The scorching summer heat is here, and there’s nothing worse than realizing your Mitsubishi mini split air conditioner isn’t blowing cold air. Instead of enjoying cool comfort, you’re left sweltering in a hot home.

Before you call in the pros, try troubleshooting the issue yourself. In most cases, a DIYer can get their Mitsubishi unit cooling again with minimal effort. This comprehensive guide will walk you through the top 10 reasons a mini split fails to blow cold air and how to fix each problem.

Common Causes of a Non-Cooling Mini Split

Several issues can disrupt the cooling capabilities of your Mitsubishi mini split system. Here are the most common culprits when the AC stops blowing cold air:

• Clogged Air Filter: Restricted airflow from a dirty filter prevents proper cooling.
• Wrong Mode: If the unit is switched to “Heat” instead of “Cool”, it will blow warm air.
• Frozen/Dirty Coils: Blocked airflow due to icy or dirty evaporator and condenser coils.
• Power Disruption: A tripped breaker or blown fuse interrupts power to the AC.
• Unmaintained Unit: Dust and debris in the outdoor unit components reduce performance.
• Refrigerant Leak: Low refrigerant levels due to a leak prevent the AC from cooling properly.
• Clogged Drain Line: Condensation can’t drain leading to operational issues.
• Faulty Compressor: Worn out or damaged compressor fails to circulate refrigerant.
• Defective Thermistor: Disrupts the cooling signal to the AC.
• Broken Fan Motor: Motor failure leads to lack of airflow.

By methodically troubleshooting each issue, you can get your Mitsubishi mini split blowing crisp, cold air again in no time.

Steps to Troubleshoot a Non-Cooling Mini Split

When your mini split stops blowing cold air, don’t panic. Just follow this systematic troubleshooting guide to identify and fix the issue:

1. Check the Air Filter

The first thing to check is the indoor air filter. A clogged, dirty air filter is the most common reason an AC fails to properly cool.

Over time, dust, pet hair, and other debris builds up on the filter screen. This clogs the filter and restricts airflow over the indoor unit’s evaporator coil. Less air circulation means less efficient cooling.

How to Fix:

• Turn off and unplug the mini split.
• Remove the front panel from the indoor unit to access the air filter.
• Slide out the filter and inspect it. If it’s excessively dirty, clogged, or coated in debris, it needs to be cleaned.
• You can vacuum the filter to remove loose dirt and dust. For heavier grime, wash the filter in warm soapy water. Rinse it thoroughly.
• Allow the filter to air dry completely before reinstalling it. Never put a wet filter back into the unit.
• Replace the clean filter, replace the front panel, and turn the mini split back on.

Be sure to check and clean the air filter every 3-6 months. Filters should be replaced at least once a year. Proper maintenance keeps airflow unrestricted for better cooling.

2. Verify the Temperature Mode

Another simple issue is having the wrong temperature mode activated on your mini split remote control or panel.

For cooling, the unit needs to be set to “Cool” mode. If it’s mistakenly switched to “Heat” mode, the system will blow warm air instead of cold.

How to Fix:

• Check your remote control or indoor unit panel to verify which mode is currently selected.
• Switch the mode to either “Cool” or “Auto”.
• “Auto” mode will automatically adjust between heating and cooling as needed to maintain the set temperature.
• The “Dry” mode on some units also activates cooling.

This allows the mini split to start lowering the room temperature and blow cold air as needed. Make sure it’s not stuck on heating mode when trying to beat the summer swelter.

3. Inspect the Coils for Frost or Dirt Buildup

The evaporator and condenser coils are vital components that can get blocked in various ways, preventing proper airflow and cooling distribution.

First, check for frost or ice buildup on the evaporator coil inside the indoor unit. In very hot and humid conditions, the evaporator coil can freeze over which blocks air from passing over it. Without airflow, the refrigerant won’t absorb heat and cool the air.

Next, inspect the condenser coil in the outdoor unit. Over time, dirt, dust, leaves, and other debris can stick to the coil fins blocking airflow. A filthy condenser coil prevents hot air from circulating and heat from dissipating properly.

How to Fix:

For frozen evaporator coils:

• Set the mini split to run the fan at high speed. This will help thaw out the ice buildup.
• You can also try carefully removing any ice with your hands if it’s accessible.
• Once thawed, be sure to keep the filter clean and airflow unobstructed to prevent it from freezing again.

For dirty condenser coils:

• Turn off the power to the outdoor unit.
• Remove debris like leaves and dirt from the coil fins using a soft brush.
• Rinse gently with a garden hose if needed.
• Be careful not to damage the thin, aluminum coil fins which can affect performance.
• Straighten any bent fins using a fin comb tool.
• Clear away grass, weeds, or shrubbery right near the condenser. Allow at least 12 inches of clearance.

Keeping both the evaporator and condenser coils clean allows proper airflow for the mini split to cool efficiently.

4. Check for Power Disruptions

When troubleshooting why your mini split won’t blow cold air, you also need to look for any power supply issues. Loss of electrical power will shut down the entire AC system.

