A complex service call on a commercial multi-unit system
At AirGreen , we are regularly called to diagnose and repair large HVAC systems , including Mitsubishi Electric VRF (Variable Refrigerant Flow) installations.
This intervention took place in Ville Mont-Royal , in a recent commercial building where several Mr. Slim R410A units were installed in parallel to serve different offices. The client had reported an abnormal pressure alert on the central controller, accompanied by a partial loss of air conditioning on one of the floors.
Initial diagnosis: communication alarm and pressure imbalance
Upon arrival, our Mitsubishi certified technicians performed a VRF network analysis using our dedicated Mitsubishi Service Tool diagnostic tool .
Initial surveys indicated:
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Lower than normal suction pressure on a circuit line.
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High discharge temperature on another master unit.
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A U4 error code , indicating an intermittent loss of communication between the outdoor modules and one of the indoor boards.
These clues suggested both a refrigerant flow problem and a communication malfunction in the network.
Step 1: Inspecting connections and electronic boards
Our technicians opened the control panels to check the communication bus connections (cable 1-2) connecting the various VRF units.
A slight loosening of terminals was observed on a slave unit, causing sporadic interruptions in data transmission between modules.
We have :
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Cleaned and tightened all electrical terminals .
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Checked the continuity of the communication cable .
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Reset the central controller to restart the communication sequence.
Step 2: Checking the refrigeration circuit
Next, we took a full reading of the pressures and temperatures on the three external compressors.
One of the circuits had a load imbalance : a partial lack of R410A refrigerant.
We have :
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Performed a dry nitrogen leak test , confirming no active leaks.
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Rebalanced the refrigerant charge to Mitsubishi's exact specifications, adjusted to the nearest gram.
The goal: to synchronize the pressure and temperature of all modules to restore uniform performance of the VRF network.
Step 3: Recalibrate the VRF system
Once the circuit was balanced, we ran a recalibration self-test via the central controller.
This process, unique to Mitsubishi Electric systems, allows each indoor module to recognize the network configuration and optimize the refrigerant flow according to actual demand.
The test confirmed stable operation, without error codes, with perfect flow rate and temperature differential .
Step 4: Preventive maintenance and recommendations
We took advantage of the intervention to carry out a complete inspection of the system :
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Cleaning the filters of the outdoor units and clearing the heat exchange fins.
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Checking the tightness of the refrigeration connections throughout the network.
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Check fans and inverter motors for premature wear.
Our recommendations to the building manager:
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Schedule biannual VRF network maintenance , which is essential to maintain throughput synchronization and prevent communication alarms.
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Clean the internal filters every quarter to prevent pressure drops.
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Install reinforced mechanical protection around the outdoor units, without obstructing ventilation (the protective wooden wall will be adjusted for better air circulation).
Results: restored stability and optimal comfort throughout the building
After several hours of testing and adjustments, the Mitsubishi Electric Mr. Slim VRF system has regained its perfect balance .
All areas of the building now benefit from uniform cooling , without excess energy consumption or compressor overload.
The manager expressed his satisfaction: the network, previously noisy and irregular, now operates quietly and efficiently .
Our team also provided a comprehensive technical report documenting pressures, temperatures, and interventions, to ensure rigorous monitoring for future maintenance.
Why AirGreen is the trusted choice for VRF systems in Montreal
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Mitsubishi Electric and Fujitsu VRF certified expertise .
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Highly trained technicians in complex multi-unit architectures.
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Advanced diagnostic tools for centralized systems.
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Customized service for commercial buildings, high-end condos and institutional buildings.
AirGreen – Your professional HVAC partner in Montreal, Laval, Longueuil, on the North Shore and the South Shore.
We ensure the performance, reliability and durability of your Mitsubishi Electric VRF systems, no matter how complex the installation.