The Mitsubishi Mr. Slim is one of the most popular split air conditioning systems on the market today. Known for its slim, compact design and energy-efficient performance, these units provide reliable cooling and heating for homes and businesses. However, like any air conditioner, the Mr. Slim can develop issues that prevent it from working properly.
When your Mr. Slim is not blowing cold air, failing to turn on, or having other problems, it can be incredibly frustrating. But there’s no need to immediately call for expensive technician repairs. Many common Mr. Slim issues can be quickly diagnosed and fixed with some simple troubleshooting steps.
This in-depth troubleshooting guide will provide the key information you need to get your Mr. Slim back to providing cool, comfortable air. We’ll cover the most common issues that affect these units and show you how to fix them yourself without having to pay for a service call.
Whether your Mr. Slim is not turning on at all, blowing hot air, making strange noises, or having remote control problems, this guide has you covered. Let’s start by looking at why your air conditioner is not powering up when you press the on button.
Troubleshooting Mr. Slim Not Turning On
When your Mr. Slim air conditioner will not turn on at all, there are several potential causes to check:
Power Disruption
The first thing to check is if power is being supplied to the unit. Some common power disruption issues include:
- Blown fuse – Check your home’s fuse box for a blown fuse that cuts power to the Mr. Slim. Replace any blown fuses.
- Tripped breaker – Check your breaker panel and reset any tripped breakers that disrupt power to the AC unit.
- Faulty electrical outlet – Use a multimeter to test the voltage of the outlet powering the indoor unit. If low or no voltage, the outlet may need replacing.
- Damaged power cord – Inspect the power cord for any cuts or damage that could prevent power flow. Replace cords that are damaged or faulty.
Non-Responsive Remote Control
If the Mr. Slim’s remote control is not turning on the unit, the issue may be with the remote itself. See the remote troubleshooting section later in this guide for potential fixes.
Failed Compressor
The compressor is responsible for pumping refrigerant through the AC system to produce cooling. If the compressor is broken and not turning on, the unit will not start up. This requires a professional repair.
Troubleshooting Mr. Slim Not Cooling
If your Mr. Slim turns on but fails to properly cool your room, there are several possible causes to check:
Dirty Filters, Coils, or Outdoor Unit
- Clogged air filter – Check the indoor unit’s air filter and clean or replace it if dirty. Debris buildup prevents proper airflow.
- Dirty indoor coils – Use a coil cleaner or mild detergent to clean debris and dirt off the indoor unit’s coils.
- Outdoor unit obstruction – Clear away any leaves, dirt or debris surrounding the outdoor condenser unit. Obstructions reduce airflow.
Read more:
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Improperly Sized Unit
- If the Mr. Slim is too large or small for the space, it will not be able to maintain the proper temperature. Confirm your unit is the appropriate BTU capacity for the room size.
Refrigerant Issues
- Low refrigerant levels due to a leak can greatly reduce the AC’s cooling capacity. Have an HVAC technician inspect for leaks and recharge the refrigerant if needed.
Faulty Components
- A malfunctioning part like the thermistor, fan motor or control board can prevent proper cooling. Have a technician diagnose and replace any damaged components.
Troubleshooting Mr. Slim Not Heating
Mr. Slim units that provide both heating and cooling may fail to generate warm air. Potential causes include:
Incorrect Mode Setting
- If the mode is set to “Cool” or “Fan Only”, the unit will not engage heating mode. Switch the mode to “Heat” or “Auto” to activate heating.
Thermostat Set Too Low
- The unit will not blow warm air if the thermostat is set lower than the current room temperature. Adjust the temperature setting higher to engage heating mode.
Undersized Unit
- A Mr. Slim that is too small for the space will struggle to heat the room properly. Confirm your unit has the appropriate capacity for heating your room size.
Dirty Air Filter
- A clogged air filter can obstruct airflow and prevent the AC from heating efficiently. Clean or replace dirty filters as needed.
Refrigerant Charge Issues
- Just like with cooling, low refrigerant levels can greatly impact the Mr. Slim’s ability to heat a room. Have an HVAC technician inspect and recharge the refrigerant if low.
Heat Pump Failure
- If your unit has a heat pump, failure of this component can prevent warm air flow. A technician will need to diagnosis and replace a bad heat pump.
Pay attention to when the heating problems occur to help narrow down the issue. Many heating problems can be addressed with maintenance and minor repairs.
Troubleshooting Mr. Slim Remote Control Problems
Many Mr. Slim issues arise from problems with the infrared remote control used to operate the unit. Here are some potential remote control issues and solutions:
Remote Out of Range
- The Mr. Slim remote has a limited operational range. Make sure you are standing within 25-30 feet and pointing the remote directly at the indoor unit when pressing buttons.
