Repair of a wall-mounted heat pump in Sainte-Thérèse

A wall-mounted heat pump weakened by renovation dust, the age of the device, and compromised airflow

During this service call for a wall-mounted heat pump in Sainte-Thérèse, our AirGreen team intervened in a residence undergoing interior renovation. Upon arrival, the context already explained part of the problem: open walls, door frames under work, protected floors, construction dust in the air, and a wall unit installed high up, close to the ceiling. In this type of environment, a wall-mounted heat pump can quickly lose efficiency, even if it was working properly before.

The visible device was a residential wall-mounted heat pump, of an older generation, with a yellowed casing from age and a front panel showing signs of use. The exact brand and model were not readable from the available visual inspection, but the unit’s format, wall position, and front grille clearly confirmed a mini-split type installation. The exact BTU capacity was not visibly displayed, but this type of unit generally corresponds to a common residential range, often around 9,000 to 12,000 BTU, depending on the room served and the home’s configuration.

The customer contacted us because the heat pump was no longer performing the same. The air seemed less powerful, comfort was inconsistent, and a dust smell was noticeable at startup. In a house under renovation, these symptoms should never be taken lightly: gypsum dust, wood particles, paint residues, fibers, and fine debris can enter the indoor unit, stick to the heat exchanger, accumulate on the ventilation fan, and clog the filters.

Symptoms observed before the intervention

Even before opening the device, several signs pointed our diagnosis towards an airflow problem and internal clogging. The customer had noticed:

• Lower airflow than usual.
• A feeling that the heat pump was running but not distributing air well.
• A dusty smell at startup.
• Uneven performance in the room.
• A slightly different noise when the ventilation increased.
• A concern related to ongoing renovation, especially because of the dust present in the house.

In such a context, it would have been too quick to conclude a compressor failure or refrigerant shortage. A wall-mounted heat pump can lose a lot of efficiency simply because its indoor unit is clogged. The turbine may spin, the flap may open, and the device may seem to operate normally, but air no longer passes properly through the heat exchanger.

Inspection of the indoor unit: an aging machine in a demanding environment

The wall unit was installed very high, near the ceiling, which is common for wall-mounted heat pumps. However, this position requires rigorous maintenance because warm, light dust naturally rises in the room. During renovations, fine particles remain suspended for a long time and eventually get sucked into the device.

The unit’s front panel showed yellowing, a sign of equipment with several years of service. This is not necessarily a problem in itself: many older devices can continue to operate efficiently when well maintained. However, on an older wall-mounted heat pump, some components become more sensitive:

The filters

Filters are the first barrier against dust. When saturated, airflow decreases, heat exchange diminishes, and the device has to work longer to reach the desired temperature.

The indoor evaporator

The indoor heat exchanger can accumulate a compact layer of dust. This layer acts as an insulator and reduces heat transfer capacity. In air conditioning, this can even promote the formation of stagnant moisture and odors.

The ventilation turbine

The turbine is often the most neglected part. It can accumulate a black or gray film made up of dust, moisture, and fine particles. When the turbine blades are clogged, the air output is weaker, even if the motor is running.

The condensate drain

In cooling mode, the indoor unit produces condensation water. If the drain is partially blocked by dust or debris, water may drain poorly, create odors, or cause leaks.

HVAC diagnosis: understanding whether the problem comes from the air, control, or refrigeration circuit

Our diagnosis was carried out in several stages to determine whether the performance drop came from the indoor unit, the refrigeration system, or a control problem.

Startup operation check

We first observed the unit’s behavior at startup. The air flap, indoor fan, and control response were checked. On an older wall unit, a slow-responding flap, a worn fan motor, or an unstable electronic board can create symptoms similar to performance loss.

Airflow control

Airflow was evaluated at different ventilation speeds. The difference between low, medium, and high modes often provides good indications. If the fan speeds up but the airflow remains low, clogging of the turbine or exchanger becomes a very likely cause.

Filter and heat exchanger inspection

The filters were removed and inspected. In a renovation environment, it is common to see filters covered with dust finer than usual household dust. This dust compacts and can significantly reduce airflow.

The indoor heat exchanger was also examined to check for deposits. A dirty exchanger harms both cooling and heating because the heat pump must transfer energy between the room air and the refrigerant.

Drain inspection

We paid special attention to the condensate drain. A wall-mounted heat pump installed in a house under renovation can absorb fine particles that end up in the drainage tray. If the water does not drain properly, the customer may eventually notice an indoor leak, especially in cooling mode.

Thermal response validation

After the initial checks, we assessed the temperature difference between the return air and the supply air. This measurement helps distinguish a machine that does not produce enough cooling or heating from one that produces correctly but does not distribute the air well.

