An unexpected breakdown on a reliable and efficient heat pump
At AirGreen , we were recently called upon to repair a Mitsubishi Electric wall-mounted heat pump in the Outremont neighborhood of Montreal. The client, who owns a typical brick house in the area, had noticed that his system had not been heating adequately for several days, despite the indoor unit operating normally.
Installed on a flat, gravel-covered roof, the outdoor unit enjoyed good ventilation but showed several signs of wear related to Quebec's harsh seasons: damaged insulated pipes , exposed fittings , and debris accumulated around the condenser. These often overlooked elements can affect the overall performance of the HVAC system and cause intermittent outages.
Diagnosis: A communication problem between the units
Our certified technicians began the intervention with a complete diagnosis using a Mitsubishi Electric system analyzer . The error code displayed on the control module indicated a loss of communication between the indoor unit and the outdoor compressor , a common failure caused by:
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A corroded electrical connection in the communications cable.
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Cracked insulation allowing moisture to penetrate.
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Unstable voltage due to a slightly weakened circuit breaker.
We therefore undertook a continuity check of the wiring , then a voltage test between terminals L1, L2 and S. The voltage fluctuated abnormally, confirming the initial diagnosis.
Repair Steps
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Replacing the 14/3 communication cable :
We removed the old damaged cable, oxidized by temperature variations, and installed a new cable protected by a flexible UV-resistant sheath. -
Renovation of refrigerant insulation :
The refrigerant lines have been carefully re-insulated using high-density foam to prevent heat loss and condensation. -
Checking the compressor and gas pressures :
Our technicians then connected an electronic pressure gauge to check the suction and discharge pressures. The measured values confirmed that the Mitsubishi compressor was functioning properly once communication was reestablished. -
Cleaning and securing the condenser :
We removed leaves, dust and small debris accumulated on the gravel around the condenser to ensure better airflow.
Performance test and final calibration
Once the system was restarted, the heat pump resumed its heating cycle without any alerts. R-410A refrigerant pressures stabilized, and the indoor discharge temperature reached 42°C in heating mode , confirming optimal performance.
We also measured:
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Normal power consumption .
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Stable communication between electronic cards .
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An outside temperature automatically compensated by the integrated sensor , demonstrating that the Mitsubishi Electric inverter logic was working perfectly.
Prevention Tips for Flat Roof Heat Pump Owners
Heat pump installations on gravel roofs , such as in Outremont, present some unique challenges:
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Exposed cables are more vulnerable to weather and UV rays.
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Gravel accumulates heat , which can increase the condenser suction temperature.
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Organic debris (leaves, branches) can interfere with the fan's airflow.
At AirGreen, we recommend:
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A visual inspection at each change of season .
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Annual cleaning of the condenser .
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Renewal of the insulation of refrigeration pipes every 3 to 5 years.
Result: performance and peace of mind restored
The customer immediately noticed a difference: the Mitsubishi Electric heat pump was operating at full efficiency, without any error flashes or cycle interruptions. With this intervention, we not only restored heating, but also prevented a major failure that could have damaged the main circuit board.
This intervention once again demonstrates AirGreen's rigor and expertise in HVAC system repair in Montreal , particularly on high-end models such as Mitsubishi Electric , recognized for their reliability and exceptional performance in the Quebec climate.
We work every week on similar installations in Montreal, Laval, Longueuil, the North Shore and the South Shore , always with the same approach: precise diagnosis, transparency, and work carried out according to the strictest standards.