A Mr. Slim system in trouble in the heart of a hot summer on the North Shore
At AirGreen , we recently received a service call in Blainville , on the North Shore of Montreal , regarding a Mitsubishi Electric Mr. Slim wall-mounted heat pump (R410A) that was no longer maintaining a stable temperature. This type of unit, known for its reliability, was showing signs of fatigue after several seasons of intensive use.
The customer noticed that the heat pump was blowing lukewarm air in cooling mode , despite the temperature being set well below the ambient temperature. In addition, the outdoor fan seemed to run intermittently , causing a noticeable drop in performance.
Complete diagnosis: an underperforming system due to several combined causes
Our AirGreen certified technician conducted a methodical inspection of the Mitsubishi Electric Mr. Slim system, inverter model with R410A refrigerant . Several abnormal elements were identified:
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Accumulation of dust on the condenser , reducing the heat exchange capacity.
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Refrigerant pressure slightly lower than manufacturer's specifications.
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Partially oxidized power wiring in the outdoor junction box, likely caused by moisture and freeze/thaw cycles.
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Partially blocked drainage , resulting in water marks on the wall near the indoor unit.
Each point, although minor individually, together contributed to a significant slowing of the thermodynamic cycle .
Repair steps: a complete and preventive intervention
1. Electrical check and cleaning of the condenser
After securing the power supply, we cleaned the condenser fins using a biodegradable product designed for residential HVAC units. The fan and motor were then tested and lubricated to ensure smooth operation.
2. Rewiring and junction protection
The oxidized connections have been replaced with new terminals protected with self-fusing tape and a waterproof insulating cap . This will prevent any water infiltration and extend the life of the electrical connection.
3. Checking the R410A refrigerant level
Using a digital manifold , we measured the refrigeration circuit pressures. Accurate top-up of R410A refrigerant was performed according to the manufacturer's recommendations. Evaporating and condensing temperatures returned to normal, confirming the system's stability.
4. Drain maintenance and indoor module calibration
The indoor unit was opened to clean the condensate tray and drain pipe . We also calibrated the temperature sensor and checked the communication between the indoor and outdoor electronic boards.
Result: restored comfort and optimal performance
At the end of the intervention, the heat pump was blowing air at 7°C at the indoor outlet , compared to 15°C before the repair. The compressor current stabilized, and the inverter cycle resumed smooth modulation, a sign of a return to full efficiency.
The customer immediately noticed an improvement in interior comfort and a reduction in exterior noise . A thermal inspection using an infrared camera confirmed an even distribution of heat across the exchanger, demonstrating balanced operation.
AirGreen Recommendations for Mr. Slim System Owners
Mitsubishi Electric Mr. Slim heat pumps are excellent HVAC systems, but their longevity depends directly on regular maintenance. We recommend all our customers to:
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Have the coils and filters cleaned twice a year;
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Check exterior wiring after each winter;
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Monitor for signs of abnormal condensation near the indoor unit;
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Schedule an annual professional maintenance before the warm season.
AirGreen: the benchmark in HVAC service on the North Shore and beyond
Every AirGreen intervention is guided by our commitment to quality, transparency, and sustainable performance . Whether you're in Blainville, Laval, Longueuil, or Montreal , our team ensures every Mitsubishi, Fujitsu, Midea, or Gree system operates at its peak potential.
Your comfort is our mission — and your trust, our greatest reward.
AirGreen — experts in Mitsubishi Electric wall-mounted heat pumps in Montreal, Laval, Longueuil and on both shores.