A sudden failure of hot air in the middle of a heatwave
One July afternoon, a customer in Outremont , Montreal, contacted us after noticing that their Mitsubishi wall-mounted air conditioner was blowing hot air despite the “Cool” mode being activated. The outdoor heat was exceeding 30°C and the apartment, located on the top floor of an old building, was quickly becoming uncomfortable.
At AirGreen , we know how quickly an air conditioning breakdown can disrupt daily life, especially in urban areas where natural ventilation is limited. Our team therefore went on site the same day to carry out a complete diagnosis of the HVAC system .
Initial inspection: a well-maintained device, but an invisible problem
The indoor unit, a wall-mounted Mitsubishi Electric model , was neatly installed in the living room, free of obstructions and excessive dust. The filters had been recently cleaned, indicating that the customer was following good maintenance practices. However, a slight dark spot on the ceiling suggested a possible condensation or hot air backflow problem.
We immediately checked:
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The operating mode on the remote control (confirmed in cooling mode)
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The set temperature (set to 21°C)
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Air flow (low despite the turbine being in operation)
Everything indicated that the external compressor was not starting.
Technical diagnosis: control board and communication interrupted
Using our measuring instruments, we confirmed that the signal between the indoor unit and the outdoor condenser was not being transmitted correctly. On wall-mounted Mitsubishi systems, faulty communication wiring or a faulty electronic board can prevent the compressor from starting, even if the indoor unit appears to be operating normally.
After removing the front cover, our technicians measured the voltage across the main connector. The result: the PCB no longer transmitted the start command. This failure is typical of devices exposed to voltage fluctuations or thermal wear of the electronic components .
Intervention: card replacement and complete calibration
We replaced the main control board with a genuine Mitsubishi Electric part, then performed:
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A check of the communication wiring between the two units;
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A compressor continuity test ;
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A complete system calibration using the built-in service mode.
Once the repair was completed, the compressor restarted normally and the blowing temperature dropped to 11°C at the outlet of the indoor unit , a sign of perfect performance.
Result: restored comfort and prevention of future breakdowns
The customer immediately felt the difference: a uniform and quiet flow of fresh air, typical of Mitsubishi Electric quality. Before leaving, we recommended:
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Installing a surge protector on the power line;
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A complete professional cleaning once a year;
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An R-410A refrigerant charge check every two years to ensure energy performance.
Thanks to this intervention, his Mitsubishi wall-mounted air conditioner is ready for several years of reliable comfort, ready to face the next heat waves.
AirGreen expertise serving Montrealers
At AirGreen , we are proud to be the HVAC reference in Greater Montreal, Laval, Longueuil, the North Shore and the South Shore . Our certified technicians work on all recognized brands: Mitsubishi, Fujitsu, Gree, Midea, Goodman, Sharp, Daikin , and many others.
Our promise:
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A quick and precise diagnosis , carried out on site;
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Original parts for every repair;
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A professional, transparent service that respects your space;
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Guaranteed interventions , whatever the type of system: wall-mounted heat pump, wall-mounted or multi-zone air conditioner .
In conclusion
This repair of a Mitsubishi wall-mounted air conditioner in Outremont demonstrates the importance of a thorough technical analysis before any unit replacement. A simple circuit board problem can interrupt the entire system's operation, but with AirGreen's experience, every fault can be resolved quickly, efficiently, and sustainably.