Technical cleaning, targeted checks, and safe recommissioning

The intervention focused on restoring the indoor unit, with particular attention to cleaning, air circulation, and preventing future problems. In the areas of Sainte-Thérèse, Blainville, Boisbriand, as well as in Montreal, Laval, Longueuil, on the North Shore and the South Shore, we often see wall-mounted heat pumps affected by renovations. The problem is not always obvious at first, but it can worsen quickly if the device continues to draw in dust for several weeks.

Filter cleaning and internal inspection

The filters were cleaned and put back in place after inspection. This step is simple but not always sufficient. When a wall-mounted heat pump has operated in a dusty environment, particles often bypass the filters and accumulate further inside the device.

We therefore inspected the inside of the unit to identify the most affected areas. Special attention was given to the turbine, the heat exchanger, and the condensate tray.

Cleaning of the ventilation turbine

The ventilation turbine plays a crucial role in comfort. Even a thin layer of dust on its blades can reduce the volume of air moved. When the turbine is dirty, the customer may feel that the heat pump "blows less," even if the compressor is working.

Targeted cleaning improved air circulation and reduced odors associated with dust buildup. This type of work must be done carefully to avoid unbalancing the turbine or damaging internal components.

Inspection of the condensate tray and drain

The condensate tray was inspected to ensure that no accumulation could block the drainage. In a house under renovation, this point is important: an indoor water leak can damage walls, freshly renovated floors, and ongoing finishes.

We confirmed that the drainage was functional and that the device could be used without immediate risk of overflow.

Functionality test after intervention

Once cleaning and checks were completed, we restarted the heat pump to evaluate its behavior. The airflow was more consistent, the dust odor reduced, and the unit's response more coherent. The client was able to see that the machine did not necessarily need immediate replacement but required maintenance suited to its age and the renovation context.

Recommendations given to the client

In this type of situation, the repair is not limited to the day's intervention. It is also necessary to prevent the problem from recurring during the rest of the renovations. We therefore recommended several practical measures:

Avoid using the unit during dusty work

When sanding, drywall cutting, plastering, or painting is underway, it is best not to operate the wall-mounted heat pump. The unit risks sucking in fine particles that will lodge in the exchanger and turbine.

Clean filters more often during renovation

Normally, filters should be cleaned regularly depending on use. During work, the frequency should be increased. A clean filter protects the unit and maintains better airflow.

Plan a complete cleaning after the work is finished

Even if the unit works better after our intervention, a complete cleaning after renovation is still recommended. Once the work is finished, residual dust can be removed and the indoor unit can start fresh and healthier.

Monitor signs of leaks or odors

A persistent odor, abnormal noise, or water trace under the unit must be addressed quickly. The sooner the intervention, the easier it is to avoid damage to walls or finishes.

Why this type of service call requires experience

An old wall-mounted heat pump installed in a renovated house can show several contradictory symptoms. The client may believe the unit is low on refrigerant, that the outdoor compressor is faulty, or that the machine is simply too old. However, in many cases, the problem initially comes from the indoor unit: dust, reduced airflow, clogged turbine, saturated filter, or partially blocked drain.

Field experience prevents unnecessary replacement of costly parts. Before recommending a major repair, we check the fundamental elements: air, cleanliness, drainage, control, thermal response, and general condition. This method protects the client from incomplete diagnoses and helps extend the equipment's lifespan when reasonable.

Mistakes to avoid with a wall-mounted heat pump during renovations

Many homeowners run their heat pump during renovations to keep the house comfortable. This is understandable but risky. A wall unit is not designed to filter construction dust. The most common mistakes are:

• Leaving the unit running during wall sanding.
• Not cleaning the filters for several weeks.
• Partially covering the unit without completely shutting it down.
• Ignoring a dust smell at startup.
• Waiting for a water leak to appear before inspecting the drain.
• Assuming that low airflow automatically means the machine is at the end of its life.

A wall-mounted heat pump can be robust, but it remains sensitive to the quality of the air it draws in. In a home under renovation, it must be protected like a precision mechanical device.

Restored comfort and a better strategy for the continuation of the work

At the end of the service call in Sainte-Thérèse, the client had a much clearer understanding of the condition of their system. The unit was not perfect, mainly due to its age, but it could continue to provide comfort with proper maintenance. The intervention restored better airflow, reduced dust-related odors, and ensured safe use during the renovation period.

For AirGreen, this type of intervention perfectly sums up our approach to residential HVAC repair: observe the real context, diagnose methodically, intervene precisely, and provide the client with useful recommendations. Whether in Sainte-Thérèse, Montreal, Laval, Longueuil, on the North Shore or the South Shore, a wall-mounted heat pump deserves a thorough analysis before any replacement decision.

An older machine can still be useful when well maintained. But in a renovation environment, it must be closely monitored. Thanks to this intervention, the client was able to continue their work with a cleaner, more stable system that is less likely to cause comfort or drainage issues.