Check your main electrical panel for any tripped circuit breakers or blown fuses related to the mini split circuit. A tripped breaker or blown fuse cuts power to the unit. Power disruptions like a grid outage will also cut power.

How to Fix:

• Locate the circuit breaker for the mini split and ensure it’s switched to the “On” position.
• If it’s tripped to “Off”, flip the switch to reset the breaker.
• Check fuses using a multimeter to see it they are still functional. Replace any blown fuse with a new one of the same amperage.
• For suspected electrical issues, it’s best to contact a licensed electrician.

Restoring steady electrical power to your mini split will allow it to turn on and resume cooling your space.

5. Clean the Outdoor Unit

For optimal operation and cooling capacity, the outdoor unit of your mini split needs periodic maintenance. The outdoor unit contains vital components like the compressor, condenser coil, and a fan motor.

Over time, dust, dirt, leaves, grass clippings, and other debris can accumulate inside the outdoor unit housing. Excessive buildup on these components blocks proper airflow which reduces cooling performance.

How to Fix:

• Turn off power to the outdoor unit at the breaker and disconnect any electrical connections.
• Remove the top cover panel so you can access inside the unit.
• Use a soft brush and vacuum cleaner to gently remove dust and debris from the condenser, fan blades, and other components.
• Take care not to bend, damage, or disturb any refrigerant lines or electrical parts.
• Use a damp cloth to wipe dirt from the compressor body. Avoid getting any components dripping wet.
• Replace the cover when finished and restore power.

Routine cleaning keeps the condenser, fan, and compressor operating at peak efficiency for better cooling.

6. Address Refrigerant Leaks

The refrigerant circulating through the mini split system is vital for heat absorption and cooling. If there is a leak, the reduced refrigerant level can greatly affect performance.

Signs of a refrigerant leak include:

• Damp spots around fittings, valves or coils in the outdoor unit. The evaporating refrigerant leaves oil residue.
• Unusual odors around the unit like a sweet, chemical smell.
• Higher utility bills from added run times due to reduced cooling capacity.
• The system may still run but never quite reaches the set temperature.

How to Fix:

If you suspect a refrigerant leak, immediately contact an experienced, licensed HVAC technician. Refrigerant systems are complicated and specialized tools/skills are required to properly diagnose, repair, evacuate, recharge, and test for leaks.

Trying DIY repairs often makes the problem worse and releases refrigerant which is harmful to the environment. The EPA requires proper refrigerant handling certification.

The technician will use leak detection dye and an electronic sensor to pinpoint the source of the leak. Then they can seal it, recharge the system with new R410A refrigerant, and get your mini split blowing cold air again.

7. Unclog the Drain Line

Room air conditioning units like mini splits remove humidity from the air during cooling. This condensation needs to drain away properly.

The indoor unit has a drain tube or pan that empties excess moisture outside. Over time, algae, slime, dirt, and debris can clog the drain line. When clogged, condensation builds up inside the unit rather than draining away. This water overflow can disrupt normal operation.

Signs of a clogged drain line include:

• Water dripping from the indoor unit into your home.
• Excess moisture visible inside the unit.
• Reduced cooling and musty odors from excess humidity buildup.

How to Fix:

The best solution is to have an HVAC technician inspect, clean, and unclog the drain line completely. They can also treat the line to prevent future algae growth and clogging issues.

For DIY cleaning:

• Shut off and unplug the mini split.
• Locate the drain line port on the indoor unit (usually a rubber grommet).
• Disconnect the drain line and examine it for obstructions like sludge, algae, dirt.
• Clean out debris with a wet/dry vacuum suction tool.
• Flush with hot water, vinegar, or drain cleaner.
• Rinse thoroughly since chemicals can corrode the coil if any residue remains.
• Reconnect the cleared drain line.

Keeping the drain line clear prevents excess humidity and allows proper water drainage for optimal cooling.

8. Check the Compressor

The compressor in the outdoor unit is the heart of the mini split system. This component circulates refrigerant through the indoor and outdoor coils to provide cooling. If the compressor is worn out or defective, the system loses its ability to cool properly.

Signs of compressor failure include:

• Unit runs but doesn’t blow cold air.
• Unusual noises from the outdoor unit like screeching, grinding.
• Outdoor unit cycles on and off frequently.
• Frost or ice buildup on the refrigerant lines.
• High utility bills from increased runtime.

How to Fix:

If you suspect compressor failure, call an HVAC technician immediately. Diagnosing issues accurately requires specialized tools and expertise.

The technician will check for:

• Bad start capacitors – Needed to start the compressor motor.
• Burned out motor windings.
• Damaged valves or bearings.
• Leaks, cracks or broken fittings.

Repairing a compressor may be possible, but a technician is the best option to evaluate the extent of the damage. In many cases, total compressor replacement is needed.

Trying to recharge refrigerant in a unit with a bad compressor will likely worsen any leaks. Paying an expert to properly inspect and fix or replace a faulty compressor will get your system running optimally again.

