An outdoor unit installed on a roof that had lost its cooling power despite a normal start-up
In Rivière-des-Prairies–Pointe-aux-Trembles, our AirGreen team was called for a wall-mounted heat pump repair where the outdoor unit was installed on a flat roof. The client contacted us after noticing a significant drop in cooling performance: the indoor unit started, the remote control responded, the fan blew, but the room no longer cooled as before. The system seemed to be working on the surface, but it ran much longer for a weak result, with an indoor temperature that remained uncomfortable during hot days.
On site, the installation image already gave several important clues: a compact mini-split type outdoor unit, installed on supports above a roofing membrane, with the coil visible behind the grille, refrigerant lines entering from the side, aging pipe insulation, and exterior screws showing signs of oxidation. This type of installation is common in certain areas of Montreal, especially when it is necessary to avoid cluttering a yard, side passage, or facade.
The device was a residential wall-mounted heat pump, probably with an approximate capacity of 12,000 to 18,000 BTU depending on the size of the outdoor unit and the observed configuration. The exact brand was not clearly visible in the photo, but the type of equipment and the required intervention were typical of a wall system used to heat and cool a main area of the house.
Symptoms reported by the client
The client explained to us that the heat pump was not completely off. This was precisely what made the problem more difficult to understand: the indoor unit would turn on, the outdoor fan would run, and no loud noise was heard. Yet, the comfort was gone. The air blown was slightly cool, but not enough to effectively lower the temperature.
The observed symptoms were as follows:
- weak air conditioning despite a low setpoint;
- much longer operating cycles than before;
- air blown less cold at the indoor unit;
- functional outdoor unit, but reduced efficiency;
- slight vibration at startup;
- refrigerant piping with deteriorated insulation;
- variable performance depending on the time of day;
- feeling that the unit was struggling during periods of intense heat.
This kind of situation can have several causes: lack of refrigerant, reduced heat exchange due to a dirty coil, weakened outdoor fan, faulty condenser, inaccurate temperature sensor, restriction in the refrigerant circuit, poor communication between the indoor and outdoor units, or installation exposed to excessive heat on the roof.
At AirGreen, we avoid jumping to conclusions about leaks or complete replacements. An effective HVAC repair requires checking the environment, electricity, refrigerant circuit, and airflow before recommending a solution.
Inspection of the outdoor unit on the roof
Access to an outdoor unit installed on a roof always requires a more careful inspection. On a flat roof, the unit faces particular conditions: intense heat in summer, snow accumulation in winter, direct sunlight, humidity, wind, dust from the membrane, and accelerated aging of exposed materials.
In this case, several visible elements caught our attention. The outdoor coil seemed relatively clear, but a layer of fine dust and residue was present in some areas. The refrigerant lines ran along the side of the unit, with insulation that was beginning to deteriorate. This insulation is important: it protects the lines against thermal losses, moisture, UV rays, and temperature fluctuations. When it cracks or detaches, the system can lose efficiency, especially in air conditioning.
We also observed the condition of the fasteners, supports, and cable routing. Some external screws showed signs of oxidation. This was not the main cause of the failure, but it indicated that the unit had been exposed to the elements for several seasons. On an elevated installation, this type of detail must be taken seriously, as vibration or a weakened fastener can eventually put stress on the refrigerant lines.
HVAC diagnosis: check airflow, electricity, and refrigerant
Our diagnosis followed a precise sequence. The goal was to understand why a heat pump that started normally was no longer producing sufficient cooling.
Checking the air conditioning request
We first confirmed that the indoor unit was properly sending the request to the outdoor unit. The system responded to the command, and the compressor started. This ruled out a simple problem with the remote control, operating mode, or indoor control. The fault was more likely related to the actual performance of the device.
Outdoor fan inspection
The outdoor fan was running, but a slight vibration was noticeable at startup. We checked that the blades were not blocked, the grille was not deformed, and nothing was rubbing against the motor. The fan was working, but its efficiency also depended on the condition of the coil. A fan can run properly while being unable to release heat if the coil is dirty or if the system lacks refrigerant.
Cleaning and inspection of the outdoor coil
The outdoor coil was inspected over its entire accessible surface. Although the unit did not seem completely blocked, fine dust and residues accumulated on the fins limited heat exchange. On a wall-mounted heat pump, this detail can make a big difference. In air conditioning, the outdoor unit must release the heat captured inside. If the coil does not breathe well, the compressor works harder, pressure increases, and efficiency decreases.
We carried out a technical cleaning suitable for a rooftop installation, avoiding damage to the fins and protecting the electrical components.
Refrigeration circuit inspection
After the mechanical and electrical inspection, we checked the behavior of the refrigeration circuit. The measurements indicated below-normal performance, with signs consistent with a partial refrigerant leak. It was not a complete system shutdown, but a loss of pressure sufficient to reduce the cooling capacity.
