In a condo in Ville-Marie , our AirGreen technicians were called to service a Tosot wall-mounted heat pump (an indoor unit installed high up, near a corner, typical of urban spaces where every centimeter counts). At first glance, everything seemed normal: the unit was securely fastened, the air vent was working, and the installation appeared clean. Yet, the comfort was gone—and this is exactly the kind of situation where a thorough diagnosis makes all the difference.
In this article, we show you how we proceed , step by step, to restore a Tosot wall-mounted heat pump (here, a consistent model from the Tosot Lomo range, very common in residential use) to its optimal performance, without approximations.
Context: symptoms reported by the client
The client contacted us about three specific problems:
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Uneven cooling : the room reached the required temperature, then quickly lost it.
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Reduced airflow : the blowing was weaker, even at high power.
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Uncomfortable humidity : feeling of “heavy” air, particularly in the evening.
In a condo, these symptoms are often amplified: more compact spaces, accumulated heat, and air circulation more sensitive to the slightest restriction (filtration, dirty exchanger, partially obstructed drainage, etc.).
Type of machine and installation observed
This is a Tosot brand wall-mounted heat pump (mini-split / wall unit) , installed:
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Very high on the wall , near the ceiling (good for diffusion, but demanding for maintenance);
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Being close to a corner can slightly influence air circulation if the shutters are not properly oriented;
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In a clean residential environment, with access by stepladder , which indicates a maintainable unit but requiring a safe working method (protection, wash basin, flow control).
Even when the installation is done correctly, a wall-mounted heat pump remains a system that breathes : if the air does not circulate properly, the performance collapses.
AirGreen diagnostic: what we check (and why)
Our approach is to never guess . A Tosot that “no longer cools like it used to” may have a simple cause… or the beginning of a problem that, if ignored, ends in a costly breakdown.
1) Checking the airflow and filters
We always start with the essentials:
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Condition of the filters (fine dust, cooking grease, lint);
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Cleanliness of the air intake area;
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Position and mobility of the shutters (horizontal and vertical).
An overly clogged filter can reduce flow, cause inefficient heat exchange, and even promote frost on the evaporator.
2) Inspection of the heat exchanger (evaporator) and the turbine
Next, we look at what the customer doesn't see:
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Condition of the evaporator fins (dust stuck = thermal insulation);
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Turbine (fan wheel) fouling: very common in condos, especially if the unit often runs at low speed.
A clogged turbine can create:
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noise,
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a reduced airflow,
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an unequal distribution,
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and a persistent feeling of humidity (dehumidification depends directly on good heat exchange).
3) Condensate drainage control
When a customer mentions discomfort + humidity, we systematically check:
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Recycling bin;
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Drain slope;
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Beginning of obstruction (biofilm);
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Micro-leaks or seepage.
Even a partial blockage can prevent proper drainage, create internal moisture and, eventually, odors or leaks.
4) Electrical controls and sensors
On a Tosot, we pay attention to:
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Connections and power supply;
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Temperature sensors (ambient and coil);
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Signs of intermittent errors (sometimes not displayed if the system “recovers” from the situation).
5) Refrigeration checks (if necessary)
If the previous steps are not sufficient to explain the performance drop, we proceed to more in-depth checks:
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Supply and return air temperatures;
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Behavior in air conditioning mode;
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Undercharge indices (without “inventing” an addition of refrigerant: we confirm first).
Problem identified: fouling + partially blocked drainage
In this case, the cause was twofold (and very typical in residential settings):
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Accumulation of fine dust on the evaporator and turbine , reducing the flow rate and efficiency of heat exchange.
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The condensate drain was partially blocked , which hampered dehumidification and created a feeling of more humid air than it should be.
The result: the Tosot heat pump was working, but it was working harder to produce less heat . And that's exactly the scenario that increases the electricity bill while reducing comfort.
Repair/intervention: what we did on site
1) Safety and environmental protection
First and foremost:
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Protection of the wall, floor and furniture;
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Installation of a suitable washing basin;
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Stabilizing access (working at height).
2) Complete cleaning of the indoor unit
We proceeded to:
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Cleaning of filters (if recoverable) and checking their condition;
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Thorough cleaning of the evaporator (fins);
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Turbine cleaning to restore normal airflow;
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Targeted light disinfection (as needed) to limit odors and biofilm.
This cleaning is not "cosmetic". On a wall-mounted heat pump, it is often what restores the original performance .
3) Restoration of the drainage system
We have :
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Unblocked the drain and eliminated the beginning of biofilm;
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Validated continuous flow;
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Checked for absence of seepage at the outlet of the tank.
4) Functional tests and calibration during use
After reassembly, we have:
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Measured the stability of the blowing;
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Confirmed that the temperature remains stable without fluctuations;
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Adjusted the orientation of the louvers for more even diffusion (useful in a room where the unit is close to a corner);
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Advised the customer on simple settings to maximize comfort and savings (mode, auto speed, realistic setting).
Results: restored comfort, more stable operation
Once the procedure was complete, the difference was immediate:
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More powerful and consistent airflow
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More consistent cooling
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drier and more comfortable air
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Less ventilation noise
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General feeling: the Tosot heat pump is “back up to speed”
That is exactly what we are aiming for: not just “repairing”, but bringing performance back to the expected level .
Our AirGreen tip: simple prevention, breakdowns avoided
For a Tosot wall-mounted heat pump, especially in a condo in Ville-Marie, here is what we recommend:
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Clean the filters regularly (more often if open kitchen, pets, urban dust);
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Plan for complete periodic maintenance (evaporator + turbine + drainage), not just a “quick rinse”;
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Don't wait for a breakdown: a drop in flow rate or efficiency is often a sign of fouling.
A well-maintained wall-mounted heat pump offers:
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improved comfort
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less mechanical stress,
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improved energy efficiency
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and an extended lifespan.
Need a Tosot repair in Montreal, Laval or on the South Shore / North Shore?
At AirGreen, we service Tosot wall-mounted heat pumps (and other brands) using a clear method: diagnosis → targeted action → testing → measurable result . Whether it's a drop in performance, a humidity problem, a water leak, an intermittent error, or a system that "works but not as well," we know where to look—and, most importantly, what to fix.