A compressor stopped: diagnosis of a complex electrical fault
A residential customer in Boucherville , on Montreal's South Shore , recently contacted us after noticing that their Fujitsu wall-mounted heat pump was no longer starting. There was no noise, no vibration—the system seemed completely inert. After several unsuccessful restart attempts, the customer decided to call AirGreen , a recognized specialist in residential HVAC system repair .
Our team quickly arrived on site for a complete electrical inspection of the outdoor unit.
Initial diagnosis: no voltage to the compressor
The first step was to check the power supply to the main board and the compressor. Using a Fluke 87V digital multimeter, we found a complete absence of voltage at the compressor terminal block , while the 240V input voltage was present at the main terminal.
This finding led our suspicions to a failure of the control board or the starter relay circuit .
Detailed checks: continuity test and resistance measurements
To confirm our hypothesis, we carried out several key measurements:
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Continuity check on compressor terminals (C, R, S) — resistance values were within Fujitsu specifications (approx. 1.5 / 3.8 / 5.3 Ω).
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Visual inspection of welds and connectors — no signs of burning or electric arcing.
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Start relay test : no activation voltage, confirming that the main electronic board was no longer controlling the start .
Thanks to a precise diagnosis, we were able to identify the exact source of the problem: a faulty power board following a power surge probably caused by a fluctuation in the network.
Intervention: replacement and recalibration of the electronic card
Our technicians carried out a complete replacement of the Fujitsu external PCB board , an original part supplied by the manufacturer. The operation included:
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Complete disconnection of internal wiring and systematic identification of each connector.
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Installation of the new card , with calibrated tightening of the terminals according to the recommended values (0.8 Nm).
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Reconnecting the temperature sensors and the communication module .
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Checking the inrush current at startup using the integrated current clamp (reading: 8.4 A, within standards).
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Complete operational test in heating and cooling mode.
Once the new card was installed, the heat pump came back to life instantly.
Optimization and prevention: protecting electronic components
In order to avoid a recurrence, we recommended to the client:
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Installing a dedicated HVAC surge protector , designed to protect the PCB and compressor from voltage fluctuations.
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Annual preventative maintenance including cleaning electrical connections and tightening terminals, particularly before the summer period.
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Adding a line filter to improve the stability of the current supplied to the heat pump.
Result: restored performance and assured reliability
After checking the pressures and temperatures, the Fujitsu heat pump demonstrated impeccable performance :
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Stable condensing pressure at 385 psi (R-410A).
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Blowing temperature at 46°C in heating mode.
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Rated power consumption at 6.1 A.
The system has returned to full efficiency, providing the residence with consistent, quiet, and energy-efficient comfort. The client was particularly pleased with the speed of diagnosis and the precision of the work carried out on a complex electrical fault.
AirGreen: Fujitsu expertise on the South Shore and throughout Greater Montreal
At AirGreen , we specialize in the repair, maintenance and installation of Fujitsu wall-mounted heat pumps , as well as many other renowned brands (Midea, Mitsubishi, Gree, LG, Lennox, Trane, etc.).
Our interventions cover all of Greater Montreal :
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South Shore : Boucherville, Brossard, Saint-Lambert, La Prairie…
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North Shore : Laval, Sainte-Thérèse, Terrebonne…
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Montreal : Plateau, Ville-Marie, Côte-des-Neiges and more.
Our certified technicians perform accurate and transparent diagnostics , using professional tools to ensure the performance, durability and safety of your HVAC systems.
Power outage? AirGreen responds with expertise.
Trust AirGreen for any electronic board, compressor, or HVAC control module repair . We bring your systems back to life with rigor, speed, and expertise.