Mitsubishi Mr Slim Troubleshooting

The Mitsubishi Mr. Slim is a popular ductless mini-split air conditioning system known for its efficiency and reliability. However, like all HVAC systems, it may encounter issues from time to time. This troubleshooting guide will help you identify common problems and provide solutions to keep your Mr. Slim running smoothly.

1. No Cooling or Heating



  • Adjust thermostat settings as needed.
  • Reset circuit breaker or replace blown fuses.
  • Replace remote control batteries.
  • Clean or replace air filters regularly to maintain proper airflow.

2. Insufficient Cooling or Heating

Possible Causes:

  • Dirty Evaporator or Condenser Coils: Accumulated dirt can reduce heat exchange efficiency.
  • Refrigerant Leak: Low refrigerant levels can result in poor cooling or heating.
  • Blocked Air Vents: Ensure that there are no obstructions in front of the indoor or outdoor unit.
  • Incorrect Sizing: If the system is undersized for the room, it may struggle to maintain the desired temperature.


  • Schedule professional maintenance to clean coils and check for refrigerant leaks.
  • Clear any obstructions from the unit and its vents.
  • Consult a HVAC specialist if the system is undersized for the space.

3. Strange Noises

Possible Causes:

  • Loose Parts: Vibration can cause screws or other components to come loose.
  • Fan Issues: Damaged or dirty fan blades can create noise.
  • Refrigerant Issues: Gurgling or hissing sounds may indicate refrigerant problems.


  • Inspect the unit for loose parts and tighten as necessary.
  • Clean or replace damaged fan blades.
  • If refrigerant issues are suspected, contact a professional.

4. Water Leaks

Possible Causes:

  • Clogged Drain Line: A blocked drain line can cause water to accumulate.
  • Improper Installation: If not installed correctly, condensation may not drain properly.


  • Clear any blockages in the drain line.
  • Check the installation for any issues and contact a professional if necessary.

5. Remote Control Problems

Possible Causes:

  • Battery Issues: Weak or dead batteries in the remote control.
  • Signal Interference: Other electronic devices or obstructions may interfere with the signal.


  • Replace remote control batteries.
  • Ensure there are no obstructions between the remote and the unit.

6. System Not Responding

Possible Causes:

  • Electrical Issues: A power surge or electrical problem may have affected the system’s control board.
  • Sensor Malfunction: Faulty sensors can disrupt system operation.


  • Reset the system by turning off the power for a few minutes and then turning it back on.
  • If the problem persists, contact a professional technician for a thorough inspection.

Remember that some troubleshooting steps may require professional assistance, especially when dealing with refrigerant issues, electrical problems, or complex sensor malfunctions. Regular maintenance and professional servicing can also prevent many common problems with Mitsubishi Mr. Slim systems, ensuring their longevity and optimal performance.


7. Ice Buildup on Indoor Unit

Possible Causes:

  • Low Refrigerant Levels: Inadequate refrigerant can cause the evaporator coils to freeze.
  • Dirty Filters or Coils: Reduced airflow due to dirty components can lead to ice buildup.
  • Thermostat Settings: Extremely low temperature settings can also cause freezing.


  • Ensure the thermostat is set to a reasonable temperature.
  • Replace or clean air filters regularly.
  • Schedule professional maintenance to check for refrigerant leaks and clean coils.

8. Inconsistent Temperature

Possible Causes:

  • Incorrect Thermostat Placement: If the thermostat is in direct sunlight or near a heat source, it may not accurately measure room temperature.
  • Improper Sizing: An oversized unit may cool or heat the room too quickly, leading to uneven temperatures.
  • Air Leaks: Gaps around doors and windows can allow conditioned air to escape.


  • Relocate the thermostat if necessary to a more representative location.
  • Consult with an HVAC specialist to ensure the system is appropriately sized for the space.
  • Seal any air leaks around doors and windows to improve insulation.

9. Foul Odors

Possible Causes:

  • Dirty Air Filters or Coils: Accumulated dirt and debris can create musty smells.
  • Mold or Mildew Growth: Moisture buildup in the system can lead to mold growth.


  • Regularly clean or replace air filters.
  • Schedule professional maintenance to clean the coils and inspect for mold or mildew growth.

10. System Won’t Turn Off

Possible Causes:

  • Thermostat Issues: A malfunctioning thermostat can prevent the system from shutting off.
  • Wiring Problems: Faulty wiring or connections can cause continuous operation.


  • Check the thermostat for any faults and replace if necessary.
  • If the issue persists, consult a professional technician to inspect the system’s wiring and control board.

