A complete breakdown on a roof in the middle of Montreal summer
On a hot June afternoon, AirGreen was contacted by a Plateau-Mont-Royal client experiencing a complete air conditioning failure. His Polar Bear wall-mounted heat pump system , installed on the flat roof of his building, was no longer producing any cooling. The two outdoor units were silent, and the occupants felt stiflingly hot inside despite the remote controls being turned on.
Initial Inspection: Units Exposed to the Elements
When our technicians arrived at the site, they found two Polar Bear compressors installed side by side on a roof covered with a white membrane —typical of residential buildings in the Plateau. The units showed signs of wear: oxidized fins, slightly dirty casings, and communication cables exposed to the elements.
Before any manipulation, we checked the electrical safety using a multimeter . Result: no voltage on the power terminals of the two units. The problem therefore seemed to come upstream of the electrical circuit .
Step 1: Electrical diagnosis
Our specialists traced the power circuit from the main circuit breaker to the disconnect box located on the roof. The latter, damaged by temperature fluctuations and humidity, showed advanced internal oxidation on the contact terminals. This explained the loss of power to the two condensers.
We immediately replaced:
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The disconnect box is defective.
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The electrical cables are slightly charred.
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Time-delay fuses for circuit protection.
Once the repair was completed, power was restored and the compressors restarted simultaneously.
Step 2: Checking the refrigerant operation
Once the system was powered back up, we carried out a complete analysis of the refrigeration cycle :
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The fans were running normally.
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The working pressures were slightly lower than the nominal values.
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Discharge temperatures indicated a slight lack of refrigerant.
After detection using an electronic leak detector , we located a micro-leak on a flare fitting connecting a liquid line. A small amount of R410A refrigerant had escaped, reducing the overall efficiency of the system.
So we have:
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Re-seal the connection with new gaskets.
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Pulled a full vacuum on the circuit to remove any moisture.
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Recharged the system to Polar Bear specifications.
Step 3: Calibration and Cleaning
Taking advantage of the restart, our technicians carried out a thorough cleaning :
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Dusting the condensation fins.
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Checking the condensate drainage.
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Calibration of the temperature sensor on each indoor unit.
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Complete heating and cooling mode test.
The system returned to perfect performance, reaching a supply temperature of 8°C after 10 minutes of operation, and a constant air flow across both zones served.
Result: comfort restored and safety assured
At the end of the intervention, the client found a stable and comfortable indoor temperature . More importantly, the electrical safety of the HVAC system was restored, eliminating any risk of short circuits or future failures.
We have recommended biannual maintenance for this type of exposed flat roof installation, including:
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Inspection of wiring and connections.
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Cleaning the coils.
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Checking the refrigerant pressure.
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The application of a protective anti-corrosion coating on the fins.
The importance of rigorous maintenance on roof installations
Rooftop systems, as is often the case in the Plateau-Mont-Royal , are subject to extreme conditions: sun, rain, snow, and temperature variations. Without preventative maintenance, electrical failures and performance losses become inevitable.
At AirGreen, we have the expertise to repair, protect and optimize these installations in demanding urban environments.
Our teams respond quickly throughout Greater Montreal , including Laval, Longueuil, the North Shore and the South Shore , for all wall-mounted heat pump systems — Polar Bear, Fujitsu, Midea, Gree, Lennox, Zephyr, Trane , and many others.
Conclusion
This Polar Bear wall-mounted heat pump repair in Plateau-Mont-Royal demonstrates our ability to accurately diagnose complex problems, even on rooftop installations. Thanks to our methodical approach and attention to detail, the client regained optimal comfort and a secure installation, ready to face the hottest Montreal summers.
AirGreen – your expert in HVAC repair, maintenance and installation in Montreal and its surrounding areas.