A ductless, or mini-split, air conditioner may be just what you need for a home addition or other existing space where no ductwork is present. The system has two components – an outdoor unit that resembles that of a traditional air conditioner, and one or more indoor units. The components are connected to each other with electrical wires and refrigerant tubing, requiring only a hole in the wall rather than the expensive installation of new ducts.

Ductless air conditioner maintenance is similar to maintaining a traditional air conditioner, but there are some important differences. Here is what you should know about mini-split maintenance, troubleshooting and repair.

Common ductless air conditioner problems

Ductless air conditioners, like any piece of machinery, can occasionally have problems. Some ductless air conditioner repair jobs can be done by the average homeowner, while others require the services of an HVAC professional. Fortunately, basic ductless air conditioner troubleshooting is relatively easy, allowing you to see if a simple fix is enough or if you will need to call a pro for further diagnostics and mini-split repair. Here are some of the most common problems:

Unit won’t turn on

If your mini-split air conditioner won’t turn on, start by checking the power supply. Most likely, the unit came unplugged or a circuit breaker tripped. If everything looks good with the power, troubleshoot the issue by trying both the remote and the unit itself.

If it turns on at the unit but not with the remote, try changing the remote batteries. If the remote works but you can’t operate the system at the unit, the thermostat may be broken. If neither works, the unit itself is likely broken. Call a professional for assistance. Repair costs vary depending on your geographic area and exactly what the problem is, but generally run a few hundred dollars.

Unpleasant odor

Sometimes mini split troubleshooting is as simple as following your nose. These units work by absorbing warm air from your home and passing it through cooler evaporator coils, which leads to condensation. If the system is not properly maintained, the coils and drain pan can become stagnant and even moldy. If you catch the problem soon enough, though, you may be able to remedy it with a thorough cleaning.

Turn the unit off. Wash or replace the air filter, and then follow the instructions in your owner’s manual to clean the condensate drain line, evaporator coils and drain pan. Dry everything thoroughly and then turn the system back on. If the odor is gone, you should be in the clear. If not, then it’s time to call for professional help. The evaporator may have gone bad from lack of maintenance or there could be a water leak behind the air handler. The price of the repair depends on the specific issue and your geographic location, but could range anywhere from $150 to $750 or so.

Temperature problems

A mini-split that refuses to cool the room can be tricky to diagnose, as the problem could be anything from dirt to a refrigerant leak. Start by turning the system off and changing the air filter, then check the outdoor unit for any dirt or debris such as twigs and leaves. Clean the fan if you can reach it. Turn the unit back on and see if the problem is fixed. If not, then an HVAC professional will need to check the refrigerant in your unit. A refrigerant leak repair is typically under $500, depending on your location.

Noise issues

If your previously quiet ductless air conditioner is suddenly banging, squealing, knocking or whining, it can be extremely frustrating. These noises always signal some kind of problem within the system itself, but there are a number of possible causes. Bent fan blades, twigs or other debris in the unit, and many other factors can cause your mini-split to suddenly make a lot of noise.

It’s worth turning off the unit and seeing if there is anything obvious that you can easily reach. Otherwise, it’s best to call an HVAC professional to figure out and repair the problem. Costs vary depending on what is found, but ductless air conditioner repairs rarely cost more than $1,000.

General maintenance tips for ductless air conditioners

Although it would be impossible to prevent every repair issue, good maintenance can go a long way toward reducing your risk of problems and extending the useful life of your ductless air conditioner. Always check your owner’s manual for specific recommendations, but here are a few general maintenance tips for mini splits:

  • Leave space around indoor units: Your ductless air conditioner needs a good, unrestricted supply of room air. Never place furniture, curtains or other household items close to a unit.
  • Dust indoor units: Use a duster or a damp rag to remove dust from the outside of all indoor units on a regular basis.
  • Wash or change filters: Many ductless air conditioners have washable filters, while others have disposable filters that need to be replaced. Either way, clean or replace the filter every two months or as recommended in your owner’s manual. You may need to do this more often if you have pets or if anyone in your home suffers from asthma or allergies.
  • Clean the outdoor unit: Every few weeks, or when you notice visible dirt and debris, turn off the outdoor unit and spray down the evaporator coils with a garden hose. Don’t use high pressure, as this could bend the fins. If you notice any bent fins, use a special fin comb (readily available at big box stores and online) to gently push them back into alignment.
  • Run the system: If your ductless air conditioner is in a vacation home or a part of your house that is infrequently used, the system may not be run on a regular basis. To extend its lifespan and guard against repair problems, turn it on at least once each season and let it run for a few minutes.
  • Schedule twice-annual professional service: Have your ductless air conditioner professionally inspected and serviced twice each year – once before heating season and once before cooling season. Your HVAC professional will check the system carefully, looking for signs of emerging issues that could become major problems over time.

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