Why Is My AC Blowing Warm Air? 10 Common Causes & Fixes for Ontario Homeowners

Nothing is more frustrating than cranking up the AC on a hot summer day, only to be met with warm, stale air. If your AC is blowing warm air, you’re probably wondering: What’s causing this issue? The truth is, there are several possible culprits, ranging from minor fixes to major system failures.

At LG Home Comfort, we’ve seen it all when it comes to air conditioning troubles across Ontario. To help you troubleshoot the problem, we’ve compiled the top 10 reasons your AC is blowing warm air—along with practical solutions to get your home feeling cool and comfortable again.

1. Low Refrigerant Levels

Refrigerant is the lifeblood of your air conditioning system. It absorbs heat from the air inside your home and releases it outside, allowing your AC to produce cool air. If your system is running low on refrigerant, it won’t be able to cool your home properly, leaving you with hot air from the air conditioner.

Possible Causes:

• A refrigerant leak in the coils or lines
• Poor AC maintenance leading to undetected leaks
• Improper refrigerant charge from a previous repair

Solution:

Low refrigerant is not a DIY fix. Since refrigerants require specialized handling and proper disposal, it’s crucial to call a certified HVAC technician. If you suspect a refrigerant leak, contact LG Home Comfort for professional AC repair in Ontario. Our certified technicians will diagnose the issue, repair any leaks, and recharge your system with the right amount of refrigerant.

Read More: Eco-Friendly Refrigerants in HVAC: A Sustainable Revolution!

2. Clogged or Dirty Air Filters

A dirty air filter is one of the most overlooked causes of AC inefficiency. When dust, dirt, and debris clog your filter, airflow is restricted, making it harder for your system to cool your home. This not only leads to an AC unit blowing warm air but also puts unnecessary strain on your AC unit, potentially shortening its lifespan.

Signs of a Clogged Filter:

• Reduced airflow from vents
• Increased dust in your home
• Higher energy bills

Solution:

Check your air filter monthly and replace it every 1–3 months, especially during peak cooling season in Ontario. If you have pets or allergies, consider upgrading to HEPA or electrostatic filters for better air quality. A clean filter ensures proper airflow and keeps your AC from blowing warm air.

3. Incorrect Thermostat Settings

Sometimes, the problem isn’t with your AC at all—it’s with the thermostat. If your thermostat is set incorrectly, your air conditioning unit may be blowing warm air instead of cool air.

What to Check:

• Make sure the thermostat is set to “cool” and not “heat” or “fan” mode.
• Ensure the temperature is set lower than the current room temperature.
• If you have a programmable or smart thermostat, check if it’s following an unexpected schedule.

Solution:

If your thermostat isn’t responding correctly, try replacing the batteries or resetting it. If the problem persists, consider upgrading to a smart thermostat installation from LG Home Comfort for better efficiency and control. Smart thermostats can optimize cooling schedules, reduce energy costs, and even detect system inefficiencies.

Read More: How Smart Thermostats Save Energy and Money!

4. Frozen Evaporator Coils

Your AC’s evaporator coils are responsible for absorbing heat from your home’s air. However, if they get too cold, they can freeze over, preventing them from doing their job properly. When this happens, you may experience your air conditioner blowing warm air instead of cool air.

Common Causes of Frozen Coils:

• Restricted airflow due to a dirty filter
• Low refrigerant levels
• Running your AC too long without a break

Solution:

Turn off your AC and let the coils thaw. Check for dirty air filters and replace them if needed. If the issue persists, it’s best to schedule an AC maintenance service with LG Home Comfort to prevent further damage.

5. Power Issues with the Outdoor Unit

Your AC system has two main components: the indoor unit (air handler) and the outdoor unit (condenser). If the outdoor unit loses power but the indoor blower continues running, your system will push hot air from the air conditioner through your home.

How to Troubleshoot:

• Check if the outdoor unit is running. If not, it may have lost power.
• Inspect the circuit breaker to see if it has tripped.
• Look for signs of electrical issues, like a burnt smell or humming noise.

Solution:

If resetting the breaker doesn’t work, call LG Home Comfort. To prevent future power-related issues, consider installing a surge protector for your HVAC system.

6. Leaky or Damaged Ductwork

Leaky air ducts can drastically reduce cooling efficiency. If there are gaps, cracks, or disconnected sections in your ductwork, cool air may escape before reaching your rooms, while warm air from attics or crawlspaces seeps in, making it feel like your home AC unit is blowing hot air.

Solution:

Schedule a duct inspection and sealing service with LG Home Comfort. Our experts will find and fix leaks to improve your AC’s efficiency and reduce energy waste.

7. Blocked or Closed Return Vents

Your home’s return vents play a crucial role in circulating air through your AC system. If they’re blocked by furniture, rugs, or household items, airflow is restricted, leading to inefficient cooling.

Solution:

• Make sure all return vents are open and unblocked.
• Avoid placing furniture directly in front of vents.
• Clean vent grilles regularly to remove dust buildup.

8. Malfunctioning Compressor

The compressor is the heart of your air conditioning system. If it malfunctions, your air conditioner may be blowing hot air instead of cool air.

Solution:

A broken compressor is a serious issue that requires professional repair or replacement. If your AC is older, you might benefit from a new energy-efficient air conditioner installation with LG Home Comfort. Check if you’re eligible for Ontario energy rebates when upgrading to a high-efficiency AC unit.

9. Tripped Circuit Breaker

Ontario homes experience power fluctuations, especially during hot summers when many households run their ACs at full blast. If your AC trips the circuit breaker, it could be due to an electrical surge, an overloaded circuit, or an internal AC issue.

Solution:

• Reset the breaker and see if the issue persists.
• If the breaker keeps tripping, call an HVAC technician to inspect for electrical problems.

10. Clogged Drain Line

Your AC removes excess moisture from the air through a condensate drain line. If this drain becomes clogged, water can back up, triggering a safety switch that shuts down the cooling process, leaving your AC blowing hot air.

Solution:

Check for visible water leaks near your AC unit. If you suspect a clogged drain, schedule an AC tune-up with LG Home Comfort to clean and clear the blockage.

Stay Cool with LG Home Comfort’s Expert AC Services in Ontario

If your AC is blowing warm air, don’t suffer through the heat—LG Home Comfort is here to help! Whether it’s a simple filter replacement or a major system repair, our expert HVAC technicians provide fast, reliable, and affordable air conditioning services across Ontario.

✅ 24/7 emergency AC repair
✅ Expert troubleshooting & maintenance
✅ Energy-efficient AC installations & rebates