Mitsubishi Mr Slim Troubleshooting Manual Simplified!

A Mitsubishi Mr. Slim, like every other air conditioning split system, sometimes won’t work. Once that’s the case, having the most user-friendly Mitsubishi Mr Slim troubleshooting manual is priceless as you will likely fix it DIY. 

A troubleshooting manual can help you fix your Mitsubishi Mr. Slim when it turns on, blows cold or hot air, or when its remote control, heat mode, or compressor is not working. Moreover, you can interpret and fix blinking lights. 

Perhaps you’ve checked your original manual, and it seems cumbersome! Well, that’s the reason behind this troubleshooting guide. 

I’ll take you through the issues mentioned above, common among Mr. Slim users, to show you how to troubleshoot them. My approach is simple to enable you to do the troubleshooting DIY and not have to pay someone.

So, tag along as we explore the issues that could be failing your air conditioner and depriving you of clean air and a comfortable temperature at home. 

Mitsubishi Mr Slim Troubleshooting Manual

In a rush? Find below the quick troubleshooting guides for the aforementioned AC issues.

Simple Mitsubishi Mr Slim Troubleshooting Manual

Problem  Possible Causes Fixes
1.Mr. Slim Not Turning OnPower disruption due to a blown-up fuse, flipped breaker, defective outlet, or faulty cable. Or a non-responsive remote or bad compressorReset a flipped breaker and replace the fuse, power cord, or power outlet if any lacks continuity. Meanwhile, ensure the remote is working and replace the compressor if it’s not working
2.Mitsubishi Mr Slim Not Blowing Cold Air  Filthy filter, coil or outdoor unit, wrong AC size, low refrigerant, or bad thermistor, fan motor or control moduleClean the air filter or condenser if dirty, clear the outdoor filth, and ensure you have the right unit size. Leave the repairs to an expert.
3.Mitsubishi Mr Slim Not Blowing Hot Air  Wrong mode or temperature settings, smaller AC, or dirty filterSet the unit on heat mode or choose a higher temperature setting than the room. If the air filter is filthy/congested, clean or replace it
4.Remote Control Not Working Long range, wrong battery polarity, exhausted batteries, pressing the wrong button, or damaged remote sensor/LEDMove the remote close to Mr. Slim, replace drained batteries, and fit them correctly. Meanwhile, ensure you press the right button but if the sensor is damaged, replace the remote control
5.Mitsubishi Mr Slim Heat Not WorkingPower failure, low coolant, unmaintained outdoor, or defective heat pumpReset a flipped breaker, replace a faulty fuse or heat pump, and clear outdoor filth. However, call an expert if you suspect a low coolant level
6.Compressor Not Working Filthy filter or condenser coil, blown-up fuse, low coolant, or electrical faultClean the air filter and condenser coils if they are dirty, and replace a blown-up fuse. Call an expert to fix a low coolant level or electrical fault
7.Mr Slim Blinking LightClogged filter or coil, low refrigerant, or electrical faultClean the air filter or coil if dirty and call an expert to fix a low coolant level or electrical fault

How to Troubleshoot a Mitsubishi Mr Slim Not Working?

Here is a simple Mitsubishi Mr. Slim troubleshooting manual guide to using on the seven most typical air conditioner problems:

1. Mitsubishi Mr Slim Not Turning On

Several issues could prevent Mr. Slim from turning on, ranging from power disruption to a non-responsive remote or failing compressor. Here’s how to go about them:

a) Power Disruption

Unless Mr. Slim gets electric power, it won’t start. So, consider checking for possible power disruption while focusing on these issues:

  • Blown fuse – Once the thermal fuse blows up due to a current or power overload, it cuts off the AC’s power supply. So, Mr. Slim won’t turn it on. 
  • Flipped breaker – A flipped breaker has the same effect as a blown-up fuse. It cuts off the power supply and prevents Mr. Slim from starting.
  • Defective or overloaded power outlet – If the power outlet is faulty, Mr. Slim won’t have enough power to turn it on. Likewise, if you plug in numerous appliances alongside Mr. Slim, the AC won’t turn on.
  • Faulty power cable – If the power cable is broken or defective, the AC split system won’t receive enough power to turn on.


Check the breaker and reset it if it is flipped. Test the thermal fuse, power cable, and power outlet for continuity using a multimeter and replace the part that lacks continuity. As for the last part (power outlet), don’t overload it.

b) Mitsubishi Mr Slim Not Responding to Remote

If your Mr. Slim remote control is not working (for any of the reasons shared in number 4 below), the AC split system won’t turn on when you press it.


Check the recommended fixes in number 4 below

c) Bad Compressor

Sometimes the air conditioner system won’t start because the compressor won’t turn on. So, consider the issues discussed under number 6 to see what could prevent the compressor from working, or it could be that the compressor is dead. 


Consider checking for a compressor fault or replacing the compressor if it’s dead.

Mitsubishi Mr Slim Not Turning On

2. Mitsubishi Mr Slim Not Cooling (Won’t Blow Cold Air)

Your Mitsubishi air conditioner split system may fail to blow cold air for different reasons, resulting in a heated space. These reasons are as follows:

a) Filthy Filter, Condenser, or Outdoor Unit

If the air filter, condenser coil, or outdoor unit is dirty, your Mr. Slim may fail to cool entirely. Dirt interferes with the unit’s steady airflow and compromises its cool ability.

For that reason, you should inspect the indoor and outdoor units for filthiness.


Inspect the indoor unit’s filter and condenser for dirt clogging and clean them. And if there’s too much filth around the outdoor unit, clear it. That includes debris and unmaintained twigs.

b) Wrong AC Size

It won’t cool if the air conditioning system is bigger or smaller than the space. And if it does, you may not feel the cold air blowing. 


