A wall-mounted heat pump in heating mode that no longer kept up during cold days
In Anjou, in the east of Montreal, our AirGreen team was called for a service call on a wall-mounted heat pump installed in a main room directly facing a large window. The customer reported a particularly uncomfortable problem in winter: the indoor unit was running, the light was on, the flap opened partially, but the air blown was not warm enough and the system seemed to enter short cycles too often. The room remained cool despite a constant heating demand.
The photo of this intervention shows a wall-mounted heat pump installed above a window, near a curtain, in a room exposed to the outside cold. Through the window, snow on the ground confirms a winter context, which immediately directs the diagnosis toward a loss of heating performance, a possible defrosting problem, a faulty sensor reading, reduced indoor airflow, or abnormal interaction between the wall unit and the outdoor condenser.
This type of situation is common in Montreal, Laval, Longueuil, on the North Shore and the South Shore, especially when wall-mounted heat pumps operate during extended cold periods. A machine can still start without delivering its full capacity. This often makes the problem hard for the customer to understand: the device is not completely off, but comfort is no longer stable.
In this case in Anjou, the goal of our intervention was clear: to determine whether the heating loss was due to a maintenance issue, lack of air circulation, a faulty sensor, a refrigerant problem, an electronic board issue, or abnormal behavior of the outdoor unit.
Symptoms observed before our arrival
The customer had noticed several specific signs:
- The air blown was lukewarm rather than truly hot;
- The indoor fan seemed less powerful than before;
- The system sometimes stopped before actually heating the room;
- A light remained on on the right side of the unit;
- The lower flap did not always seem to direct the air properly;
- The area near the window remained cold;
- The heating became irregular when the outside temperature dropped.
These symptoms do not automatically point to a major failure. A wall-mounted heat pump that heats poorly may simply be dirty, poorly adjusted, or disturbed by its immediate environment. In this room, the location near a window and a curtain required special attention, as the cold air descending from the window can influence comfort perception, while a curtain too close to the unit can harm the distribution of warm air.
Indoor unit inspection
Our technician first inspected the wall unit without rushing to the outdoor condenser. A good HVAC repair always starts with a complete reading of the indoor system, especially in heating mode.
Airflow inspection
The airflow was lower than expected for a wall unit of this size, estimated around 12,000 BTU according to the device size and the room served. The filters were loaded with fine dust, and the evaporator showed partial buildup between the fins.
In heating mode, reduced airflow can cause several effects: the unit seems to heat less, the internal temperature becomes unstable, the sensor may receive a false reading, and the fan does not distribute heat properly in the room. The client then feels discomfort even if the outdoor compressor is working.
Curtain and air circulation
The unit’s location, very close to the curtain, was also analyzed. The curtain did not completely block the device, but its proximity could disrupt the air outlet when the flap directed the airflow downward. In a room with a large window in winter, it is essential that warm air is projected far enough to compensate for the cold area near the glazing.
We explained to the client that a wall-mounted heat pump can be technically functional but less efficient if the warm air falls immediately near an obstacle or if the natural circulation of the room is interrupted.
Turbine condition
The indoor turbine was dirty. This buildup was not visible from a distance, but it explained much of the low airflow. When a turbine accumulates dust and deposits, it loses its ability to push air. It can also create a faint noise, slight vibration, or uneven heat distribution.
Motorized flap inspection
The lower flap still responded to commands, but its movement was less smooth than expected. No immediate replacement of the flap motor was necessary. Dirt buildup around the air outlet and mechanical aging mainly contributed to less effective airflow direction.
Electronic and thermal diagnostics
After the mechanical inspection, our technician continued with operational checks.
We checked:
- remote control response;
- heating and ventilation modes;
- return air temperature;
- blown air temperature;
- temperature variation after a few minutes of operation;
- response of the indoor temperature sensor;
- fan speed;
- damper behavior;
- cycle stability;
- communication with the outdoor unit.
The system was receiving commands properly and showed no blocking error codes at the time of inspection. However, the measured performance confirmed a loss of efficiency mainly related to indoor air exchange, with a possibility of an outdoor cycle to monitor depending on cold conditions.
Inspection of heating operation
In heating mode, a wall-mounted heat pump does not operate exactly like a traditional electric heater. It extracts heat from the outside air and transfers it inside. When it’s cold, the outdoor unit may enter defrost mode, which is normal. But if the indoor unit is dirty or the airflow is too low, comfort becomes uneven and the customer may believe the system is no longer heating.
