Water leakage under the indoor unit revealing a drainage and airflow problem
In LaSalle, our AirGreen team was called for a wall heat pump repair installed high in a residential bedroom, directly above a storage space and near a patio door. The indoor unit, visible in the photo, was running with a display at 22 °C, but the client noticed abnormal behavior: small traces of moisture appeared under the device, the airflow seemed less powerful than before, and the room took longer to reach the requested temperature.
The machine was a wall-mounted mini-split heat pump, with a typical residential capacity of about 12,000 BTU, mainly used to cool and temper a closed room. The exact brand was not clearly identifiable on the front from the image, but the configuration matched a standard compact wall unit, with horizontal directional louvers, front display, and side access to technical information.
This type of problem is common in homes in Montreal, especially when the unit is installed near the ceiling, in a room where air circulation is influenced by tall furniture, moldings, windows, and doors. In this particular case, the issue was not just to make the visible water disappear: it was necessary to understand why the heat pump was no longer properly managing its condensate.
Symptoms observed before our intervention
The client reported several important clues to us:
- presence of moisture under the wall unit;
- less uniform airflow at the outlet;
- feeling that the room was cooling more slowly;
- prolonged operation without quickly reaching the desired comfort;
- ventilation noise slightly duller than before;
- no error code displayed on the front panel.
These symptoms already pointed our diagnosis towards three possible causes: partially clogged condensate drain, dirty indoor turbine, or dust-laden evaporator, reducing heat exchange and increasing moisture production in the internal tray.
A high installation that required a thorough inspection
Since the unit was installed above a storage space, our technician first secured the area under the device. This detail matters a lot: when a wall-mounted heat pump leaks above clothes, woodwork, or a closet, even a small leak can cause visible damage or create a musty smell in the room.
We then proceeded with a complete inspection:
- opening the front panel;
- removal and inspection of filters;
- evaporator inspection;
- checking the condensate tray;
- drain inspection;
- observing the movement of the louvers;
- ventilation test at different speeds;
- reading the blowing temperature;
- checking the stability of the device in cooling mode.
The first observation was clear: the heat pump was working, but its performance was weakened by insufficient maintenance and slowed drainage.
Diagnosis: a slowed drain and a fan loaded with fine dust
After partially removing the panel, we observed that the filters were dirty and the fan had a buildup of fine dust. This kind of buildup does not always prevent the device from starting, but it gradually reduces airflow. The unit then continues to operate, but it becomes less efficient, noisier, and more likely to produce excessive condensation.
Why poor airflow can cause water under the unit
A wall-mounted heat pump naturally produces condensate in cooling mode. The humidity in the air condenses on the evaporator, then the water must flow into the tray and exit through the drain. If the airflow is too low or if the evaporator becomes too cold in certain spots, condensation can become more abundant or unevenly distributed in the tray.
When the drain is also partially blocked, water drains too slowly. It can then accumulate, overflow, or create visible drops under the indoor panel.
In this case in LaSalle, the leak was not massive, but the signs were clear enough to intervene before the problem turned into water damage.
AirGreen intervention: cleaning, unblocking, and performance testing
Our intervention was carried out in several steps, without unnecessary replacement of parts. The goal was to restore the normal operation of the device by correcting the real cause of the problem.
Technical cleaning of the indoor unit
We cleaned the filters, accessible areas of the evaporator, the louvers, and the air outlet. The fan was also cleaned to restore more regular air circulation. This step is essential on a wall heat pump, as a dirty fan can give the impression that the device lacks power even though the outdoor compressor is still working properly.
After cleaning, the airflow was more stable across the entire width of the unit.
Unblocking the condensate drain
We then checked the drain. Flow was present but slowed. The duct was cleaned and tested until smooth drainage was achieved. This step confirmed that the water produced by the evaporator could again exit normally without accumulating in the inner tray.
No condensate pump was replaced, as the installation showed no mechanical failure on that side. The problem was rather due to progressive clogging.
Level and flow check
A slightly tilted wall unit in the wrong direction can also cause a leak. We therefore checked the device’s seating and drainage slope. In this intervention, the unit was acceptably installed, but the slowed drain was enough to explain the observed humidity.
Tests after repair
Once the device was reassembled, we performed the following tests:
- Operation in cooling mode;
- Low, medium, and high ventilation;
- Observation of the condensate tray;
- Flow test;
- Controlling the blowing temperature;
- Checking the louvers;
- Observation of the unit over a full cycle.
The result was positive: the wall heat pump blew more evenly, water drained properly, and no leakage was visible under the unit after the test.
A targeted HVAC repair that prevents water damage and extends the device's lifespan
This intervention demonstrates the importance of an accurate diagnosis. A water leak under a wall heat pump may seem minor, but it should never be ignored. In a room like this, with a unit placed above storage and near exterior openings, humidity can quickly affect woodwork, clothing, walls, or moldings.
Mistakes to avoid with a leaking wall heat pump
Several reactions can worsen the problem:
Raising the temperature without addressing the cause
Simply changing the temperature setting can temporarily reduce condensation, but the drain remains clogged and the problem returns as soon as the device works more intensively.
Using the device despite visible water
A leaking heat pump should be inspected quickly. Water can reach sensitive components, damage the wall, or create an accumulation in the tray.
Clean only the filters
Filters are important, but they do not always solve the problem. The fan, evaporator, and drain must also be checked.
Wait for an error code
In many drainage cases, no error code appears. The unit can continue to operate while causing a leak.
Practical advice given to the client
At the end of the service call, we explained to the client how to reduce the risk of recurrence:
- clean the filters regularly during the hot season;
- watch for any musty odors;
- do not block the air outlet with tall furniture or objects;
- avoid running the unit for long periods if water appears;
- schedule maintenance when airflow becomes weaker;
- have the drain checked before periods of high humidity.
These tips are especially useful in Montreal, where summer humidity puts wall-mounted heat pumps to the test. The same type of problem can also occur in Laval, Longueuil, on the North Shore and the South Shore, especially in residential installations used daily for several months.
Final result: comfort restored and client reassured
After the intervention, the wall-mounted heat pump in this LaSalle home returned to normal operation. Airflow was improved, drainage was restored, and the client could use the unit without fear of leakage under the indoor unit.
No expensive parts were replaced because the diagnosis identified a cause related to clogging and drainage rather than an electronic failure or compressor problem. This is exactly the advantage of professional HVAC service: intervene in the right place, fix the real problem, and avoid unnecessary expenses.
At AirGreen, we regularly repair wall-mounted heat pumps in residential neighborhoods of Montreal, including LaSalle, as well as in Laval, Longueuil, on the North Shore and the South Shore. Each service call is handled with the same approach: observation, diagnosis, clean intervention, thorough testing, and clear explanations to the client.