Ensure you get the right AC split system that matches the space you want it to cool.

c) Low Refrigerant

The refrigerant/coolant directly impacts Mr. Slim’s cooling activity. If the level drops, mainly due to leakage, the remaining refrigerant won’t be able to absorb the extra heat, and so the unit won’t cool your space accordingly.


A leaky refrigerant isn’t easy to fix. Hence, call an HVAC expert to determine the cause of the leakage and fix it. 

d) Bad Thermistor Fan Motor or Control Module

Lastly, if the reason for Mr. Slim not blowing cold air is none of the above, it could be because of a failing thermistor, fan motor, or control module. If these parts are bad, the AC system won’t cool.


Consider contacting an expert HVAC technician to help you identify a bad thermistor fan motor or control module and fix it. 

3. Mitsubishi Mr Slim Not Heating (Won’t Blow Hot Air)

Since Mr. Slim is an air conditioning split system, you expect it to heat as much as it cools. It, however, may sometimes fail to blow hot air, and it could be due to any of these issues:

a) Wrong Mode 

Ensure your Mr. Slim is running on the correct temperature mode. For example, putting it in cool mode won’t allow it to heat but will initiate a cooling cycle. 


Set the unit on heat/auto mode if you want it to heat and not cool. 

b) Wrong Temperature Setting 

You must also ensure the selected temperature setting is not lower than the room temperature. If it is, Mr. Slim won’t blow cold air.


Adjust the unit’s temperature to ensure it is slightly higher than the room temperature. Alternatively, turn the unit to Heat Mode.

c) Smaller AC

If the air conditioning split system is smaller than the manufacturer recommends for your space, it won’t heat up. 


Ensure your Mr. Slim is the right size and matches the space you want to heat up.

d) Dirty Air Filter 

Dirt restricts airflow across the air filter, and as a result, it can prevent the AC split system from blowing hot air. 


Inspect Mr. Slim’s air filter for dirt-caking and clean or replace it. 

Mitsubishi Mr Slim Not Cooling

4. Mitsubishi Mr Slim Remote Not Working

Now, consider these issues if your Mr. Slim remote control is not working:

  • Long range – If you hold the remote control a long distance from Mr. Slim, the AC won’t work. 
  • Wrong battery polarity – If you mistakenly place the batteries incorrectly in the remote, the remote won’t work.
  • Exhausted batteries – If the batteries are dead, they won’t power the remote control. So, the remote control won’t work. 
  • Pressing the wrong buttons – If you are pushing the wrong buttons on the remote control, the remote control will not work or may malfunction.
  • Damaged remote sensor/LED – The remote depends on the LED sensor at the front to respond to commands. If this sensor is damaged, the remote control won’t work. 


Operate the remote control as close to Mr. Slim as possible. If it still doesn’t work, check the batteries’ polarity to ensure they are correctly installed.

If the remote won’t work, replace the batteries but if the problem is the LED/sensor, replace the remote. 

5. Mitsubishi Mr Slim Troubleshooting No Heat

If the AC split system heat mode is not working, it might be due to one of these issues:

  • Power failure – An issue like a bad fuse or flipped breaker can prevent the heat mode from taking effect. So, check them.
  • Low coolant – A refrigerant leakage may also prevent the AC’s heat mode from working.
  • Unmaintained outdoors – If the outdoors is unkempt (too much filth around the outdoor unit), the heat mode will fail to come alive. 
  • Defective heat pump – Lately, if your heat pump is faulty, the AC unit won’t heat up.


Look for a flipped breaker and reset it. If the thermal fuse doesn’t show continuity, replace it, and so should you replace a defective heat pump. However, if the issue is low coolant, call an expert. 

6. Mitsubishi Mr Slim Compressor Not Working

The compressor is an essential part of Mr. Slim’s operations. Its failure may mean no cooling, heating, or even turning. Overall, these are issues that could prevent the compressor from turning on:

  • Filthy filter or condenser – Dirt-caking on the air filter and condenser causes the compressor to struggle to turn up and may fail to do so.
  • Blown fuse – A blown-up fuse cuts off the compressor’s power supply. So, the compressor won’t turn on. 
  • Low coolant – A low refrigerant can also prevent the compressor from turning on just as much as it can prevent the AC from heating or cooling. 
  • Electrical fault – If an electrical fault touches the compressor, the compressor may not turn on. 


Clean the air filter or condenser coil if any is dirt-caked, and replace the fuse if blown (it won’t show continuity). Call an expert if the issue is low coolant or an electrical fault. 

Mitsubishi Mr Slim Not Heating

7. Mitsubishi Mr Slim Troubleshooting Blinking Light

Lastly, consider these culprits if your Mr. Slim AC system won’t stop blinking its indicator light:

  • Clogged filter or coil – Mr. Slim may warn you of a dirt-congested filter or condenser coil by blinking repetitively. So, inspect the two for filthiness.
  • Low refrigerant – Once the refrigerant level drops, the AC may blink green to indicate a significant leakage. 
  • Electrical fault – Sometimes, Mr. Slim blinks the light when there’s a wiring issue. Only an expert can troubleshoot that, however. 


Inspect the air filter and coil from clogging and clean them if that’s the case. Call an expert, however, if the problem is a low coolant level or an electrical issue. 

Closing Thought

Now you have a Mitsubishi Mr Slim troubleshooting manual you can use when your unit is not working or starts to malfunction.

Consider it if you find your original Mr. Slim manual too bulky, especially when you are in a hurry or cannot access one. It, however, does not replace the original manual.

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