An indoor unit that cooled less effectively and showed signs of drainage failure
In Delson, on the South Shore, we were called for a wall-mounted heat pump repair installed in an open living room, near a large window and above a blind. The client had noticed several worrying signs: a drop in cooling performance, weaker airflow, a slight musty smell at startup, and especially water stains near the area under the indoor unit.
The device was still working. It turned on, responded to the remote control, and blew air. However, comfort was no longer stable. In a home, this type of situation is often more difficult to interpret than a complete breakdown, because the machine gives the impression of working while gradually losing its efficiency. It is precisely in these cases that an accurate HVAC diagnosis becomes essential.
On site, the wall-mounted indoor unit was installed very close to the ceiling, above a window, in a space where air circulation can be influenced by blinds, solar heat, and dust accumulation. The visible status light on the device confirmed that the system was powered, but the behavior reported by the client indicated an internal problem related either to drainage, clogging, sensor reading, or a combination of these factors.
Our intervention therefore began with a complete inspection of the indoor unit, the condensate tray, the filters, the ventilation wheel, the evaporator coil, the drain, and the general operation in cooling mode.
Symptoms observed before the intervention
The client explained to us that the wall-mounted heat pump had started to lose efficiency a few weeks earlier. At first, the problem seemed minor: the room simply took longer to cool down. Then, the blown air became less consistent, with a less distinct feeling of freshness. Finally, unusual humidity appeared around the indoor unit, accompanied by a slight odor when the device started after a period of inactivity.
These symptoms often point the diagnosis towards several possible causes:
- clogged indoor filters;
- clogged evaporator coil;
- ventilation wheel loaded with dust;
- partially blocked condensate tray;
- clogged condensate drain;
- poor drain slope;
- displaced or dirty temperature sensor;
- reduced fan speed due to dirt buildup;
- beginning of frost on the coil due to poor airflow.
In this case, the most important signs were the loss of airflow and moisture near the unit. A heat pump naturally produces condensation in cooling mode, but this water must be properly drained. If the drain is partially blocked, water can accumulate in the pan, create odors, reduce air quality, and eventually leak inside.
A wall heat pump installed in a sensitive area
The location of the indoor unit plays an important role in the aging of a system. In Delson, this wall heat pump was installed above a window with a blind, in a room where the air can contain fine dust from the kitchen, textiles, and daily activity.
A wall unit installed in this type of environment can accumulate dirt more quickly:
Dust on the filters
Filters are the first barrier. When saturated, airflow decreases, the system works harder, and the coil can become too cold.
Deposits on the fan wheel
The fan wheel, also called the turbine or blower wheel, can accumulate a layer of sticky dust. This buildup reduces blowing power and can cause vibrations or irregular noise.
Dirt in the condensate pan
Moisture, dust, and organic particles can build up in the drain pan. Over time, this buildup can partially block the drain.
Odors at startup
A persistent musty smell is not normal. It often indicates that the inside of the unit needs a deeper cleaning.
This installation was therefore not just a wall unit to be quickly cleaned. The entire system needed to be checked: air intake, heat exchange, ventilation, drainage, and condensate removal.
AirGreen Diagnosis: inspection of the indoor unit
We started by removing the filters and inspecting the general condition inside the unit. The filters were dirty, which explained part of the reduced airflow. The evaporator coil also showed a visible accumulation of fine dust in some areas. This type of dirt acts as a barrier between the room air and the cold coil, reducing the air conditioning efficiency.
Next, we inspected the fan wheel. This is often the forgotten element during superficial maintenance. Even when filters are occasionally cleaned, the wheel can accumulate deposits over time. In this case, the ventilation was weakened by internal buildup, which contributed to the feeling of less powerful airflow.
We also checked the condensate tray. The presence of stagnant moisture and deposits indicated that the drain was not working properly. The system was not necessarily completely blocked, but the drainage was slow, which was enough to cause water buildup and an unpleasant odor.
Condensate drain check
The condensate drain is a simple-looking but essential component for the operation of a wall-mounted heat pump. In cooling mode, the warm, humid air in the room passes over the cold coil. The humidity turns into water, falls into the condensate tray, then drains away through the drain.
When the drain is partially blocked, several problems can arise:
- water leakage inside;
- musty smell;
- gurgling noise;
- accumulation in the tray;
- risk of wall damage;
- decreased air quality;
- safety shutdown on some installations equipped with a detector.
In this intervention in Delson, the drain was slowed by a buildup of deposits. We carried out a controlled unclogging, followed by a flow test with clean water to confirm that the drainage was working properly.
Technical cleaning of the indoor unit
After the diagnosis, we performed a complete cleaning of the accessible parts of the indoor unit. This step is very different from a simple filter cleaning. Technical maintenance aims to restore air passage and water drainage while reducing odors and the risk of recurrence.
The intervention included:
- cleaning of the filters;
- cleaning of the evaporator coil with an appropriate method;
- cleaning of the fan wheel;
- cleaning of the condensate tray;
- drain unclogging;
- flow test;
- inspection of the air vents;
- checking the unit's behavior in cooling mode.
We worked carefully around the wall, the blind, and the interior surfaces to protect the living space. An HVAC repair in an occupied room requires as much technical rigor as care in execution.
