A service call in a condominium building in Montreal
At AirGreen , we regularly work in apartment buildings in the Plateau-Mont-Royal , an area where HVAC installations must deal with restricted spaces and specific architectural constraints.
Recently, our team was commissioned to diagnose and repair a Daikin wall-mounted heat pump installed on the balcony of a modern red brick condo on the third floor of a typical residential building in the neighborhood.
The client, a young professional, had noticed a few days ago that his heat pump was no longer cooling the apartment effectively and that a flashing error code was appearing on the indoor unit.
Initial diagnosis: a heat pump that stops cooling
Upon arrival, we began by inspecting the outdoor unit on the balcony. The unit, a 12,000 BTU Daikin running on R-410A refrigerant, was clean, well-cleared, and mounted on anti-vibration mounts adapted to the balcony slab. However, a slight whistling noise could be heard when it was turned on—a classic sign of low pressure in the refrigeration circuit .
We continued the diagnosis inside and observed that the wall unit stopped after a few minutes, without producing cold air. A check of the Daikin error codes confirmed a message like “U4 – communication error” , often caused by a bad electrical contact or a voltage imbalance .
Step 1: Check the Wiring and Control Module
Our technicians removed the outdoor unit's cover to inspect the circuit board and communication connections. One of the connectors connecting the board to the compressor showed signs of oxidation due to moisture, likely caused by infiltration during a recent rain event.
We cleaned the connector with dielectric cleaner and replaced the damaged plug.
We then tested the supply voltage: 239 V stable — in line with Daikin specifications.
Step 2: Pressure test and inspection of the refrigeration circuit
Once contact was reestablished, we performed a static pressure test using electronic pressure gauges. The refrigerant level was slightly below the standard, suggesting a slow microleak .
We injected nitrogen at 300 psi and used a UV lamp and an electronic detector to locate the leak. It was coming from the flare connection of the liquid pipe , located behind the vertical formwork rising along the brick wall.
After tightening the fitting and replacing the gasket, we performed a complete vacuum of the system for 45 minutes and then recharged it with 850 g of R-410A , according to the manufacturer's technical data.
Step 3: Calibration and performance validation
Once the repair was complete, we restarted the heat pump in air conditioning mode .
The performance readings were perfect:
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Indoor blowing temperature: 11.6°C
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Suction pressure: 115 psi
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Discharge pressure: 385 psi
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Power consumption: 4.1 A
We also checked the operation of the automatic defrost and the communication cycle between the boards , confirming that the error code had disappeared.
Step 4: Maintenance tips for condominiums
Before leaving the premises, we advised the client and the condominium association on several good practices to extend the life of the heat pump:
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Clean the interior filters every four to six weeks.
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Avoid covering or obstructing the outdoor unit , especially on balconies where air circulation is restricted.
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Schedule annual preventative maintenance in the spring or fall to check gas charge, wiring, and pressures.
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Protect outdoor wiring with rigid, waterproof conduits, especially on walls exposed to the elements.
These simple precautions help avoid the majority of breakdowns observed on high-rise installations in urban buildings.
Final result: restored comfort and secure system
In less than two hours, our AirGreen team restored the Daikin heat pump in Plateau-Mont-Royal to optimal efficiency.
The device now operates silently, ensures stable cooling , and the customer enjoys perfect comfort in his condo.
This intervention illustrates the precision and rigor of our HVAC services: from electronic diagnostics to the repair of micro-leaks , every detail counts to guarantee lasting performance and a pleasant indoor climate all year round.
AirGreen: your HVAC partner in Montreal and on the North/South Shore
Our teams operate daily in all boroughs of Montreal , as well as in Laval , on the North Shore and the South Shore .
We repair and service all major brands— Daikin, Midea, Gree, Fujitsu, Sharp, Goodman, Lennox, and more—using the highest industry standards.
AirGreen is more than a repair service: it's a commitment to the quality, transparency and energy performance of your HVAC systems.