9. Inspect the Thermistor

The thermistor (also called a thermal sensor) is a component that measures temperature changes in the refrigerant flowing through the system. It sends signals to the circuit board to adjust cooling output accordingly.

If the thermistor in the outdoor unit fails, it disrupts this vital communication between temperature measurements and cooling needs. The system won’t know to increase cooling when it gets hotter.

Signs of a faulty thermistor:

• Erratic cooling – Unit frequently switches between warm and cold.
• Icing up of the evaporator coil due to lack of temperature monitoring.
• Temperature swings – Thermostat setpoint and actual room temp don’t match.

How to Fix:

Thermistors are delicate and complex. Diagnosing and replacing a bad outdoor unit thermistor should be done by a trained HVAC technician.

They will use a multimeter to check thermistor resistance and determine if it is still within the correct ohm range. If faulty, the thermistor will need to be replaced with a new OEM part.

Proper thermistor operation is crucial for monitoring system temperatures and maintaining ideal cooling.

10. Replace Broken Fan Motor

The outdoor unit contains a fan motor that blows air over the hot condenser coil to dissipate heat. If this condenser fan motor burns out, airflow will be reduced through the outdoor unit hampering its ability to cool.

Signs of a broken motor:

• Loud grinding, buzzing noises.
• Fan spins slowly or not at all.
• Outdoor unit has to work harder causing the compressor to overheat and shut down.

How to Fix:

Replacing a burned-out condenser fan motor requires an exact OEM part number match and specialized skills to remove, rewire, and reinstall.

Contact a Mitsubishi authorized HVAC technician. Only a Mitsubishi OEM replacement motor will have the correct specs for your unit. Attempting to install a generic motor may hinder performance and cooling capacity.

When to Call an HVAC Technician

While many mini split problems can be DIY repaired, more complex issues require a professional. Contact a qualified HVAC technician for:

• Refrigerant leaks – Recharging and finding leaks requires EPA 608 certification. Improper handling releases harmful refrigerants.
• Drain line clogs – Severe obstructions in drain pipes may need professional rodding, jetting, or chemical treatments.
• Compressor failure – Only a technician has the tools to accurately diagnose compressor issues. Compressor repair or replacement is specialized work.
• Thermistor problems – Faulty thermistors need an expert diagnosis. Replacing them means handling refrigerant lines.
• Condenser fan motor – Exact OEM replacement parts and proper installation is crucial.
• Any major disassembly of sealed refrigerant components. Tampering voids warranties and releases refrigerants.

While some home DIY repairs are possible, mini splits are complex appliances. At the first sign of any refrigerant or sealed system-related problems, engage a certified HVAC company to get your unit running right.

Maintain Your Mini Split

Preventative maintenance is key to avoiding many mini split problems in the first place. Follow this schedule:

Monthly:

• Check and clean air filters if needed. Replace every 3-6 months.
• Clear away debris and vegetation around outdoor unit.

Every 3 months:

• Clean dirt from outdoor unit coils with gentle water rinse.
• Check for obstructions in air intake and outlet vents.

Yearly:

• Replace air filters before summer and winter seasons.
• Have an HVAC technician do a seasonal maintenance check-up and inspect refrigerant charge.

As Needed:

• Clean fins on outdoor coils if they get bent or dirty.
• Have drain lines professionally cleaned if you notice water leakage.

Enjoy Reliable Cooling from Your Mini Split

Mitsubishi makes incredibly efficient and reliable mini split air conditioners. But like any appliance, they can occasionally have hiccups.

If your unit starts blowing warm air instead of crisp, cold air, don’t panic. In most cases, the problem is minor and easily fixed with some DIY troubleshooting.

This guide walked through the top 10 most common issues that cause a mini split to stop cooling properly. By identifying the specific problem and methodically trying repairs, you can get your unit running optimally again.

Knowing when to DIY and when to call in an HVAC professional prevents further damage or safety risks. With proper maintenance and care, a quality Mitsubishi mini split system should provide many years of energy-efficient cooling comfort.

Beat the summer swelter by keeping your Mitsubishi mini split operating at peak performance. Refer back to these troubleshooting tips anytime your AC needs a quick pick-me-up!

Conclusion

A non-cooling Mitsubishi mini split can be frustrating, especially during hot weather. But in most cases, the issues can be quickly identified and repaired with some basic troubleshooting.

• Start by checking for simple problems like a dirty filter, incorrect mode, or power supply interruption.
• Inspect components like the coils, outdoor unit, drain line, and fan motor for common maintenance issues.
• For more complex problems involving refrigerant, the compressor, thermistor or major repairs, engage a trained HVAC technician for safe diagnosis and servicing.

Preventative maintenance goes a long way in keeping your mini split running optimally year-round. But even well-maintained units can sometimes malfunction.

Now you’re equipped with the troubleshooting knowledge to get your Mitsubishi mini split blowing crisp, cold air in no time. Keep this guide handy for when your system needs a tune-up.

With just a few DIY repairs, you can stay cool and comfortable thanks to a properly operating mini split AC even on the hottest days!