11. Error Codes on Display

Mitsubishi Mr. Slim systems often have error codes that provide valuable information about the problem. Consult the user manual for your specific model to decipher these codes and take appropriate action. Error codes can help pinpoint issues with sensors, refrigerant levels, or other system components.

12. Routine Maintenance

Prevention is key to avoiding many common issues with Mitsubishi Mr. Slim systems. Consider these maintenance tasks:

  • Regular Cleaning: Clean or replace air filters every 1-3 months and ensure that the evaporator and condenser coils are clean and free from debris.
  • Professional Servicing: Schedule annual or bi-annual professional servicing to inspect and maintain the system, including checking refrigerant levels, cleaning coils, and verifying electrical connections.
  • Keep the Area Clear: Ensure that there are no obstructions around the indoor and outdoor units to allow for proper airflow.

Mr. Slim Not Cooling

IssuePossible CauseSolutionTools RequiredAdditional Notes
No cool airRefrigerant leakCheck for leaks and repairPressure gaugeConsult professional if needed
Insufficient coolingDirty air filtersReplace or clean filtersScrewdriverRegular maintenance is crucial
Compressor not runningFaulty thermostatTest and replace if necessaryMultimeterEnsure wiring is correctly done
Inadequate refrigerant chargeRefrigerant lossRecharge refrigerantCharging kitProfessional help may be required
Evaporator coil icingRestricted airflowClear obstructions and improve airflowVacuum cleanerMonitor for proper airflow

Mr. Slim Noisy Operation

IssuePossible CauseSolutionTools RequiredAdditional Notes
Loud rattling or bangingLoose componentsTighten screws and boltsScrewdriverRegularly inspect for loose parts
Clicking or ticking soundsExpansion/contractionNormal operation, no action neededCommon in temperature changes
High-pitched squealingBlower fan issuesLubricate or replace the blower fanLubricant, toolsBe cautious with moving parts
Hissing or gurgling noisesRefrigerant leakLocate and repair leaksLeak detectorProfessional help may be required
Humming or buzzingElectrical problemsCheck electrical connectionsMultimeterShut off power before inspecting wiring

Mr. Slim Remote Control Issues

IssuePossible CauseSolutionTools RequiredAdditional Notes
Remote not respondingDead batteriesReplace batteriesNew batteriesCheck for correct battery placement
Signal interferenceObstructions or distanceReposition the remoteEnsure direct line of sight to the unit
Remote malfunctionDirty or damaged buttonsClean or replace the remote buttonsCleaning kitHandle with care when opening remote
Infrared sensor issuesBlocked sensor on the unitClean the sensor on the indoor unitCleaning kitAvoid touching sensor directly
Programming errorsIncorrect settings or codesReset and reprogram the remoteUser manualFollow instructions carefully

Mr. Slim Water Leaks

IssuePossible CauseSolutionTools RequiredAdditional Notes
Water dripping indoorsClogged drainClear the condensate drain lineDrain brushRegular maintenance is essential
Water puddling indoorsEvaporator coil icingImprove airflow and defrost coilVacuum cleanerMonitor for proper unit operation
Water around outdoor unitRefrigerant leakLocate and repair refrigerant leaksLeak detectorProfessional help may be required
Condensation on ductsPoor insulationInsulate ducts to prevent condensationInsulation tapeProperly insulate all exposed ductwork
Unit sweating outdoorsHigh humidityInstall a condensate drip tray or lineTray, tubingEnsure proper drainage away from the unit

 Mr. Slim Electrical Issues

IssuePossible CauseSolutionTools RequiredAdditional Notes
Unit won’t turn onPower supply issuesCheck circuit breaker and power sourceCircuit testerEnsure proper power supply to the unit
Frequent trippingOverloaded circuitReduce electrical load or add circuitsElectricianAvoid using high-powered appliances together
Blown fusesElectrical faultReplace blown fusesFuse pullerInvestigate and fix the underlying issue
Burning smellOverheating componentsShut off power and inspect for damageVisual inspectionDo not attempt to restart if overheating
Voltage fluctuationsUnstable power supplyInstall a voltage stabilizerStabilizer unitProtect the system from voltage variations


Remember that troubleshooting and maintenance can vary slightly depending on the specific model of your Mitsubishi Mr. Slim system, so always refer to your user manual or contact the manufacturer’s customer support for model-specific guidance.

Regular attention to these troubleshooting steps and maintenance tasks will help ensure your Mitsubishi Mr. Slim system operates efficiently, provides consistent comfort, and has a longer lifespan.

Mitsubishi Mr Slim Troubleshooting

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