In a condo in Rosemont–La Petite-Patrie (Montreal) , our AirGreen team was called in to address a Tosot wall-mounted heat pump that was no longer providing the expected comfort. The client described a very typical situation: weak airflow , a feeling that the unit was "working hard" without actually cooling, and sometimes a musty odor upon startup. With this type of unit, the cause can be simple (maintenance) or more technical (drainage, sensors, ventilation, refrigerant charge, etc.). Our approach remains the same: a complete diagnosis, a clean repair, and measurable results.
The system in question: Tosot wall-mounted indoor unit (mini-split type)
The photo clearly shows a wall-mounted unit with the hood open and the front filters accessible. This is the most common residential format in Montreal: discreet, efficient, and perfect for condos and multi-story houses.
Regarding the model, without a legible label in the image, we can still identify it as a consistent unit: Tosot (residential wall-mounted range, type “Lomo / equivalent”) . The key point here is not the exact series name, but the components involved: filters, heat exchanger (evaporator), condensate tray, drainage, and fan .
Symptoms observed on site
Upon our arrival, we confirmed several clues that quickly pointed to the diagnosis:
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Reduced airflow (even in high fan mode)
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Uneven comfort : the room takes longer to reach the desired temperature.
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Traces of dust and dirt visible at the filters (with the hood open)
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Slight sign of dampness/odor at startup, typical of a tank or drain that retains water
These symptoms, taken together, often point to a classic combination: a clogged filter + a clogged heat exchanger (or a partially blocked drain) . And when a wall unit is lacking air, it can give the impression of a "gas" problem when the core issue is simply... the air no longer flowing properly.
AirGreen diagnostic: check the air, the drainage, then the performance
Our diagnosis was carried out in three stages, in the most logical order (and the most profitable for the client):
1) Inspection of the filtration and air path
The filters visible in the photo are washable . When they become clogged with fine dust (very common in condos, especially with cooking, pets, renovations, or simply heavy use), the unit:
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breathing less well
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cools/heats less efficiently
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can create abnormal condensation.
2) Control of the heat exchanger and turbine (ventilation)
Even if the filters are cleaned, the evaporator (the heat exchanger behind the filters) and the turbine can sometimes accumulate a film that reduces heat exchange and degrades air quality. This is often where odors originate.
3) Checking condensate drainage
In air conditioning mode, the unit produces water. If the drain becomes partially clogged, the water stagnates in the tray: odor, humidity, sometimes droplets or safety shutdown depending on the model.
After these checks, we were able to confirm that the main cause of the poor performance was a buildup of dirt (airflow) combined with drainage that needed clearing , rather than a major component failure.
Repair and upgrade: cleaning, clearing, and calibration
We carried out a complete, clean, and residential-specific intervention:
Filter cleaning
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Filter removal and washing
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Drying and putting back in place
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Check the frame's position to prevent unfiltered air from entering.
Heat exchanger cleaning and sanitation
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Targeted cleaning of the heat exchanger (evaporator) to restore heat exchange
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Light sanitation (product suitable for residential HVAC) to limit odors and biological load
Clearance of the condensate drain
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Checking the tray
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Clearing the drain (without unnecessarily “forcing” it, to protect the installation)
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Flow test to ensure that the water drains properly
Performance verification after recommissioning
Once the unit was reassembled, we validated:
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significantly improved airflow ,
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operational stability
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Comfort felt within minutes.
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start without lingering odor.
Result: restored comfort and stabilized Tosot heat pump
After the intervention, the client immediately noted:
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a stronger and more constant breath ,
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improved ability to cool the area,
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a “lighter” operation (less sensation than the machine forces),
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a more pleasant air quality.
This is exactly the type of repair/maintenance that extends the life of a Tosot wall-mounted heat pump, while reducing the risk of secondary failures (sensors disturbed by humidity, overloaded ventilation, condensate overflows, etc.).
Here's what we recommend (simple and effective) to prevent it from happening again.
Without adding to the client's routine, our recommendations are clear:
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Clean the filters regularly (frequency varies depending on usage, pets, dust).
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Keep the area uncluttered (curtains, furniture too close together)
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Schedule periodic preventative maintenance if the device is used intensively in summer/winter
At AirGreen, we prefer to be proactive: a well-maintained wall unit means less noise, more efficiency, lower costs , and consistent comfort during real heat (and cold) peaks.