Low or Dead Batteries
- Replace old batteries in the remote with fresh ones. Make sure batteries are installed correctly by checking polarity markings.
Wrong Remote Buttons
- Consult your owner’s manual to confirm you are pressing the correct power, mode, fan speed and temperature buttons.
Damaged Remote Control
- If the remote display is faint or buttons are unresponsive, the remote control unit itself may be faulty. Try resetting the remote and if issues persist, replacement remotes can be ordered online.
Faulty Indoor Unit Receiver
- In rare cases, the infrared receiver on the indoor unit may be damaged and prevent signal reception. A technician can diagnose and replace the receiver if needed.
Troubleshooting Mr. Slim Heat Mode Problems
If your Mr. Slim successfully provides air conditioning but has issues when running in heat mode, the following are some likely causes:
Power Supply Problems
- A blown fuse, tripped breaker, faulty wiring or outlet issue can disrupt power when the unit switches into heat mode. Check for these electrical problems and correct as needed.
Low Refrigerant
- Just as with cooling issues, low refrigerant levels can prevent the Mr. Slim from adequately heating. Have an HVAC technician inspect and top off the refrigerant charge.
Dirty Outdoor Unit
- Make sure to clear any debris around the outdoor condenser unit. Clogged air flow will impact heating performance.
Failed Heat Pump
- Heat pump failure is the most common reason a Mr. Slim cannot blow hot air in heat mode. A technician will need to diagnose and replace the faulty heat pump component.
Defective Reversing Valve
- A problem with the reversing valve, which switches the refrigerant flow for heating, can prevent warm air flow. Have a technician inspect this component.
Compare the heating and cooling performance to determine if the issue lies with the heating system specifically. In many cases the problem is electrical or refrigerant-related.
Troubleshooting Mr. Slim Compressor Problems
The compressor is the integral component responsible for pumping refrigerant through the AC system. If the compressor is faulty, the Mr. Slim may not cool, heat or turn on at all. Some compressor issues include:
Power Disruption
- A blown fuse or tripped breaker can cut power to the compressor. Restore electrical supply by replacing fuses or resetting breakers.
Low Refrigerant
- Operating the compressor with insufficient refrigerant can cause it to overheat and fail. Have an HVAC technician check the refrigerant level and recharge if needed.
Capacitor Failure
- The capacitor provides the jolt of power needed to start the compressor motor. A failed capacitor will prevent the compressor from turning on.
Compressor Motor Burnout
- If the compressor motor overheats frequently, it can permanently burn out and seize. The damaged compressor will need complete replacement.
Faulty Control Board
- Issues with the control board that governs compressor operation can prevent it from turning on. A technician will need to test and replace the control board if faulty.
Understanding Mr. Slim Blinking Light Codes
Mr. Slim units have indicator lights on the indoor unit that can blink in patterns to identify operational and error codes:
- Slow blinking light – This usually indicates a clogged air filter that needs to be cleaned or replaced. Slow blinking could also signify dirt buildup on the condenser coils.
- Fast blinking light – Fast blinking is most commonly caused by low refrigerant levels. An HVAC technician should be contacted to inspect for any leaks and recharge the refrigerant.
- Two blinks – Two consecutive blinks typically signals an issue with the outdoor unit such as a failed fan motor, disconnected wiring or damaged coil. A technician should diagnose and repair the outdoor unit.
- Three blinks – This points to an electrical malfunction like a short circuit, defective compressor overload, or problem with the control board. An experienced electrician can troubleshoot the electrical issue.
- Four blinks – Four blinks indicate a potential issue with the indoor unit itself. Some possibilities include faulty indoor fan motor, float switch malfunction or temperature sensor failure.
When to Call a Professional Technician
While this guide covers many common DIY fixes for your Mr. Slim, some problems require a trained HVAC technician to properly diagnose and repair. Issues like:
- Refrigerant leaks
- Electrical malfunctions
- Defective compressors
- Burnt-out fan motors
- Faulty control boards
Require specialized tools, testing equipment and expertise to address. Safety should always be the top priority when dealing with electrical and refrigeration systems. Improper handling of refrigerant gases can also result in large fines.
Here are some signs it’s time to call a technician:
- Unit repeatedly trips circuit breakers
- Loud noises or grinding sounds from unit
- Burning plastic smell from unit
- No power at all to indoor or outdoor units
- Frozen evaporator coils
- Remote diagnoses refrigerant leak or electrical issue
Investing in professional service and maintenance will extend the life of your unit and ensure safe, reliable operation. Be sure to follow all of the maintenance tips outlined in the Mr. Slim owner’s manual as well. Keep filters clean, clear outdoor unit debris, and have HVAC checkups done before peak cooling and heating seasons.
