Little-known traps that compromise performance, durability, and comfort—and that top installers know how to sidestep
Installing a wall-mounted air conditioner or a wall-mounted heat pump in Longueuil may seem simple at first glance. Yet behind every successful project lies a series of precise technical choices and critical details that make all the difference between a high-performing HVAC system… and a source of costly frustration. At AirGreen, we’ve corrected dozens of incomplete, poorly calibrated, or downright non-compliant installations done by contractors with no HVAC specialization.
In this article, we share the most common mistakes, the ones our experts consistently avoid, and which can seriously affect the performance, lifespan, and energy efficiency of an air conditioning system in Longueuil, as well as throughout the South Shore, Montréal, Laval, and the North Shore.
Mistake #1: Underestimating or overestimating the thermal needs of the home
One of the most frequent mistakes remains incorrect sizing of the wall-mounted air conditioner. Choosing a model that’s too powerful for the space causes short cycling, accelerated wear, and unnecessary electricity consumption. On the other hand, an undersized unit will never deliver stable thermal comfort, especially during heatwaves.
At AirGreen, we always conduct a complete thermal analysis based on:
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Window orientation
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Wall insulation
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Room volume
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Usage type (residential, commercial, rental)
A client in a 4½ condo in Longueuil had a 9,000 BTU unit installed by another contractor. The result: constant overheating in the living room and overworked compressor. We recommended and installed a 12,000 BTU Fujitsu KZAH R32 model, perfectly suited to the layout, with noticeably better performance the very next day.
Mistake #2: Poor placement of the indoor unit
The efficiency of a wall-mounted air conditioner depends heavily on where it’s installed. Too often, units are mounted:
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Too high, near the ceiling
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Too close to a side wall or piece of furniture
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Opposite heat sources (sun-exposed windows, kitchen)
These errors lead to uneven air distribution and dead zones where the temperature remains uncomfortable.
Our teams always choose a central, unobstructed, elevated but accessible location, to maximize airflow circulation. In a duplex in Saint-Hubert, we repositioned a poorly installed Gree unit that was located above a thermal curtain—performance immediately doubled.
Mistake #3: Overlooking the importance of the drainage line
Poor drainage can cause water leaks, mold inside walls, and in some cases, structural damage. Too often, condensate pipes are:
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Improperly sloped
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Poorly insulated
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Missing a lift pump despite vertical drain runs
At AirGreen, every installation includes:
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An active drainage test
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A proper slope (minimum 1 cm per meter)
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A pump if gravity alone isn’t sufficient
In Longueuil, a homeowner called us after water was leaking under a Midea wall unit. The drain had been connected to a sink pipe… with reverse slope. We redid everything and installed an automatic pump with a backflow valve.
Mistake #4: Installing the outdoor unit too close to walls or enclosed areas
The outdoor unit needs to breathe. Too often, it’s:
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Pushed up against a wall
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Placed under an enclosed balcony
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Installed in a corner with no airflow
This leads to compressor overheating, decreased performance, and accelerated wear.
Our installers always ensure:
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30 to 60 cm of clearance
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Elevation to prevent water and snow buildup
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Orientation toward a well-ventilated area
We’ve even designed custom mounts for certain Longueuil condo buildings with space constraints.
Mistake #5: Cutting corners with refrigerant and electrical connections
A poorly executed connection can:
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Leak R-32 or R-410A refrigerant, harmful to the environment and system performance
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Cause power cuts or electrical arcing
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Void the manufacturer’s warranty
AirGreen uses only CSA-certified tools, Grade A copper, and complies with all RBQ standards. Each installation includes a pressure test and final electrical inspection.
Why AirGreen installers in Longueuil systematically avoid these mistakes
At AirGreen, we think long-term. Our installers are trained to anticipate problems, adapt every project to architectural and local climate conditions, and ensure optimal year-round performance.
Our commitments:
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Accurate thermal assessments
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Equipment from the most trusted brands (Fujitsu, Gree, Lennox, Midea)
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Technical documentation compliant for rebate programs (LogisVert, Rénoclimat)
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Clean, quiet, long-lasting installations
Conclusion: What you don’t see could cost you
An air conditioner may seem to work fine at first. But behind a rushed installation often hide invisible mistakes that compromise your comfort, raise your electricity bills, and shorten your unit’s lifespan.
At AirGreen, we believe every detail matters. By mastering them all, we deliver truly high-performing HVAC systems in Longueuil and across the South Shore.
Uncertain about your current setup? Planning a new installation? Contact us for a free evaluation and experience the expertise of AirGreen—Longueuil’s go-to air conditioning specialists with no compromise.