Complex diagnosis on a commercial roof in Saint-Laurent
At AirGreen , our HVAC repair team was recently called to work on a Midea central heat pump installed on the roof of a commercial building in Montreal 's Saint-Laurent district. The customer contacted us after noticing a complete breakdown of the air conditioning system , a critical problem during a hot weather event.
Symptoms observed by the client
The building manager had noticed that:
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The outdoor fan no longer started.
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The compressor remained silent, without any vibration or start-up.
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The electrical panel on the roof showed a stable 240V power supply .
Given these signs, everything pointed to an internal electrical problem with the outdoor unit.
Detailed inspection of the heat pump
Once on site, our technicians carried out a complete analysis of the electronic circuit and the compressor .
The Midea unit, with a capacity of 36,000 BTU , had direct access to the main control board located in the upper compartment of the condenser. After opening, several observations were made:
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Presence of corrosion residue on the control board.
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No control voltage at the main fan terminal.
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Thermal fuse intact, but several suspect solder joints on the power section of the board.
Using a digital multimeter and a clamp-on ammeter , our technicians confirmed that the power supply circuit board (PCB) was no longer properly distributing voltage to the fan motor.
Checking the fan motor
We then isolated the fan motor in order to test it directly:
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Correct resistance between windings.
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No short circuit to ground.
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External boot test successful.
The engine was therefore not the cause - the fault was indeed with the main electronic card .
Replacing the control board
We completely replaced the main PCB with an original Midea module from our certified stock. Prior to installation, the connectors were cleaned and protected with a dielectric coating to prevent future oxidation, which is particularly important in exposed environments such as rooftops.
Once the card is replaced:
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The fan started spinning normally again.
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The compressor started without any faults.
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The operating pressures , measured with our electronic manifold , stabilized within the expected values: 120 psi at low pressure and 350 psi at high pressure in air conditioning mode.
Calibration and final checks
Our technicians then carried out a check of the compressor inrush current and the total consumption of the system:
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11.2 A on line L1,
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11.0 A on L2,
which perfectly matched the manufacturer's specifications.
A calibration of the outside temperature sensor was also carried out to ensure optimal regulation of the defrost cycle during the winter period.
Results and customer satisfaction
In less than two hours, the system was back up and running at full capacity , restoring the building's climatic comfort . The manager particularly appreciated:
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The speed of diagnosis ,
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Transparency of the technical report ,
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And immediate availability of genuine Midea parts through our authorized distribution partnership.
AirGreen Recommendations
To prevent this type of breakdown from recurring:
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Perform an annual preventive inspection including cleaning of the electronics compartment.
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Regularly check condensation drains and wiring insulation level .
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Protect exposed circuits with an anti-corrosion sealant when the condenser is installed on a roof.
AirGreen Expertise
This intervention perfectly illustrates our expertise in the repair of complex HVAC systems in commercial environments. Thanks to our experience with Midea, Fujitsu, Gree, Zephyr, Lennox and Mitsubishi heat pumps , we ensure a fast, rigorous service that complies with the manufacturer's standards .
At AirGreen, we know that an air conditioning shutdown in the middle of summer can have an immediate impact on comfort and productivity . That's why we do everything we can to offer sustainable and safe solutions , with complete traceability of parts and interventions.