Emergency intervention on a snowy roof: AirGreen rigor at the service of collective comfort
At AirGreen , we know that HVAC breakdowns never take a break—especially in the depths of a Montreal winter. This service call came from a residential building in Côte-des-Neiges , where a Gree MultiZone system serving several apartments had stopped heating during a freezing weather. Our mission: to quickly diagnose and repair this complex installation on a snowy roof , while ensuring the safety and reliability of the system.
Background: A low-yield MultiZone system
The building, recently built and well-insulated, was equipped with several Gree MultiZone condensers installed in a row on the roof. Each unit supplied two to four indoor wall-mounted heat pumps. Occupants in several units reported a lack of heating for the past 48 hours. Despite active compressors, the ambient temperature remained at around 15°C , well below the expected comfort level.
The weather conditions were extreme: -18°C, heavy snow accumulation, and constant wind. Our technicians intervened in the evening with specialized equipment to secure the rooftop work area.
Diagnosis: An ineffective defrost cycle and a faulty control board
From the first inspection, several important observations were made:
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Accumulation of thick ice on the external exchangers ;
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Abnormally low evaporation temperatures;
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Main outdoor unit displaying error code “E6” — communication interrupted between master board and secondary modules;
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No trace of refrigerant leak, stable but inert pressures.
After checking with a Gree Service Tool communication analyzer , our technicians confirmed that the main control board (outdoor PCB) was faulty, preventing the automatic triggering of the defrost cycle. As a result, ice continued to build up on the coils, blocking ventilation and reducing the overall thermal capacity of the system.
Repair steps: a delicate operation on an icy roof
The conditions of the intervention made this repair particularly complex. The AirGreen team applied a rigorous method:
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Cutting off the main power supply and securing the work area;
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Manual defrosting of coils using a controlled heat gun to prevent damage to the fins;
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Complete replacement of the external control board with an original Gree part, delivered directly from our technical inventory;
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Reconnecting the communication wiring and synchronizing the MultiZone system;
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Functional test in extended heating mode (30 minutes) to validate the stability of the compressor and the correct operation of the automatic defrost cycle.
The team also took advantage of the intervention to tighten the refrigeration connections and check the crankcase heaters on all units—crucial maintenance in Quebec's winter climate.
Result: heat restored for the entire building
At the end of the intervention, the Gree MultiZone system returned to its nominal performance:
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Discharge pressure: 355 psi
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Suction pressure: 118 psi
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Indoor blowing temperature: 44°C
Tenants could feel the difference within the first few hours. The room temperature was stabilized in all affected apartments, and the property manager received a comprehensive technical report, including before/after photos and recommendations for preventive maintenance.
AirGreen Expertise: know-how and resilience in the field
Working on a snowy roof in Côte-des-Neiges , at night and below -18°C, requires more than technical know-how: it requires preparation, courage and a perfect mastery of HVAC safety protocols.
Our certified technicians work with Gree proprietary analysis tools and maintain a high level of proficiency on all major brands, including Fujitsu, Midea, Sharp, Goodman, Lennox, Zephyr, and Bosch .
Thanks to this expertise, AirGreen has become a trusted partner for the maintenance and repair of MultiZone systems in Montreal, Laval, Longueuil and on both shores.
AirGreen Tips for your MultiZone installations in winter
To avoid similar breakdowns, we recommend:
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A complete maintenance before the cold season , including cleaning the coils and testing the defrost sensors;
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A minimum clearance of 60 cm around each unit to allow good ventilation even in case of snow;
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Error code monitoring via the main remote control ;
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Annual maintenance by certified technicians , particularly for multi-unit buildings.
These simple actions help extend the life of MultiZone systems and ensure continued comfort, even during the harshest winters.
Conclusion
This repair on a Gree MultiZone system in Côte-des-Neiges perfectly illustrates AirGreen's philosophy: responsiveness, rigor, and local commitment . By restoring the heating of an entire building despite extreme conditions, our teams prove every day that excellent HVAC service relies as much on skill as on passion for the job.