cool. The extra energy expended to do so can result in a noticeable spike in your electric bill.

4. The unit makes strange noises

While ductless air conditioning units are known to make a certain amount of noise during operation, unusual noises can mean something's wrong. If you hear a bubbling or hissing sound coming from your unit, it could be a sign that its refrigerant is leaking and needs to be replaced. In which case, you'll need to call a technician for repair.

5. Its blowing warm air

A mini-split unit that is low on coolant will struggle to produce cool air. You'll notice that the air coming out of the unit is either warm or just barely cool. A good way to confirm this is to grab a thermometer and hold it to the vent to check the air temperature coming from it.

Check out this thermometer on Amazon.

Central Thermostat Malfunctions

Most ductless systems are controlled by a central thermostat, which is used to operate all of the home's air conditioner units. If the central thermostat is broken, it can cause the different blower units to malfunction or render them inoperable. Check the temperature settings on your thermostat to see if it matches the blower settings for each unit. If it doesn't, you may need to have it replaced or recalibrated.

Dirty Air Filters

A dirty air filter may seem harmless, but it can cause major issues with your ductless A/C unit's ability to cool your home. This is one of the leading causes of air conditioner system failure. If your unit's filter is clogged up with layers of dirt and grime, the air conditioner will struggle to pull in air, and it will have to go into overdrive to lower the temperature in a room.

This, in turn, can lead to a shorter lifespan for your mini-split system as well as an increased energy bill due to its lowered efficiency. It's important to clean your filters every couple of weeks to ensure no air blockages.

How Do I Know What Size A/C Filter I Need?

Ductless systems come with custom-made air filters, and unlike window and central air units, they don't require periodic replacing. However, it is recommended that you inspect and clean the air filter every two weeks. Most ductless A/C systems have filters that need only be rinsed with clean water. A dirty filter can cause debris to collect in the condensate produced by the unit, which can cause mold growth and airflow blockages.

Quick steps to clean your ductless air filter:

  1. Power off the unit.
  2. Lift the front panel of the air conditioner and remove it if needed.
  3. Wipe the area around the air filter with a lint-free dry cloth.
  4. Remove the air filter from the unit.
  5. Take the filter and remove any visible dust and dirt.
  6. Next, wash it with mild soap (or detergent) and rinse it thoroughly. Set it aside and allow it to dry in a shaded area. Make sure that the filter is completely dry before placing it back in the ductless unit. When placing the filter back in the unit, ensure that it snaps and is secure (you should hear a click).

Be sure to look at you a user's manual before cleaning the filter for the first time.

The Blower Is Broken

The blower in a ductless A/C system blows air through the unit into the space that it's cooling, and plays an essential role in the unit's operation. Any time that the motor for the blower fails to operate, the unit will not emit cold air or any air at all. A broken blower will also increase the possibility that your unit's evaporator coil will freeze.

When the cooled air inside your A/C unit cannot be expelled, it will cause the evaporator coil's temperature to drop so low that it will begin to freeze over. If you find that your blower's motor is not running, turn the unit off and call an HVAC technician.

How Cool Can A/C Keep My House?

Ductless air conditioner units are designed to cool your house to around 15 to 20 degrees lower than outside temperatures. So, for example, if outside temperatures soar to 120 degrees, don't expect your unit to be able to cool your home down to 68 degrees. There's a reason for this. To cool your home (or apartment) to a temperature lower than 20 degrees from the outside temperature, the unit would have to emit absolutely frigid air, which would cause a great level of discomfort and require way more coolant (and power).

Do Ductless Air Conditioners Need Annual Maintenance?

Happy Male Technician Repairing Air Conditioner With Screwdriver, Ductless Air Conditioning Not Cooling - What Could Be Wrong?

Yes, ductless air conditioners do need annual maintenance. While ductless systems don’t typically need as much maintenance as central A/C systems, some tasks are needed to keep them in good working condition. You can do tasks yourself, and it's also recommended that you have an HVAC specialist come out bi-annually or annually (at least) to inspect your system and perform the necessary maintenance.

Here are a few things that you can do to keep your ductless system maintained throughout the year:

Check and Clean The Air Filters

Ensuring that your air filters are clean and free of debris should be one of your top maintenance items for your air conditioner unit. Doing a monthly check, especially during high pollen and dust seasons, can ensure that your filters can do their job.

Check/Clean Evaporator Coils

Make sure that the coils on the outside unit are free of dust and any accumulated debris. Wipe down the unit with a damp cloth and sweep away any collected dust or debris surrounding it, as this can cause blockages and pest issues.

Inspect The Refrigerant Lines and Fans

Look for any leaks, cracks, or holes in the connectors. Also, listen for any strange or hissing sounds coming from the unit (indicating refrigerant leakage).

Wrapping Things Up

Ductless air conditioner units will require maintenance to continue functioning properly and safely. If you've found that your mini-split unit is no longer cooling properly, it's always best to have the unit checked out by a professional so that they may provide a proper diagnosis and repair or replace your unit.

Have more questions about ductless air conditioner units and HVAC overall? Check out these posts:

Air Conditioner Outside Unit Freezing Up - What Could Be Wrong?

Should Air Conditioners Be Covered In Winter?

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