Symptoms you should never ignore to protect your indoor comfort and avoid costly repairs
At AirGreen, we know that central air conditioning plays a crucial role in your day-to-day comfort in Montreal, Laval, Longueuil, the North Shore and South Shore. Yet, many homeowners ignore the warning signs their AC system is sending when it starts to fail. If left unaddressed, these red flags can quickly turn into major breakdowns, expensive repair bills, or even full system replacements.
In this article, we guide you through the 9 most common signs that your central air conditioning is in distress, while sharing our hands-on experience from countless service calls across Greater Montreal. Each sign comes with real advice, true service stories, and practical solutions provided by our certified technicians.
1. Warm or insufficiently cool air blowing from the vents
One of the first obvious warning signs is when your central air conditioning no longer cools effectively. Whether the air feels warm or simply not as cool as usual, this may indicate:
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A refrigerant leak (often R-410A or now R-32 in newer models).
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A struggling or failing compressor.
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A clogged heat exchanger.
During a recent service call in Brossard, a client reached out to us with this exact issue. We identified a leak in the indoor coil line. Our team repaired it, conducted a pressure test, and refilled the system with R-32, while also cleaning the indoor unit, restoring optimal performance.
2. Unusual noises coming from the system
Squealing, banging, clicking or hissing sounds are never to be taken lightly. These noises could be caused by:
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Loose or failing parts (fans, motors).
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Worn-out bearings.
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Vibrations due to poor alignment.
In Laval, we responded to a Lennox unit where the homeowner reported a loud scraping sound at every startup. The cause: a misaligned blower motor damaging the fan blades. With a quick replacement and professional realignment, we brought back the silence.
3. Unexplained spikes in your electricity bill
A noticeable rise in energy use without any major change in habits is a direct sign your system is overworking for underwhelming results. This could stem from:
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A clogged air filter.
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An inefficient compressor.
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A malfunctioning thermostat.
For a client in Saint-Eustache, our energy audit revealed an aging compressor in a 12+ year-old Goodman unit. We replaced it with a more efficient, energy-saving model (Bosch BOVA-60HDN1-M20G), leading to a 24% drop in their electricity bill within a month.
4. Excess humidity or poor indoor air quality
A well-maintained central AC system helps maintain balanced humidity levels and ensures clean indoor air. If you notice:
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Excess condensation near air vents.
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Musty or stale odors.
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Visible mold around the ducts.
This could point to drainage issues, a clogged filter, or dirty ductwork. In Longueuil, we performed a full ventilation system cleaning, replaced the condensate tray and HEPA filter, and sanitized with UV treatment to ensure purified air throughout the home.
5. Short or irregular cycles
A unit that turns on and off frequently (known as short cycling) puts excessive stress on components and shortens their lifespan. Possible causes include:
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Poorly positioned temperature sensor.
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Compressor overheating.
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Refrigerant leak.
In Montréal-Nord, a homeowner reported erratic cycles. After a thorough diagnostic, we repositioned the sensor and adjusted their smart Ecobee thermostat to stabilize the cooling cycles.
6. Bad smells coming from the air vents
Burning smells, melting plastic odors or moldy scents are serious signs you should never ignore. They could indicate:
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An overheating motor.
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Water infiltration in the ducts.
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Bacterial buildup.
We recently completed a full duct disinfection in Repentigny after a persistent odor. Installing an ionizing air purifier eliminated the issue and improved air quality for the long term.
7. Weak airflow or ineffective vents
If air barely comes out of the vents despite a properly set thermostat, the causes might include:
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A worn-out blower fan.
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Damaged or obstructed ducts.
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A unit not properly sized for your home.
On a call in Sainte-Julie, we discovered that 30% of the ductwork was partially blocked by insulation material from a poorly done renovation. Targeted duct cleaning and recalibration restored optimal airflow.
8. A thermostat that doesn’t respond properly
If your thermostat seems unresponsive or displays inaccurate temperatures, it could be due to:
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Electronic malfunction.
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Wiring problems.
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Incompatibility with your current unit.
We recently upgraded an old mechanical thermostat in Verdun with a smart Honeywell Wi-Fi model. Beyond fixing the temperature issues, the client now enjoys remote access and real-time energy tracking.
9. Visible leaks or water pooling around the indoor unit
Water leaks could signal blocked drainage or more serious issues like:
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A cracked condensate pan.
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A clogged drain line.
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Poor initial installation.
A client in Boisbriand called us urgently after noticing water pooling beneath their unit. Our swift intervention included replacing the drain pipe and re-leveling the evaporator coil to prevent future problems.
Why call AirGreen at the first warning signs?
As trusted experts in HVAC across Montreal and surrounding areas, we know that prevention is better than cure. Our teams respond quickly with custom solutions backed by years of field experience, advanced diagnostics, and strict compliance with industry standards.
We offer preventive maintenance plans that detect these symptoms before they become critical. Every service call comes with a detailed report and tailored advice.
Practical tips to extend the life of your central air conditioning
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Get your system serviced at least once a year.
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Clean or replace filters every 3 months.
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Monitor the condition of ducts and vents.
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Install a smart thermostat to maximize efficiency.
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Call a professional as soon as you spot any of these warning signs.
AirGreen: your trusted partner for performance and comfort
At AirGreen, we’ve helped hundreds of clients in Montreal, Laval, Longueuil, the North Shore and South Shore restore their central air conditioning systems to peak performance. Our certified technicians are with you every step of the way, from diagnosis to repair to deep system cleaning, always offering reliable, human-centered service with transparency.