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Appel de service pour une thermopompe murale Gree à Rosemont–La Petite-Patrie
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Service call for a Gree wall-mounted heat pump in Rosemont–La Petite-Patrie

An overheating compressor on a flat roof: a typical case of summer overheating in an urban environment

During Montreal's heatwaves, HVAC systems installed on flat roofs are subjected to extreme conditions: accumulated heat, limited air circulation, and direct exposure to the sun. At AirGreen , we were called to Rosemont–La Petite-Patrie , in the heart of Montreal, to diagnose a Gree wall-mounted heat pump installed on the roof of a residential building. The client reported that their system was no longer cooling and was emitting an unusual vibrating noise .

Initial diagnosis: a compressor exposed to heat and unstable voltage

Upon climbing onto the roof, our technician immediately noticed that the Gree wall-mounted condenser , installed on a concrete slab, was directly exposed to the sun without shelter or shade . The power cable showed signs of wear and overheating. Initial checks confirmed:

  • slightly unstable supply voltage due to an aging circuit breaker;

  • compressor overheating caused by lack of ambient ventilation;

  • and a buildup of dust and grit inside the condenser.

These conditions significantly reduced the heat exchange capacity of the system.

Step 1: Complete cleaning and inspection of the refrigeration circuit

We started by removing the top grille and blowing out the condensing coil with a jet of compressed air. Next, a neutral cleaner was applied to dissolve the thin layer of oil and dust that clogged the fins.
The refrigeration circuit was inspected using an electronic leak detector, confirming that no loss of R410A was present.

Step 2: Electrical Check and Power Stabilization

The rooftop electrical panel showed a slightly oxidized 15A breaker . We removed it, cleaned it, and temporarily replaced it with a CSA-approved 20A breaker , which was better suited to the Gree heat pump's rated load.
The electrical connections were tightened and a continuity test was carried out on the main power cable, ensuring a stable voltage of 238V .

Step 3: Test the Compressor and Condenser Fan

After the current had stabilized, we restarted the system and observed the behavior of the Gree rotary compressor . The measurements showed:

  • Low pressure: 115 psi

  • High pressure: 255 psi

  • Evaporation temperature: 8°C

  • Discharge temperature: 58°C

Slightly high values, typical of overheating due to thermal reverberation from the roof . To remedy this, we added a perforated aluminum thermal shading screen to limit the direct impact of solar radiation.

Step 4: Realign the ducts and optimize the airflow

The refrigerant pipes and electrical cables were lying directly on the roof gravel, exposed to significant thermal variations. We repositioned them in a rigid insulated conduit , raised using UV-resistant supports .
This modification reduces energy losses, protects the ducts from the sun and improves the safety of the installation.

Results: Restored performance and optimized efficiency

After two complete operating cycles, the system reached an indoor blowing temperature of 12.6°C , which is perfect performance for a Gree 12,000 BTU wall-mounted heat pump .
The compressor noise level returned to normal and the condensing air flow was smooth. The customer, located on the top floor of the building, immediately noticed a difference in comfort within minutes of the repair.

Preventative Tips for Flat Roof Installations

This case illustrates the importance of regular maintenance of outdoor units installed at height:

  • Annually check electrical wiring and circuit breakers exposed to the sun;

  • Install shading or heat shielding to reduce overheating;

  • Ensure that refrigerant lines do not rest directly on gravel ;

  • Clean the condenser coil at least twice a year, especially after pollen and heavy rain.

AirGreen Expertise: Serving Montreal’s Urban Buildings

Flat roof work , common in boroughs like Rosemont, Le Plateau, and Ville-Marie , requires specific expertise. Access, ground stability, cable management, and weather resistance are all parameters our technicians assess with every call.

Thanks to our experience, we guarantee not only the rapid repair , but also the longevity of each HVAC installation — whether it is a wall-mounted, multi-zone system or a VRF for a residential building.

Conclusion

This Gree wall-mounted heat pump repair in Rosemont–La Petite-Patrie demonstrates our meticulous and preventative approach.
At AirGreen , we operate throughout Montreal, Laval, Longueuil, the North Shore, and the South Shore to ensure long-lasting, optimized HVAC repairs. Each service has the same goal: restoring comfort, extending the life of the equipment, and improving its energy efficiency .