In this case in Anjou, the problem was not a total lack of heating. The machine produced heat, but it did not distribute it properly and did not maintain the room at the expected level. This distinction is important because it helps avoid premature equipment replacement.
Internal cleaning, adjustments, and system performance restoration
The intervention was focused on a complete performance restoration of the indoor unit, accompanied by targeted checks to confirm that the wall-mounted heat pump could continue to heat properly.
Cleaning of filters and evaporator
The filters were removed, cleaned, and inspected. Then, the evaporator was treated with an appropriate method to free the fins without damaging them. Even a slight buildup on the coil can reduce heat exchange, especially when the machine runs for long periods in winter.
After this step, air flowed more easily through the unit. The system could better transfer heat and stabilize its blowing temperature.
Cleaning of the fan turbine
The turbine was one of the key points of the repair. We performed a thorough cleaning of the fan wheel to remove deposits that were limiting the airflow. This work requires patience, as a poorly cleaned turbine can retain unbalanced areas and still produce noise.
Once the fan was restored, the airflow became more uniform. The room received more warm air, which improved the comfort feeling near the window.
Correcting the airflow direction
We adjusted the flap orientation and advised more efficient use of the heating mode. In winter, it is often better to direct warm air downward and toward the center of the room rather than letting it flow immediately along the ceiling. Since warm air naturally rises, poor orientation can create a temperature difference between the top of the room and the occupied area.
We also recommended keeping the curtain sufficiently clear of the unit when the heat pump is running. This simple detail can improve heat distribution and prevent a false impression of a breakdown.
Checking the drain and internal humidity
Even in winter, the condensate drain deserves checking. Some units can accumulate moisture, dust, or residue, especially after several cooling seasons. The drain was not completely blocked, but the inspection confirmed that no internal leaks were present at the time of the call.
Test after restart
After cleaning and adjustments, we put the wall-mounted heat pump back into operation. The result was clearly noticeable:
- the airflow was stronger;
- the blown air was more consistent;
- the room responded better to heating demand;
- the flap operated more freely;
- the system cycled more regularly;
- the ventilation noise was cleaner;
- the client regained more stable comfort in the room.
The heat pump was not new, but it still had useful capacity. The problem mainly came from gradual dirt buildup and imperfect air distribution, worsened by its location near a large window.
Why this diagnosis was important
Without a thorough inspection, this type of problem can be misinterpreted. Many owners immediately think of a refrigerant leak or a faulty compressor when their wall-mounted heat pump heats less effectively. However, in many service calls, the problem actually originates from the indoor unit.
A dirty evaporator, a clogged fan, a saturated filter, or a misaligned flap can significantly reduce comfort without triggering an error code. This is exactly what makes technical intervention essential: you need to measure, observe, clean, and test before drawing conclusions.
Mistakes to avoid with a wall-mounted heat pump in winter
Turning the temperature too high
Setting the remote control to a very high temperature does not fix an airflow problem. The heat pump will work longer, but heat will not be better distributed if the indoor unit is dirty.
Letting filters accumulate
Filters must be cleaned regularly. However, even clean filters do not guarantee that the turbine and evaporator are clean. Internal maintenance remains necessary after several seasons.
Blocking air with a curtain or furniture
An obstacle near the unit can reduce heating efficiency. In a room like this, with a large window, airflow must remain free to counteract the cold wall effect.
Confusing normal defrosting with a breakdown
In winter, a heat pump may temporarily stop blowing warm air during a defrost cycle. This behavior can be normal. What is not normal is a constant loss of performance, low airflow, or a room that never heats properly.
Postponing maintenance until failure
A wall-mounted heat pump that runs every day should be inspected before comfort becomes insufficient. Preventive maintenance can avoid more costly repairs.
An AirGreen intervention adapted to Anjou’s realities
This service in Anjou demonstrates the importance of a precise approach to wall-mounted heat pump repair. The unit was installed in a room exposed to outdoor cold, above a window, with airflow sensitive to the curtain’s position. The diagnosis had to consider both the internal mechanics and the room’s environment.
At AirGreen, we service residential HVAC systems throughout Greater Montreal, including Montreal, Laval, Longueuil, the North Shore, and the South Shore. Our service calls cover issues such as insufficient heating, noise, water leaks, loss of air conditioning, error codes, electrical failures, advanced maintenance, internal cleaning, and full diagnostics.
In this specific case, the solution was not to unnecessarily replace the equipment, but to restore its operation: cleaning the evaporator, cleaning the turbine, correcting the airflow, checking the damper, inspecting the drain, and performing heating performance tests. The client regained a more comfortable room, a quieter device, and greater confidence in their system.