The investigation then focused on accessible fittings. In this type of installation, flare fittings, vibration zones, exposed sections, and line passages are areas to check carefully. A micro leak can develop slowly over several seasons, until the heat pump continues to run but no longer delivers the expected performance.
Identified cause: micro leak at the fitting and deteriorated refrigeration insulation
The diagnosis identified a weakness at a refrigeration line fitting, with signs consistent with a slow leak. The degraded external insulation also contributed to exposing the piping more to temperature variations and UV rays. The combination of partial refrigerant loss and reduced heat exchange explained the customer's symptoms.
This conclusion was important. The system did not need immediate replacement. The compressor responded, the indoor unit communicated, the fan worked, and the failure was due to a combination of repairable factors: slow leak, insulation to be redone, necessary cleaning, and a full functionality check.
Work performed by AirGreen
We carried out a targeted intervention to restore the heat pump's efficiency and secure the installation.
Reworking the refrigeration fitting
The problematic fitting was redone to eliminate the leak. This step must be done precisely: improper tightening, a poorly formed flare, or an imperfect surface can cause a new leak after a few weeks or months. Our technicians corrected the fitting following best practices, then performed the necessary checks to confirm its tightness.
Leak test and vacuuming
After fixing the fitting, the circuit was tested to ensure there were no detectable leaks. A vacuum was then applied to remove air and moisture from the circuit before restarting. This step is essential to protect the compressor and ensure stable operation. Recharging without proper vacuuming can reduce the equipment's lifespan.
Refrigerant recharge according to system needs
Once the circuit was validated, we adjusted the refrigerant charge according to operating parameters. The goal was not to add gas randomly but to restore a charge consistent with the device’s behavior. After this step, the blowing temperature improved and the system began to cool more efficiently.
Replacement of deteriorated insulation
The insulation of the refrigerant lines was redone in exposed areas. This correction improves performance, reduces thermal losses, and protects the lines against outdoor conditions. On a roof, this step is especially important because the sun and weather accelerate material degradation.
Coil cleaning and final check
The outdoor coil was cleaned to improve heat exchange. We then restarted the heat pump and observed a full cycle. The compressor operated more steadily, the outdoor fan expelled heat better, and the indoor unit produced cooler air. The client noticed a clear difference in the room’s comfort.
What this repair in Rivière-des-Prairies–Pointe-aux-Trembles shows
A wall-mounted heat pump installed on the roof can offer excellent efficiency, but its exposure requires more regular monitoring. In Rivière-des-Prairies–Pointe-aux-Trembles, as elsewhere in Montreal, Laval, Longueuil, on the North Shore and the South Shore, outdoor units face conditions that can accelerate the wear of fittings, insulation, and electrical components.
A loss of performance is not always a total breakdown
In this case, the heat pump was still starting. For many owners, this gives the impression that the system is working and that you just need to wait. However, a heat pump that runs for a long time without cooling properly can consume more energy, strain its compressor, and eventually break down completely. A quick intervention often allows the problem to be fixed before the damage becomes more serious.
Mistakes to avoid with a wall-mounted heat pump on the roof
Ignoring the insulation of refrigerant lines
Pipe insulation is not just an aesthetic detail. When it deteriorates, the system loses efficiency and the lines become more exposed to outdoor conditions. On a roof, it must be inspected regularly.
Adding refrigerant without repairing the leak
A recharge alone can give a temporary result, but if the leak is not fixed, the problem returns. In this intervention, the priority was to identify and fix the faulty connection before adjusting the charge.
Neglecting to clean the outdoor coil
A dirty coil reduces efficiency, especially in cooling. Even if the unit looks clean from afar, the fins can hold fine dust that limits heat exchange.
Forgetting that the roof increases stress
Heat accumulated on a roof membrane can be intense. An outdoor unit installed there must have good clearance, stable supports, and regular maintenance.
Final result: air conditioning restored and installation secured
At the end of the intervention, the wall-mounted heat pump had a more stable operation and better cooling capacity. The refrigeration connection was fixed, the circuit was tested, the charge was adjusted, the coil was cleaned, and the line insulation was redone. The client regained more consistent indoor comfort, with a system that cooled effectively again.
At AirGreen, we work on wall-mounted heat pumps, wall-mounted air conditioners, multi-zone systems, central heat pumps, and other HVAC equipment throughout Greater Montreal. Our approach is based on precise diagnostics, targeted repairs, and a clear explanation of the real cause of the problem.
A well-executed HVAC repair is not just about getting the unit running again. It must fix what caused the performance loss, protect the main components, and reduce the risk of recurrence. This intervention in Rivière-des-Prairies–Pointe-aux-Trembles is a good example: a system still repairable, but that needed a complete job on its refrigeration circuit, heat exchange, and external protections.