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How To Troubleshoot A Mini-Split Air Conditioner Not Coming On Or Cooling

by Feride Halma

A mini-split air conditioner installs on the outside and inside of the house. The outside unit is made up of the compressor, condenser, and fan, while the indoor unit is comprised of the air handler, evaporator, and expansion valve. 

Many things can go wrong with a mini-split unit, but a common problem is the unit not coming on or cooling. You may be tempted to call a repair service, however, you can troubleshoot the issue yourself by following this guide.

Fix Leaks

Mini-split units use a refrigerant to cool the air that is circulated by cables, which could get damaged. Usually, the first sign of a refrigerant leak occurs when the system turns on, but it doesn't blow cool air.

Find the end of the drain line close to the outdoor unit, and check for clogging with a water bottle. Insert the bottle on the drain opening, hold the rim of the bottle with your hand on the drain hose, then squeeze the bottle to remove debris. Use a wet/dry vacuum to remove puddles of water inside. If the hose seems unclogged, check the fan coil for the correct slope.

Inspect Settings and Power

Another cause of the air conditioner not turning on is the temperature and time setting. The TIMER mode sets a schedule for the unit to turn on, so check the TIMER setting, and turn it on or cancel it.

Try raising the pre-set temperature, and make certain you have the unit on the COOL setting. Inspect the fan coil to ensure it is set on FAULT mode, which should display an E with a number, and look up the code in your manual

If the remote fails to turn on the unit, the batteries may need replacing. Replace the batteries every six months, and check the area for corrosion before you install them. 

Make Room

Mini-split systems are more effective when they have plenty of room to operate, so move any objects around the indoor unit that may interfere with the remote.

Large objects, such a bookcases or sofas, collect dust, so avoid placing these near the indoor components. The unit needs at least four feet of space between the indoor components and wall.

Check Vents and Filters

Dirty filters and vents can cause the unit to not cool efficiently. If the filters are dirty, remove them, and wipe them with a damp cloth. It is ideal to replace or clean filters once every several weeks to improve efficiency.

Remove the vent covers, and shine alight down them to check for obstructions. If you find them clogged, contact an HVAC service like Allied Mechanical & Electrical, Inc..