Is Your AC Blowing Hot Air? Here’s What Might Be Wrong
By Duct Professor Heating & Cooling - May 16, 2025
There’s nothing worse than turning on your air conditioner on a hot day… only to feel warm air blowing through your vents.
If your AC is blowing hot air instead of cooling your home, don’t panic — it’s a common issue, and in many cases, it’s fixable without needing a full replacement.
In this blog, we’ll break down the most common causes of this problem and help you figure out what to check, what you can do, and when it’s time to call in the pros.
- Your Thermostat Settings Might Be Wrong
- Is it set to “Heat” instead of “Cool”?
- Is the fan set to “On” instead of “Auto”?
- The Outdoor AC Unit Isn’t Running
- A tripped circuit breaker
- A blown fuse
- A failed capacitor or compressor
- Outdoor unit blocked by debris or dirt
- You Might Have a Dirty Air Filter
- Warm air is blowing from vents
- AC is running nonstop, but not cooling
- Frozen coils (which makes things worse)
- Your Refrigerant Levels Are Low (Or Leaking)
- Hissing or bubbling noises
- Ice forming on the outdoor unit or the indoor coil
- There’s a Bigger Mechanical Issue
- A failed compressor
- Faulty control board
- Broken motor or fan
- Leaking ductwork pulling in hot attic air
Before diving into repairs, check your thermostat.
When the fan is set to “On,” it keeps blowing air even when your AC isn’t actively cooling. That can make it feel like warm air is coming out, even though the unit is fine.
Quick Fix: Set the thermostat to “Cool” and the fan to “Auto.” Give it 5–10 minutes to see if the air cools.
Your indoor unit might be pushing air, but if the outside condenser unit isn’t working, the air won’t be cooled.
Common reasons:
Quick Fix: Check your breaker box for a tripped switch. Also, inspect around the unit to make sure nothing is blocking airflow.
A clogged air filter can restrict airflow, causing your AC to overheat and shut down the cooling cycle, even though the fan keeps running.
This often leads to:
Quick Fix: Replace your air filter if it’s dirty or hasn’t been changed in the last 30–90 days.
Low refrigerant = no cooling.
If your system is low on refrigerant, it can’t absorb and release heat properly, so your air comes out warm, and the system may run constantly without cooling anything.
You might also notice:
Don’t try to fix this yourself. Refrigerant issues should always be handled by an EPA-certified technician.
If none of the above apply, you might be dealing with:
These problems need a professional HVAC technician to diagnose and fix. The longer you wait, the more damage could occur — and the hotter your house gets.