A FUJITSU heat pump losing its heating power as the cold set in in Verdun
In the Verdun neighborhood, our AirGreen team was called for a very specific problem: a FUJITSU wall heat pump, with an outdoor Halcyon DC Inverter unit, was no longer heating as consistently as before. The device was still working, the outdoor fan started, the indoor unit responded to commands, but the comfort inside the house was no longer stable. During cold periods, the client noticed that the indoor temperature gradually dropped even when the setpoint was increased.
The outdoor unit was installed on a wall bracket fixed to a brick facade, in a narrow side yard near a fence. This setup is very common in Montreal, especially in areas like Verdun where outdoor spaces are sometimes limited. The heat pump was well elevated from the ground, an important advantage in winter, but its immediate environment required close inspection: proximity to the brick wall, restricted lateral airflow, exposure to snow, possible vibrations on the wall bracket, and debris accumulation around the base.
The client initially thought the device was simply less efficient due to the outdoor temperature. However, a well-maintained wall heat pump should maintain consistent performance even as the cold increases, according to its capacity and design limits. When the system starts blowing less heat, defrosting too often, or producing irregular cycles, more than just a remote control adjustment needs to be checked.
An outdoor FUJITSU Halcyon DC Inverter unit installed on a wall bracket
On site, we identified an outdoor unit FUJITSU Halcyon DC Inverter, connected to a wall-mounted indoor unit. This is a mini-split wall heat pump configuration, commonly used to heat and cool a main area of a residence, condo, or plex in Montreal.
The exact model was not readable from the front photo, but the unit size corresponds to a typical residential capacity of about 12,000 to 18,000 BTU, depending on the paired indoor unit and the nameplate. These FUJITSU systems are known for their inverter technology, which allows power modulation instead of just on-off operation. This modulation is precisely what provides better comfort, fewer temperature fluctuations, and better energy efficiency when the system is clean, properly charged, and well ventilated.
The wall-mounted installation had several elements to check:
- strength of anchors in the brick;
- level of the outdoor unit;
- rear and side clearance;
- snow or ice accumulation around the condenser;
- condition of the outdoor coil;
- vibration transmitted to the wall;
- condition of refrigerant lines;
- protection of cables and drain;
- outdoor fan behavior;
- defrost sequence.
This step is essential because a wall-mounted heat pump is never diagnosed solely from the inside. A problem felt in the room can come from the outdoor unit, the refrigerant circuit, the airflow, a sensor, an electronic board, a fan, lack of maintenance, or an installation that has become less optimal over time.
Symptoms reported by the customer
During the service call, the customer described a progressive situation. The unit was not completely stopped, but its behavior had changed.
The main symptoms were as follows:
- less powerful heating than before;
- air sometimes blown lukewarm instead of clearly hot;
- more frequent defrost cycles;
- more noticeable outdoor noise during some startups;
- frost buildup on certain areas of the outdoor unit;
- difficulty maintaining the requested temperature;
- feeling that the heat pump was running longer for less result;
- concern about a possible compressor problem.
These symptoms can have several causes. In a FUJITSU inverter system, it is important to distinguish normal modulation behavior from a real performance problem. A heat pump can temporarily reduce its power during defrosting, but it should then resume efficient operation. If defrost cycles become too frequent or if the system does not recover well after each cycle, further diagnosis is needed.
Initial inspection: outdoor environment and air circulation
The first thing we checked was the environment of the outdoor unit. In Verdun, narrow yards, brick walls, and fences can create particular conditions. An outdoor unit needs to breathe. Even if it seems well placed, restricted airflow can reduce its ability to extract heat from the outside air in heating mode.
In this case, the unit was installed on a wall support, which partially protected it from direct snow accumulation on the ground. However, we noticed that air circulation around the unit could be influenced by the proximity of the fence and the wall. This was not necessarily an installation error, but it was a factor to consider in the diagnosis.
We inspected:
The outdoor coil
The coil was partially clogged with dust, fine particles, and external residues. In winter, a dirty coil can freeze faster and reduce heat transfer capacity. The heat pump then has to work harder to extract heat, which can lead to more frequent defrost cycles.
The outdoor fan
The fan had to be checked to confirm it turned freely, without friction, excessive vibration, or obstruction. A fan that slows down or strains can significantly reduce system performance.
The wall support
We checked the support points, level, and stability. A slightly loose support can amplify vibrations and give the impression that a mechanical component is in poor condition, while the noise sometimes comes from the structure.
Defrost water drainage
In heating mode, a heat pump produces water during defrost cycles. If this water accumulates and refreezes under the unit, it can create an ice block that eventually harms the unit. In this case, the wall elevation helped a lot, but we still checked that the water could properly drain away from the base.
HVAC diagnosis: confirm the cause before any repair
After the external inspection, we proceeded with the operational tests. The goal was to evaluate the complete system sequence: heating demand, indoor unit start-up, outdoor unit activation, compressor modulation, blowing temperature, fan behavior, and stability after a few minutes.
Blowing temperature
We measured the temperature of the air blown inside. It was lower than we expected for a system operating normally under these conditions. This result confirmed the customer's perception: the performance drop was real.
Pressure and refrigeration behavior
Measurements helped assess whether the system showed signs of refrigerant shortage or restriction. On an inverter heat pump, interpretation requires experience because the machine constantly modulates. It is not enough to look at a pressure at a single moment: you must observe the trend, the compressor’s response, and consistency with the outdoor temperature.
