If your air conditioner is running but not cooling your home, you’re not alone. It’s a frustrating issue that often signals a system problem. Here are the four main reasons for your AC blowing warm air and what to do about it.
Central Air Conditioners are designed to remove heat and humidity from inside your home. The system consists of an evaporator coil located in the plenum above the furnace, a condenser unit located outside and refrigerant lines to connect the evaporator coil to the condenser unit.
The evaporator coil removes humidity, and there is a drain pipe from the coil connecting to either a floor drain or a condensate pump. This drain pipe must be kept clear, or flooding may occur around the furnace. The refrigerant lines carry a refrigerant gas (R22 if older, or R454B and R410A if newer) that collects the heat from inside the house and transfers that heat to the condenser outside. The condenser unit consists of a condenser coil to carry the refrigerant gas, a compressor to pump the refrigerant through the system and a fan to draw the outside air through the coil.
Now, here is where things can go wrong...
When summer comes, you may rely on the cooling powers of your AC to get you through those long, hot days. But what happens when that’s no longer an option? The only thing worse than a broken AC is one that won’t blow any cold air.
There may be several reasons why your air conditioner is working but not cooling, or why your AC is running but not blowing air. Let’s take a closer look at some of the reasons below and how to follow some simple steps to get your AC back up and running.
Often, the simplest culprit is the thermostat. Make sure the thermostat is set to the cooling mode, and you may want to set your fan setting to “on” instead of “auto”— warm air will circulate even when the AC is running. A mis-set temperature (higher than room temp) also prevents cooling. Faulty wiring or dead batteries can also cause erratic behaviour. Always verify your thermostat mode and temperature settings first.
So, try resetting your thermostat and programming the temperature a few degrees cooler than your house, say 20°C if your home is registering as 25°C. Wait a few minutes and put your hands over the vents to see if you can feel any cool air. It may have just needed a simple reset.
If the outdoor unit isn’t receiving power, you may notice your indoor fan running while no cooling occurs. Reset breakers and check the disconnect switch regularly. If you still don’t feel any cool air, there could be an internal wiring problem or a number of other issues, which you will need to fix with the help of a professional.
When air can’t move freely through your system, evaporator coils can’t absorb enough heat. Dirty or clogged filters are a common airflow obstacle, causing the system to overheat or freeze and blow warm air through vents instead. Regular filter checks and replacements (every 1–3 months) are essential.
Closed or blocked return vents, dirty evaporator coils, and obstructed ductwork also contribute to airflow problems. Make sure vents are open, clear, and free of dust buildup to allow proper circulation.
If your filter is dirty, switch it for a new one and get into the habit of doing this monthly if it’s a 1” disposable filter, or every 6 months to a year if it’s a media filter.
Refrigerant is the lifeblood of your cooling system. It absorbs heat and allows your AC to cool your home. When refrigerant levels drop, heat transfer becomes inefficient, and your AC will blow warm air. Signs of a refrigerant leak include hissing sounds, ice buildup on refrigerant lines, and longer-than-normal cooling cycles.
Refrigerant does not get used up like gas in a car. Low levels mean you likely have a leak. Only a licensed HVAC technician should locate and repair leaks, as well as recharge your system to restore proper cooling. If you think you may have a leak, stop using your AC immediately and contact a professional to have it inspected.
If evaporator coils get too cold, they freeze over and can’t absorb heat effectively. Ice buildup typically begins when airflow is restricted or when refrigerant levels are low. Once frozen, air blowing across the coil warms instead of cooling.
To address this, turn off the AC and switch the fan to “on” to thaw the coils. If it continues to freeze, it’s time to schedule a maintenance visit. Persistent icing often points to underlying issues needing professional service.
Evaporator coils will also get dirty over time. This can affect the overall performance of your AC and make it harder for it to remove warm air. It could end up overheating and shutting off, resulting in your AC running but not blowing air at all.
Evaporator coils should be cleaned by an experienced HVAC professional.
If your AC is blowing warm air:
Keep up with regular maintenance to avoid unwanted breakdowns and unnecessary problems from occurring. Contact Appleby Systems for professional help with your AC today and avoid being left with an air conditioner that does not blow cold air this summer!
