An early spring service call
In early March, just as the snow was melting, our AirGreen team was called to Sainte-Rose, Laval , for an urgent repair on a Fujitsu wall-mounted heat pump installed on the side wall of a brick house. The customer contacted us after noticing that their outdoor unit was no longer starting and that only the indoor fan was running—a typical sign of an electrical or communication problem between the two units .
The outdoor unit was mounted on galvanized wall brackets , slightly above the ground, a common choice to prevent snow and debris from accumulating during the winter. The installation, while compliant, was already showing some signs of aging: slightly worn ducts, exposed wiring sheath, and minor oxidation on the electrical connections.
Diagnosis: a faulty electronic card relay
Our technicians carried out a complete inspection of the Fujitsu system , starting with the most critical checks:
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Power supply check : stable voltage at 240V — compliant.
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Inspection of wiring between units : no visible breaks or shorts.
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Communication check via signal cable: intermittent signal, indicating a control problem.
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Analysis of the main electronic board : a compressor start relay showed traces of internal carbonization.
This relay, responsible for powering the compressor at startup, had stopped working properly, preventing any heating or cooling cycle. An accurate diagnosis made possible thanks to our specialized AirGreen measuring tools , capable of detecting internal continuity losses invisible to the naked eye.
Repair: Relay replacement and wiring revision
Once the problem was confirmed, we undertook the following repairs:
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Replacement of the Fujitsu electronic card relay with an original part.
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Thorough cleaning of the board using a dielectric solvent to remove carbon residue.
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Re-routing of control wiring in new sheathing for better protection against moisture.
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Reinstallation and reseal of exterior electrical connections with HVAC grade silicone to prevent spring infiltration.
Following these interventions, we carried out a gradual restart of the system. The compressor restarted immediately, reaching nominal pressures in a few seconds. Inside, the blowing temperature stabilized at 13°C in air conditioning mode , proof of the full return of the heat pump's performance.
Technical analysis: why this type of breakdown occurs
Fujitsu circuit boards , renowned for their reliability, can nevertheless be affected by repeated freeze/thaw cycles and winter voltage fluctuations . The relays, mechanical components inside these boards, eventually wear out, especially if the heat pump has been used intensively for heating for several consecutive winters.
Warning signs include:
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A clicking noise without the compressor starting ;
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The indoor fan that works alone ;
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Flashing lights on the indoor unit (error code FU or EE depending on the model).
Our technicians recommend having these cards inspected every 3 to 4 years , particularly in areas with harsh winters such as Laval, Montreal and the North Shore .
AirGreen Preventive Maintenance Tips
To avoid this kind of costly and uncomfortable breakdown, we recommend:
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Clear snow from the base of the outdoor unit to prevent moisture from entering the connections.
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Have the electronic board and relays checked during spring maintenance.
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Install an HVAC surge protector on 240V circuits to protect the heat pump from power surges.
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Avoid prolonged use of forced defrost mode without technical supervision.
These simple actions extend the life of the system and reduce the risk of heating or air conditioning interruptions during critical periods.
Result: comfort restored and customer reassured
At the end of the repair, the Fujitsu heat pump was working perfectly again. The customer, relieved not to have to replace the entire unit, was impressed by the speed of the diagnosis and the precision of the work carried out . We also scheduled a complete maintenance visit in the spring to ensure optimal performance before the warm season.
At AirGreen , our priority is to maximize the durability of HVAC equipment while ensuring transparent and reliable service. Whether in Laval, Montreal, Longueuil, on the North Shore or the South Shore , we offer the same rigor and attention to detail with every service call.
In summary:
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Problem detected: faulty relay on the electronic board.
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Solution: Replace the relay and rewire the control wiring.
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Result: Complete reboot and performance restored.
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Location: Sainte-Rose, Laval.
AirGreen , your trusted HVAC partner for the repair and maintenance of Fujitsu, Midea, Gree, Sharp, Lennox heat pumps and more, throughout Greater Montreal.