A heat pump breaks down on a humid day: field diagnosis
One June morning in Pointe-Claire , on Montreal's West Island , a customer contacted us after noticing that their Haier wall-mounted heat pump refused to start. The outdoor unit produced no sound, while the indoor unit displayed an intermittent error code. At AirGreen , we know that this type of failure is often linked to an internal electrical problem or a faulty communication board .
The image received from the customer showed a disassembled outdoor unit , with access to the electrical connection box and a measuring manifold already connected for pressure control. This configuration directed us towards both an electrical and refrigeration check, to quickly identify the cause of the failure.
Step 1: Check voltages and communication
Our technician first checked the supply voltage at the circuit breaker and at the terminal block of the outdoor unit:
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240 V present between the main lines;
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no signal return between the indoor and outdoor communication terminals.
This finding suggested a loss of communication between the electronic boards . We therefore continued the diagnosis inside the control panel, measuring the continuity and resistance on the communication cable connecting the two units.
Result: the cable had an internal cut , probably caused by the wire being crushed during a previous maintenance operation.
Step 2: Inspection of the refrigeration circuit
While the power was off, our team also checked the R-410A refrigerant circuit using the connected manifold. Static pressures were within the normal range, indicating no refrigerant leaks . This confirmed that the problem was purely electrical , not mechanical.
We then replaced the three-core communication cable with an approved cable with reinforced insulation and a cross-section adapted to the requirements of the manufacturer Haier.
Step 3: Replace the internal fuse and perform a complete system test
Upon opening the main board (PCB), our technician noticed that the built-in fuse was also blown—a direct result of the short circuit caused by the damaged cable.
The intervention therefore included:
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Replacement of the main fuse 3A/250V ;
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Cleaning the connectors to prevent future oxidation;
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Checking the grounding wiring ;
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Soft restart of the system to test communication and compressor operation.
Upon powering up, the heat pump restarted normally. The communication lights remained stable, and the compressor started with a pressure build-up in accordance with the manufacturer's specifications.
Result: a restored system and a reassured customer
In less than an hour, the Haier system was fully operational . The customer was comfortable again and was impressed by the speed of the diagnosis. We also added additional protection to the communication cable , using an insulating sheath resistant to thermal variations and vibrations.
Finally, our technician recommended an annual AirGreen maintenance , which includes:
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a voltage and continuity check on the main connections;
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an inspection of electronic cards ;
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and a complete check of the refrigeration circuit to ensure constant performance.
AirGreen: experts in heat pumps Haier, Fujitsu, Midea, Gree and more
Thanks to our technical expertise and our methodical approach, AirGreen intervenes quickly on all types of electrical, communication or pressure failures linked to HVAC systems .
We serve Montreal, Laval, Longueuil, the North Shore and the South Shore , with certified technicians capable of diagnosing the most complex brands, including Haier, Trane, Fujitsu, Mitsubishi, Sharp, Zephyr and Midea .
Every service call is handled with precision and transparency, ensuring long-lasting repair and year-round comfort .
Similar problem?
Is your heat pump refusing to start or displaying an error code? Contact AirGreen today for a professional diagnosis on the North Shore, South Shore, or in Montreal.