When a silent breakdown reveals a hidden electrical problem
At AirGreen , our technicians often encounter discreet but critical breakdowns on residential HVAC systems. This was the case in Longueuil , on the South Shore of Montreal, during a service call for a Fujitsu Halcyon wall-mounted heat pump installed on a wooden balcony. The customer, surprised by a complete shutdown without any visible error message, initially thought it was a simple power outage.
First inspection: a unit at a complete standstill
Upon arrival, we found the indoor wall unit powered off and the outdoor compressor inactive. The customer mentioned that the system had suddenly shut down the day before, with no automatic restart. Upon examining the system, we noticed a few telltale signs:
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The communication wires between the two units appeared to have been partially exposed to the elements.
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The outdoor compressor , although in good general condition, showed signs of accumulated moisture.
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The unit was positioned on an enclosed balcony , limiting air circulation and increasing the risk of condensation.
Diagnosis: Communication failure between units
After testing the power supply, we confirmed that power was reaching both modules. The problem was therefore caused by a communication fault between the indoor and outdoor unit—a common problem on Fujitsu systems, often linked to:
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A damaged or oxidized connecting cable ,
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A poorly insulated connector exposed to moisture,
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Or a faulty control board (PCB) .
Using our multimeter, we detected an intermittent voltage drop on the communication line, confirming a loss of signal between the boards.
Intervention: replacement of the communication cable and testing of the circuit
We therefore undertook a complete replacement of the communication cable with a 4-conductor shielded wire, certified for outdoor use and UV resistant. This step required:
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Complete disconnection of the terminals on both units.
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Secure routing of the new cable through the wall passage, with waterproof sheathing.
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Reprogramming the communication code on the internal Fujitsu board, to ensure stable reconnection.
Once the new cable was installed, we restarted the system. The heat pump restarted normally, resuming its heating cycle with immediate response time and perfect voltage stability .
Complete performance check
To ensure performance after repair, we have carried out several checks:
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Indoor blowing temperature : 44°C after 8 minutes.
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R-410A refrigerant pressure : meets manufacturer's specifications.
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Operating current : stable at 5.6 A in heating mode.
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Sound level : standardized, without vibration.
The customer immediately noticed the return of heat and the usual silence of the Fujitsu Halcyon system—proof that replacing the cable had resolved the fault without the need for a major component replacement.
Prevention and recommendations
To avoid this type of breakdown, we recommended:
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Avoid unprotected extensions or junctions between units.
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Protect exposed cables with a water and sun resistant sheath.
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Schedule annual maintenance , especially for installations on balconies or terraces where humidity accumulates more easily.
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Ventilate the area around the condenser , as poor air circulation can affect defrosting and compressor longevity.
AirGreen expertise in the service of sustainable comfort
At AirGreen, our priority is to bring HVAC systems back to life with precision, transparency, and efficiency. This repair in Longueuil illustrates our approach: quickly diagnosing the root cause of a breakdown, replacing only the necessary components , and ensuring long-lasting performance at no unnecessary cost to the customer.
Our certified technicians work every day on Fujitsu, Midea, Gree, Sharp and Mitsubishi systems throughout the greater Montreal area, Laval , the North Shore and the South Shore , with the same technical rigor and the same attention to detail.