Why Is Your Wall-Mounted Heat Pump Blowing Warm Air All Summer Long? (Simple Solutions)

A Common Problem in Montréal, Laval, and Surrounding Areas: What to Do When Your Wall-Mounted Heat Pump Only Blows Warm Air While Cooling

In the middle of summer, as temperatures soar across Montréal, Laval, Longueuil, the North Shore, or the South Shore, your wall-mounted heat pump should be working hard to cool your living space. And yet, many clients contact us because their unit only seems to be blowing warm air, even when cooling mode is clearly selected. It’s a frustrating malfunction, but often one that’s easy to diagnose—if you know what to look for.

At AirGreen, we’ve resolved dozens of similar situations. In this article, we’re sharing field-tested insights, the most common HVAC installation mistakes, and the concrete solutions we’ve implemented across the Greater Montréal region.

Incorrect Remote Settings: The Most Overlooked Cause

It might sound basic, but many of the cases we’ve handled in Montréal or Longueuil were simply due to remote control misconfiguration. Here’s a quick checklist of settings to verify:

• Is the unit set to “Cool” mode instead of “Auto” or “Heat”?

• Is the temperature set low enough to trigger the compressor?

• Is the fan speed compatible with proper cold air production?

In Saint-Hubert, a client was unknowingly using “Auto” mode in summer, causing the unit to flip between heating and cooling based on the ambient temperature. The result? Constant warm airflow. After a quick visit from one of our technicians, the issue was resolved instantly.

Clogged Filter or Coil: A Common Cause of Poor Performance

Dust buildup in the filters or on the evaporator coil will reduce your unit’s ability to extract heat. When that happens, the air it blows out will feel warm or barely cool.

In Laval, a customer with a Fujitsu KZAH 12,000 BTU wall-mounted heat pump noticed a serious drop in performance during the summer. During our inspection, we found that the filter had never been cleaned since the installation. After a full cleaning, the system immediately started delivering cold air again.

Our recommendations:

• Clean your filters monthly during the summer.

• Schedule a professional HVAC maintenance at least once a year.

• Visually inspect the indoor unit for any visible dirt or blockages.

Low Refrigerant or a Slow Leak

One of the more serious—but also more common—technical problems is a refrigerant leak or simply not enough refrigerant. Without sufficient refrigerant, the heat pump can’t produce cold air, even if everything seems to be working.

In Blainville, a homeowner with a Gree Lomo 9,000 BTU installed two years earlier noticed it was only blowing warm air. Our diagnosis: a micro-leak in the exterior line, invisible to the naked eye. Once detected, sealed, and refilled, the system regained full performance.

Poor HVAC Installation: The Silent Cause of Inefficiency

Improper placement of the wall-mounted unit or incorrect tilt can lead to drainage issues, airflow restriction, or thermal dead zones. These aren’t always immediately visible, but they often become noticeable during extreme heat.

At AirGreen, we were called in to Brossard to correct an installation of a Midea25 12,000 BTU that had been done by an uncertified contractor. The indoor unit was mounted too close to the ceiling, which prevented proper circulation of cold air. Once repositioned, comfort returned within minutes.

Undersized or Mismatched Heat Pump for the Space

Every home is different. Installing a unit with insufficient BTU capacity for the space to be cooled is a critical error. The system ends up running constantly, never reaching the set temperature, and creates a sensation of warm airflow.

Real-world example from Repentigny: a family had a 9,000 BTU unit cooling a 1,100 sq. ft. open-concept space. Result? Overloaded system, warm air, high energy use. We recommended a Fujitsu KZAH 18,000 BTU, eligible for a $1,704 LogisVert rebate, and perfectly suited to the space.

Customer Testimonial: Problem Resolved in One Hour in Longueuil

Mr. R. from Longueuil contacted us about his Gree Lomo wall-mounted heat pump that had been blowing warm air for three days. After a quick diagnosis:

• Filters were clogged

• Refrigerant level was low

• Indoor unit was slightly tilted inward

Our technician fixed everything in under an hour. Since then, no issues—even during the worst July heat waves.

Simple Steps You Can Try Before Calling an Expert

Before reaching out to a professional like AirGreen, here are some easy things you can check yourself:

1. Verify your remote control settings

2. Thoroughly clean the filters

3. Ensure the indoor and outdoor units are not obstructed

4. Listen for unusual noises (clicks, vibrations, irregular airflow)

5. Use a thermometer to test the air temperature coming from the unit

If the air is still warm after these checks, it’s best to contact a certified HVAC professional, like the team at AirGreen, who is licensed by the RBQ.

Why Choose AirGreen to Diagnose and Resolve This Type of Issue?

Because we deal with these cases every week. Because we know the models, the symptoms, and the solutions. Because we are local and available across Montréal, Laval, Longueuil, the North Shore, and the South Shore.

We guarantee:

• A clear, fast diagnosis

• Accredited and experienced technicians

• Quick service within 48 hours

• Complete transparency on causes, costs, and repairs

Trust our expertise to bring back truly refreshing air, even during the hottest summer days.