When a rooftop compressor refuses to start: an effective and preventive AirGreen intervention
During a service call in Rosemont–La Petite-Patrie , our AirGreen team was contacted by a building owner whose Gree wall-mounted heat pump installed on the flat roof of a commercial building had stopped responding. In the early hours of summer, the outdoor unit, exposed to direct sunlight, was no longer starting the compressor, leaving several offices without air conditioning.
Installation background and configuration
The building was equipped with several independent wall-mounted heat pumps , each connected to a Gree outdoor unit mounted on rubber anti-vibration mounts. The system is designed to provide efficient and quiet cooling in each office, while maintaining optimal energy consumption.
Technical diagnosis on the ground
Upon arrival, we immediately carried out:
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A visual inspection of the condenser : no apparent damage, but a slight accumulation of dust on the fins.
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An electrical check : power supply confirmed, but no voltage to the compressor when cooling is requested.
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A continuity test on the contactor and starting capacitors.
The verdict: A 45 µF main capacitor showed a significant drop in capacitance (measured at 17 µF), explaining the compressor's failure to start . This type of failure is common on units exposed to extreme thermal cycles, particularly on unshaded flat roofs.
Intervention and repair
After securing the power supply:
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We replaced the starting capacitor with a certified original Gree model.
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We cleaned the heat exchanger fins using a biodegradable cleaner to restore optimal heat exchange.
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A check of the high and low pressure switch was carried out to ensure the correct balance of the refrigeration circuit.
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Finally, we tested the complete startup sequence under load.
The compressor restarted without any anomaly, the pressure stabilized at 230 psi on high and 120 psi on low, and the air blown inside showed a temperature of 15°C , a sign of restored efficiency.
Result: restored performance and extended reliability
The client was able to regain immediate comfort in the offices upon completion of our work. We also installed a sealed junction box to better protect the electrical connections from rainwater infiltration, an often overlooked improvement in rooftop installations.
AirGreen Prevention and Advice
To avoid this type of recurring breakdown, we recommended:
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A biannual preventive inspection before peak seasons (summer and winter).
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Systematic checking of capacitors at each maintenance, because their degradation is progressive and imperceptible before failure.
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Installing a metal sun shield to reduce overheating of electronic components.
These simple actions can increase the life of the compressor and reduce costly emergency calls .
AirGreen Expertise: Reliability and Precision on Every Roof in Greater Montreal
At AirGreen , every service call is treated with the same rigor:
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Complete analysis of the refrigeration and electrical circuit.
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Use of calibrated measuring instruments to obtain accurate diagnoses.
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Photo documentation and temperature readings provided to the customer for complete transparency.
Our teams work on all types of flat and sloped roofs, whether for offices, businesses, condos or residential buildings . Our expertise covers major brands of heat pumps and air conditioners— Gree, Fujitsu, Midea, Sharp, Lennox, Trane and Bosch —across Greater Montreal , including Laval, Longueuil, the North Shore and the South Shore .
Conclusion
This intervention in Rosemont–La Petite-Patrie demonstrates the importance of regular maintenance of exposed rooftop HVAC systems . A capacitor failure may seem minor, but it can shut down an entire system and cause the compressor to overheat. Thanks to a quick and methodical repair , AirGreen allowed this company to resume operations in optimal comfort, while extending the life of its Gree equipment.
At AirGreen , our mission is simple: to ensure your comfort, your peace of mind and the long-lasting performance of your heating and air conditioning systems.