An intervention on a flat roof typical of Montreal buildings
On a beautiful summer day, our AirGreen team responded to a service call in the Rosemont–La Petite-Patrie neighborhood of Montreal regarding a Midea MultiZone heat pump installed on the roof of a multi-unit residential building. The client, an attentive homeowner, had noticed that several zones of his multi-split system were no longer producing the same cooling output, and that some indoor units were displaying intermittent errors.
Installed four years ago, this heat pump was used to cool three apartments located under the roof. This type of configuration, common in urban buildings, requires special attention to refrigerant distribution and the stability of the electronic system that controls the multiple indoor units.
Initial diagnosis: pressure imbalance and errors on the indoor module
Upon our arrival, our technician undertook a series of systematic checks :
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Visual inspection of outdoor units mounted on metal supports , securely fixed and clear for good ventilation.
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Checking the power supply and communication between the modules.
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Reading error codes on indoor units — signaling pressure imbalance and insufficient refrigerant flow to two out of three zones.
Using a digital manifold and an electronic scale , we quickly confirmed that the system was experiencing a slight loss of R-410A refrigerant , resulting in intermittent operation and uneven cooling in the apartments.
Step 1: Pressure test and locate the leak
Before any recharge, it was essential to check the complete leak tightness of the circuit . We isolated each refrigeration line serving the different indoor units, then injected dry nitrogen at 400 psi to identify the leak.
After 20 minutes of observation, the pressure in a single line decreased slightly—a clear clue. We then used an electronic leak detector to confirm the presence of a microleak at a poorly sealed flare on a small-diameter line.
This type of defect, often caused by repeated thermal expansion or insufficient initial tightening , can go unnoticed for years before causing a general imbalance in the MultiZone system.
Step 2: Repair the connection and apply a vacuum
Once the leak is located, we have:
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Disconnected the affected fitting and replaced the flare nut .
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Cleaned the contact surfaces using a cooling solvent .
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Tighten the assembly with a calibrated torque meter to ensure a perfect seal.
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Reinjected with nitrogen for an extended 45 minute pressure test .
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Observed perfect stability at 400 psi , a sign that the leak was completely resolved.
The circuit was then placed under complete vacuum down to -30 inHg for 45 minutes in order to eliminate all traces of humidity, an essential step before recharging the refrigerant gas.
Step 3: Recharging and balancing the MultiZone system
We then recharged the heat pump using a new bottle of R-410A , following the exact quantity indicated on the Midea nameplate: 3.8 kg for the complete system .
The operation was carried out by electronic weighing , guaranteeing perfect precision for the proper functioning of all areas.
Once charging was complete, the system was restarted and each indoor unit was tested individually.
The observed pressures, temperatures and electrical currents corresponded to the manufacturer's nominal values:
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Stable suction pressure: 120 psi
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High balanced pressure: 360 psi
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Average overheating: 8°C
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Subcooling: 10°C
Step 4: Complete validation and final adjustments
After 30 minutes of operation, all indoor units were blowing air at 7°C , confirming that the system had returned to optimal efficiency.
We also took advantage of this visit to:
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Insulate and reposition refrigeration lines exposed to UV.
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Check the electrical connections in the control box.
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Clean indoor unit air filters to maximize circulation.
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Reprogram the central communications system to prevent future synchronization errors.
The client particularly appreciated our rigor and attention to detail, noting that the system had never worked so well since its initial installation.
Result: restored performance and perfect comfort in all areas
Thanks to this intervention, the Midea MultiZone heat pump has regained its full power. All three zones of the building now cool evenly, without abnormal noise or interruptions.
The owner can once again count on optimal comfort and maximum energy efficiency , even during periods of intense heat.
AirGreen Recommendations: Maintenance and Prevention
Our technicians advised the client to schedule a comprehensive annual maintenance to prevent pressure imbalances and micro-leaks, particularly on MultiZone systems installed on flat roofs.
Recommended checkpoints:
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Checking operating pressures and temperatures.
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Inspection of flare fittings and refrigeration insulation.
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Cleaning the outdoor coils.
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Check condensate drain and wiring.
Regular monitoring helps maintain compressor durability and avoid costly long-term efficiency losses.
AirGreen: expertise, reliability and precision serving Montreal comfort
At AirGreen , every service call is handled with the same technical rigor.
Our teams operate throughout Montreal, Laval, Longueuil, on the North Shore and the South Shore , for the maintenance, repair and installation of residential and commercial HVAC systems.
Whether it's Midea, Fujitsu, Gree, Lennox, Zephyr, Goodman, Bosch or Sharp , our certified technicians ensure accurate diagnosis, long-lasting repairs and guaranteed performance .