A power outage in the middle of the hot season
As a period of intense heat approached, a homeowner in Sainte-Julie , on Montreal's South Shore, contacted us urgently about a Fujitsu wall-mounted heat pump that had suddenly stopped working. The unit, renowned for its reliability, no longer responded to commands, either from the remote control or via the wall panel. At AirGreen , we know that a breakdown of this type can quickly compromise the comfort of an entire home—we had to act quickly and precisely.
First step: a complete electrical diagnosis
Upon our arrival, our team conducted a complete analysis of the indoor unit's electrical circuit . This type of heat pump is equipped with a main circuit board that manages communication between the various modules—the fan motor, temperature sensors, and the outdoor compressor.
We immediately noticed:
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No power on the main terminal of the printed circuit board.
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A smell of burning component near the connection box.
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Traces of overheating on a neutral connection terminal.
These signs pointed us towards a problem with a damaged electronic card or poor connection tightening , a classic on older or poorly maintained units.
The cause: poor contact on the power terminal block
After disconnecting the main power supply and opening the control box (visible in the photo), our technicians confirmed that the power terminal block had a slight play on the neutral cable (white wire). This poor contact had led to progressive overheating , causing partial deterioration of the electronic board .
This type of problem is insidious: the heat pump can operate normally for weeks before suddenly shutting down without restarting. The danger, if not corrected quickly, is that it could cause a short circuit that could damage the outdoor compressor.
Control Board Repair and Replacement
Our intervention took place in several stages:
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Complete removal of the damaged electronic card .
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Cleaning the compartment using a dielectric spray to remove carbon residue.
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Replacement of the terminal block and defective connection lugs with new terminals with reinforced crimp.
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Installation of a replacement Fujitsu control board , calibrated to the exact model of the heat pump.
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Reconnection and complete functional test in heating and air conditioning modes.
Once the card was installed, we reset the system and observed a smooth and stable restart . Communication between the indoor unit and the outdoor condenser was immediately restored, confirming that the fault was indeed with the initial electronic module.
Prevention and recommendations
This case perfectly illustrates the importance of regular maintenance of electrical connections in HVAC systems. Thermal expansion and contraction cycles can, over time, slightly loosen connections , creating resistance and eventually heating the terminals.
Our technicians systematically recommend during each maintenance:
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Tighten all connections on the main terminal block.
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Visually inspect the electronic board for any heat marks.
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Check capacitors and relays before they cause a complete shutdown.
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Clean the coil and condensate tray to maintain stable performance.
A reassured customer and a heat pump ready for summer
After our final inspections, the Fujitsu wall-mounted heat pump regained its full cooling and heating capacity. The customer immediately felt the difference: cooler air, quieter operation, and a responsive control panel.
We also took the time to install an HVAC surge protector to protect the new electronic module from power surges—a small investment that can prevent costly future repairs.
At AirGreen , we work every day on electrical, electronic, and mechanical breakdowns of all brands of wall-mounted heat pumps throughout Montreal, Laval, Longueuil, the North Shore, and the South Shore . Our approach is based on rigor, transparency, and attention to detail—because an accurate diagnosis is always the key to a lasting repair.