In this case, we did not find any obvious sign of major compressor failure. The problem seemed more related to a combination of reduced outdoor airflow due to coil fouling, a less effective defrost cycle, and a need to clean the unit.
Sensor verification
Sensors play a crucial role in the operation of a FUJITSU heat pump. An outdoor sensor or coil sensor that misreads temperature can affect defrosting, modulation, and power demand. We validated accessible readings and the consistency of the machine’s behavior.
Electrical inspection
We also checked accessible connections, power supply, and signs of overheating. A weakened or oxidized connection can cause intermittent shutdowns or irregular responses, especially in cold and humid conditions.
Performed intervention: condenser cleaning, correction of sensitive points, and heating tests
Once the diagnosis was made, we proceeded with targeted restoration of the FUJITSU heat pump. The intervention aimed to improve heat transfer, stabilize operation, and reduce inefficient cycles.
Cleaning of the outdoor coil
The outdoor coil was carefully cleaned to remove residues that were limiting airflow. This step is often underestimated. An outdoor condenser may look clean from a distance, but the fins can hold a significant amount of dust, pollen, decomposed leaves, brick particles, urban dirt, and moisture.
In Verdun, as in several neighborhoods of Montreal, outdoor units installed near walls and fences can accumulate fine particles more quickly. A clean coil allows the heat pump to better capture outdoor heat in winter and better reject heat in summer.
Inspection and stabilization of the outdoor fan
We observed the fan over several cycles to confirm its stability. No major mechanical blockage was found, but cleaning around the grille and coil improved overall air circulation. The noise perceived by the customer was amplified by the increased effort of the system and possible resonance from the wall mount.
Defrost control
The defrost cycle was monitored to confirm that the unit could properly free itself from frost. A heat pump in winter must periodically reverse its cycle to defrost the outdoor unit. This process is normal. What is not normal is defrosting that is too frequent, incomplete, or followed by too weak a heating recovery.
After cleaning and verification, the behavior was more consistent: the unit better resumed heat production after defrost cycles.
Inspection of refrigerant lines and insulation
We checked the visible condition of the lines. Damaged insulation on the refrigerant line can cause losses, especially when the line is exposed to temperature variations. Accessible sections were inspected to confirm that no obvious degradation contributed to the problem.
Final tests in heating mode
After the intervention, we restarted the system and conducted extended tests. The discharge temperature improved, cycles were more stable, and the outdoor unit operated with less apparent effort. The customer noticed that the blown air was warmer and that the heat pump responded better to the setpoint.
The results obtained:
- better discharge temperature;
- more stable outdoor ventilation;
- reduced noise related to system effort;
- more consistent defrosting;
- better maintenance of indoor temperature;
- no immediate indication of compressor failure;
- device restored to more reliable operating condition.
Why a FUJITSU heat pump can lose performance in winter
A wall-mounted inverter heat pump is an efficient system but sensitive to operating conditions. Several factors can reduce its performance without the device being completely faulty.
Dirty outdoor coil
Even a thin layer of dirt reduces heat exchange. In heating mode, the outdoor unit must absorb heat from the cold air. If the coil is dirty, the machine loses efficiency.
Snow or ice buildup
Snow around the unit can reduce air circulation. Ice can also interfere with defrost drainage. A wall-mounted installation helps but does not replace regular inspection.
Insufficient clearance
A condenser near a wall, fence, or obstacle can recycle some of its own air. This affects performance, especially when heating demand is high.
Inaccurate or poorly influenced sensors
Incorrect temperature readings can alter the defrost logic or compressor modulation.
Irregular maintenance
A system that is not maintained for several seasons can gradually lose capacity without a dramatic failure. The client often notices the problem only during a cold snap.
Mistakes to avoid with a wall-mounted heat pump in winter
We also advised the client on some best practices to prevent the problem from recurring.
These should be avoided:
- to let snow accumulate around the outdoor unit;
- to completely cover the condenser with a cover during use;
- to close the shutters or block the indoor unit;
- to constantly set the temperature to maximum;
- to ignore too frequent defrost cycles;
- to scrape the coil with a hard object;
- to pour hot water on a frozen unit without diagnosis;
- to postpone maintenance when airflow decreases.
A well-maintained FUJITSU heat pump can provide excellent comfort, but it must be inspected when its behavior changes.
A representative intervention of AirGreen service calls in Verdun
This repair in Verdun demonstrates the importance of a complete diagnosis. The client feared a major breakdown, possibly a compressor replacement. After inspection, the situation was more nuanced: the machine needed technical refurbishment, exterior cleaning, defrosting verification, and a full validation of its operation.
At AirGreen, we regularly work on similar systems in Montreal, Laval, Longueuil, on the North Shore and the South Shore. FUJITSU, GREE, SHARP, MIDEA, LG, DAIKIN wall-mounted heat pumps and other brands all require a rigorous approach: understanding the symptoms, measuring parameters, inspecting components, and repairing only what needs to be fixed.
In this case, the FUJITSU wall-mounted heat pump was able to regain more stable performance without a complete replacement. The client received a clear response, measurable improvement, and practical advice to keep the device in good condition for the rest of the cold season.