A service call in the middle of the cold season
At AirGreen , we know that a faulty HVAC system can quickly disrupt a home's comfort, even in winter. With this in mind, we were called to intervene in a charming duplex in Montreal's Rosemont–La Petite-Patrie neighborhood, where a Fujitsu wall-mounted air conditioner had been neither blowing hot nor cold air for several days.
The customer, concerned about seeing his unit blinking without ever starting the compressor, asked us to diagnose the fault before the arrival of the warm season. We dispatched one of our certified technicians for a complete inspection of the indoor and outdoor unit .
Diagnosis of the problem: a drifting sensor and an electronic card involved
The Fujitsu wall unit, installed near the ceiling of the hallway leading to the bathroom, appeared intact at first glance. No unusual noise, no visible damage. However, the error light was flashing in a triple sequence , a code well known to Fujitsu technicians indicating a communication anomaly between the indoor and outdoor boards .
Step 1: Check Voltage and Signals
Using our digital multimeter, we first confirmed the presence of a stable 230V voltage at the outdoor condenser terminal. There were no power supply issues to report.
We then checked the communication signals between the two boards. The signal wire showed irregular oscillations—a clue that the internal circuit board was probably faulty .
Step 2: Inspect the ambient sensor
At the same time, the room temperature sensor was returning an inconsistent reading: 8°C in a room with an actual 21°C. This discrepancy prevented the unit from properly modulating the fan and starting the compressor, forcing the system into a safety shutdown.
Step 3: Solution Applied
We replaced the faulty sensor and the indoor control board , then recalibrated the communication between the two modules. Once the system was restarted, the air conditioner restarted normally, blowing a constant stream of warm air at 35°C at the outlet.
Maintenance and prevention: our AirGreen recommendations
Fujitsu systems are renowned for their durability, but like any HVAC unit, they require regular maintenance to ensure optimal performance. We advised the customer to:
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Clean air filters every two months, especially during periods of heavy use.
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Check the indicator lights and contact a technician as soon as an error code appears.
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Have the electrical connections and control board inspected once a year.
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Avoid blocking air vents to ensure good circulation.
These simple actions extend the life of the unit while reducing energy consumption.
AirGreen: a professional service in Montreal and beyond
This repair perfectly illustrates AirGreen 's mission: to offer fast, transparent and sustainable service for each customer, whether it's a simple leak, a faulty sensor or an electronic card to replace. Our technicians operate throughout Greater Montreal , including Laval , Longueuil , the North Shore and the South Shore .
With our expertise in major brands— Fujitsu, Gree, Sharp, Midea, Bosch, TCL, and Hitachi —we guarantee accurate diagnostics and reliable repairs, in line with manufacturer recommendations.
End result: comfort restored and performance restored
At the end of our intervention, the client found a functional and quiet Fujitsu system, ready to ensure their comfort for several seasons. The indoor temperature was once again stable, without fluctuations or unwanted noise.
This success confirms once again that, at AirGreen, each intervention is guided by attention to detail, technical rigor and customer satisfaction .