Sensor and operation check
Once the cleaning was completed, we restarted the device to check its behavior. The airflow was more stable, the blowing temperature more consistent, and the musty smell had noticeably decreased.
We also checked that the louvers opened properly and that the unit responded well to controls. No immediate signs pointed to a faulty electronic board or major motor failure. The main problem was related to internal dirt buildup and slowed drainage.
No major parts were replaced during this service. The system mainly needed technical refurbishment. However, we secured some accessible drain components and recommended monitoring in the following days to confirm that no drops reappeared under the unit.
Comfort restored and prevention of recurrence
After the service, the wall-mounted heat pump returned to healthier operation. The client noticed better air circulation and a quicker feeling of coolness in the room. The drain properly evacuated condensation water, reducing the risk of indoor leakage and persistent odors.
This type of repair is very common in Greater Montreal, especially in Montreal, Laval, Longueuil, on the North Shore and the South Shore, where wall-mounted heat pumps are often used intensively during the summer. When a unit runs for several hours a day during hot periods, humidity and dust eventually build up in the internal areas.
Why a wall unit can leak inside
Water leakage inside is not always caused by poor installation. Even a well-installed unit can develop drainage problems over time. The most common causes are:
A clogged drain
Dust, organic deposits, and humidity can form a partial clog. Water then accumulates in the pan and eventually overflows.
A dirty indoor unit
When the coil and fan wheel are dirty, airflow decreases. The system can produce more condensation under less stable conditions.
Insufficient drain slope
If the drain has shifted or its path is not optimal, water may drain too slowly.
Lack of maintenance
Filters alone do not provide full protection. A wall unit requires more thorough maintenance at regular intervals.
Prolonged use in high humidity
On hot and humid days, the amount of water produced can increase significantly. A drain that is already slow then becomes insufficient.
Mistakes to avoid with a wall-mounted heat pump
This intervention in Delson illustrates several mistakes we often see during service calls.
The first mistake is waiting until water flows abundantly before acting. A small trace of moisture, an odor at startup, or a drain noise are already signals to take seriously.
The second mistake is cleaning only the filters thinking the unit is fully maintained. Filters are important, but the fan wheel, coil, and condensate tray also require professional attention.
The third mistake is using products not suited for the inside of the unit. Some cleaners can leave residues, damage components, or create stronger odors.
The fourth mistake is ignoring drainage quality. A wall-mounted heat pump can cool properly for a while, even with a slowed drain, until water starts to overflow.
The fifth mistake is to quickly conclude there is a refrigerant shortage. A performance drop can come from poor airflow. Adding refrigerant without diagnosis does not fix a clogging or drainage problem.
AirGreen’s tips to extend the system’s lifespan
To prevent this type of problem from recurring, we recommended the customer a few simple and effective actions:
- clean the filters regularly during the cooling season;
- watch for odors when starting up;
- check that no water is leaking under the unit;
- avoid blocking the airflow with blinds, curtains, or furniture;
- schedule professional maintenance when airflow decreases;
- have the drain inspected if the unit often runs during humid periods.
A well-maintained wall-mounted heat pump offers better comfort, consumes less energy, and reduces the risk of breakdown. In a residence in Delson, where temperature and humidity variations can be significant between seasons, this maintenance becomes particularly useful.
A precise approach rather than an unnecessary replacement
In this case, the customer feared the system was at the end of its life. However, the unit still responded well once cleaned and put back in order. The right solution was not to replace the heat pump, but to correct the real causes of the performance drop.
This is an important distinction. A successful wall-mounted heat pump repair is not about randomly changing parts. It involves understanding why the system no longer delivers the expected comfort, then intervening in the right place.
In Delson, the combination of technical cleaning, drain unclogging, and a complete operation check restored the system to more stable performance. The customer was able to resume normal use of their heat pump without fear of immediate internal leakage.
Why choose AirGreen for an HVAC service call
At AirGreen, we work every week on wall, central, multi-zone systems, and other residential equipment throughout Greater Montreal. Our field experience in Montreal, Laval, Longueuil, on the North Shore and the South Shore allows us to quickly recognize typical symptoms as well as less visible details that explain a breakdown.
In this intervention, the image of the indoor unit did not show a dramatic failure. Yet, behind a clean appearance, the device had an airflow and drainage problem that directly affected comfort. This is exactly why professional diagnostics are essential.
We put the machine back into service with a comprehensive approach: inspection, cleaning, unclogging, drainage testing, airflow validation, and clear explanation to the customer. The result was tangible: less humidity, better comfort, a quieter system, and more reassuring use.
Final result: a cleaner, more efficient, and better-drained wall-mounted heat pump
At the end of the service call, the wall-mounted heat pump installed in Delson was operating with improved airflow and restored drainage. The risk of internal leakage had been reduced, the musty smell had decreased, and the customer knew exactly what signs to watch for.
This repair shows that well-executed technical maintenance can make a real difference in the performance of a wall system. Even when the device still turns on, internal buildup can reduce its efficiency, increase humidity, and harm daily comfort.
For AirGreen, every HVAC service call is an opportunity to fix the current problem but also to prevent the next breakdown. In this case, a wall-mounted heat pump that seemed simply "less powerful than before" regained much more reliable operation thanks to precise diagnostics and targeted intervention.