Urgent intervention on a flat roof in the rain
One particularly rainy June morning, our AirGreen team was called for a service call in Côte-des-Neiges–Notre-Dame-de-Grâce , Montreal. The client, the owner of a residential building, reported that his Fujitsu wall-mounted heat pump had stopped working the day before. During a period of humid heat, the problem had to be resolved quickly to avoid discomfort for the occupants.
The outdoor unit, installed on the building's flat roof , already posed a logistical challenge due to its limited access and the weather conditions. Despite the rain, our technician carried out a complete inspection of the system, respecting all necessary safety measures.
Initial diagnosis: lack of communication and complete shutdown
From the very first tests, one thing became clear: there was no communication between the indoor unit and the outdoor compressor. The Fujitsu module was no longer responding, and the operating indicator light was flashing in an error sequence —a typical signal of a faulty electronic board or a power supply problem.
Our checks allowed us to quickly rule out minor causes:
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Stable input voltage at 230V.
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Fuses intact.
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No apparent leaks or obstruction of the coils.
The analysis therefore focused on the main control board , located in the electrical compartment of the outdoor unit.
Thorough inspection and damage assessment
Upon opening the control panel, we observed evidence of moisture and light corrosion around the connectors. Although protected, the board showed signs of premature wear due to exposure to freeze-thaw cycles and water infiltration during heavy rains.
Using a multimeter and a handheld thermal imaging camera, our technician confirmed:
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No compressor control signal .
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Overheated MOSFET section on the circuit board.
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Partial short circuit between the power module terminals.
Verdict: The main control board was faulty.
On-site repair and long-lasting solution
To avoid prolonged system downtime, we replaced the electronic card with an original Fujitsu part , compatible with the AOU12RLS3H series, widely used in Montreal residential installations.
The stages of the intervention were carried out with rigor:
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Safe power cut and complete system disconnection.
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Removing the damaged card and cleaning the terminals.
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Installation of the new module with reinforced dielectric protection.
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Checking voltages and communication signals between units.
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Power up and complete functional tests.
Once the installation was complete, the heat pump restarted without incident. The compressor started normally, and cold air flow was restored within minutes.
Preventive measures and recommended maintenance
After the repair, our technician discussed with the customer several preventative measures to apply to extend the life of his system:
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Install surge protection to prevent electrical damage from thunderstorms.
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Regularly check the tightness of the electrical box , especially on roof installations.
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Schedule an annual AirGreen service to clean coils, check pressures, and inspect electronic boards.
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Keep cables well insulated and secured to avoid mechanical wear caused by wind.
These simple but essential recommendations help avoid costly breakdowns and ensure the long-term reliability of your Fujitsu system.
Result: a refurbished Fujitsu system
Thanks to our rapid and methodical intervention, this client's Fujitsu wall-mounted heat pump in Côte-des-Neiges–Notre-Dame-de-Grâce has regained full performance. The system was tested in both heating and cooling modes , demonstrating perfect efficiency in both cycles.
The owner, satisfied with the service, also chose to add an annual AirGreen maintenance contract , a wise decision to preserve the reliability of his device in the Montreal climate, which is often demanding for HVAC systems.
AirGreen: Fujitsu systems experts throughout Montreal
Fujitsu HVAC systems are among the most efficient on the market, but their maintenance requires specialized expertise. At AirGreen, we are Fujitsu certified technicians and operate throughout Greater Montreal, Laval, Longueuil, the North Shore and the South Shore .
Whether it's an electronic failure, a faulty compressor or a communication problem , we have the equipment and genuine parts needed to repair your system quickly, efficiently and sustainably.