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Réparation d’une thermopompe murale Fujitsu à Saint-Lambert
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Repair of a Fujitsu wall-mounted heat pump in Saint-Lambert

A discreet breakdown in a difficult-to-access corridor

One June morning, our AirGreen team was contacted by a customer in Saint-Lambert , on Montreal's South Shore , regarding a Fujitsu wall-mounted heat pump system that was no longer blowing cold air upstairs. The unit, installed high up in a narrow hallway, had been operating normally the day before—until an error code appeared on the remote control.
This type of situation is common in multi-level homes: the Fujitsu heat pump serves multiple areas of the home, and when an indoor component stops responding, it is often a sign of a sensor or circuit board problem .

Initial diagnosis: a revealing error code

Upon arrival, we noticed an error code “U4” indicating a loss of communication between the indoor and outdoor unit . This type of failure can have several causes:

  • a damaged communication wire,

  • a loose connection,

  • or, more rarely, a faulty electronic card .

After removing the bottom cover of the Fujitsu wall unit, our technician noticed traces of moisture on the PCB , caused by condensation that has accumulated over time. A classic sign in high-rise installations, where hot air rises and condenses around electrical components.

Intervention: cleaning, repair and protection

The intervention took place in several methodical stages:

  1. Power cut and secure the access area at the top of the stairs.

  2. Removal of the main electronic board and visual inspection with a magnifying glass.

  3. Thorough cleaning of the board using a specialized dielectric solvent.

  4. Replacement of two oxidized connectors , then application of a protective silicone coating to prevent any further infiltration.

  5. Communication test between the wall unit and the Fujitsu outdoor compressor.

Once the card was replaced, communication was instantly reestablished. The fan restarted, and cold air began to circulate in the stairwell again, stabilizing the interior temperature at 22°C .

A typical case of neglected condensation

Fujitsu wall-mounted units , known for their reliability, can still develop this type of problem when installed in areas with a high temperature differential (for example, between an air-conditioned floor and a warm attic). Moisture condenses on internal components, especially if the condensate drain is partially blocked.

At AirGreen , we encounter this scenario regularly in Saint-Lambert, Brossard and Longueuil , in multi-level homes.
To avoid this situation, we recommend:

  • Have the condensate drain checked every spring .

  • Ensure good air circulation around the unit (avoid frames or furniture that are too close).

  • Schedule a complete professional cleaning every 18 to 24 months, including the internal housing and PCB board.

AirGreen expertise: rigor, precision and prevention

This intervention in Saint-Lambert illustrates AirGreen's philosophy well: never limit yourself to the symptom, but identify the root cause of the problem.
Our RBQ and CCQ certified HVAC technicians are trained to work on all Fujitsu series , including the LZ, RLX, and LMAS1 ranges.
We use only non-conductive cleaning products and original manufacturer parts, guaranteeing the safety and longevity of the system.

Result: comfort restored and device protected

The client was able to find consistent freshness throughout the entire floor as soon as our intervention was completed.
The quiet and efficient Fujitsu wall-mounted heat pump has resumed normal operation.
Thanks to the protective layer applied to the card, the risk of recurrence has been eliminated for several years.

Before leaving, our technician carried out:

  • a check of the blowing temperature ,

  • a leak detection test ,

  • and a check of the condensate drain flow rate .

Result: everything was in order, ready for an uninterrupted summer.

Conclusion

This repair of a Fujitsu wall-mounted heat pump in Saint-Lambert highlights the importance of preventative maintenance and early detection of signs of internal humidity.
At AirGreen , we offer a complete service covering Montreal, Laval, Longueuil, the North Shore and the South Shore , combining technical expertise and attention to detail.

Every service call is an opportunity for us to extend the useful life of your equipment and ensure your comfort—summer and winter.

Warning:
This article illustrates a typical real-life repair performed by AirGreen. Conditions may vary depending on the model and environment. Only certified technicians may work on internal electronic components.