Why Is My AC Blowing Warm Air?

10 Reasons Your Air Conditioning System Isn’t Working Properly

By James K. Kim

If your home’s air conditioning system is blowing warm instead of cool air, there could be several different reasons why this is happening.

Drawing upon our 40+ years of experience as air conditioning service and installation experts servicing homes and businesses in Westchester County, New York, we will share with you 10 reasons and potential solutions why your AC isn’t working right.

1. Low Refrigerant In The System

Perhaps the most common reason an air conditioning system blows warm air is due to low refrigerant levels.

Refrigerant gas is a necessary component for an AC unit to run correctly because it absorbs humidity and heat from the air, rendering it cold.

And as handy as you may be at handling household issues, a refrigerant problem does require the attention of an HVAC professional. That’s because this problem might have several different potential causes.

For example, your air conditioning system may have a leak somewhere within its components that is losing refrigerant. That’s why it is strongly recommended to book a service appointment with Cottam Heating and Air Conditioning for an HVAC technician to diagnose the system and offer a solution to fix the refrigerant leak.

2. Frozen Evaporator Coil

For HVAC systems that have a furnace with an attached evaporator coil for central air conditioning, impeded airflow can lead to increased air buildup within the coil.

As a result, there is a failure to properly complete the refrigeration cycle, leading to ice buildup and a frozen coil with no cold air coming from the supply vents.

An AC service and maintenance check will often catch issues like this early before they get worse (most likely on the hottest day of the year when you need your air conditioning to work).

3. Faulty Compressor

In addition to refrigerant leaks and frozen coils, the compressor (located within the outside condensing unit of a central AC system) can fail and not be able to properly work with refrigerant, leading to warm air blowing from the air conditioning unit.

Compressor issues are another high-level situation that requires the attention of a professional HVAC service technician to diagnose and fix to ensure a job is done properly and safely.

4. The Condensate Drain Is Clogged

Every air conditioning system when operating produces excess condensate water that is released through at least one drain.

If this condensate drain becomes clogged, the excess condensate water will remain inside the air conditioner, leading to potential problems including the system not turning on, inefficient operation, or blowing warm air.

During a seasonal air conditioning maintenance visit by an HVAC service technician, a checklist item on their to-do list is to clear out the condensate drain line to ensure proper flow.

5. Tripped Circuit Breaker

Since air conditioning systems use a significant amount of power, they are more likely to create an electrical surge that trips the circuit breaker in the electric panel box of the home.

When the circuit breaker is tripped, the electrical power needed to operate the AC system and cool the air is no longer available. You likely won’t get any air blowing at all from a system without power.

You can simply try flipping the circuit breaker back to its normal position and see if that restores power to the air conditioning system.

If it still is not operating, it’s possible it may have blown a fuse that requires replacement. When in doubt, it may be a good idea to call your trusted local HVAC service company to have a look.

6. Ductwork Leakage

Another common culprit of your AC system blowing warm air may not even be an issue within the unit itself.

Instead, the problem lies further down the line within the ductwork where the air travels through into air vents built into walls and ceilings.

Duct leaks allow either cool air to escape and/or warm air to infiltrate the ductwork which raises the output air temperature. Ductwork can be another tricky issue for an average homeowner to fix, especially if the ductwork is hidden within walls, ceilings, and floors.

A reputable local HVAC company should be able to provide duct repair services to pinpoint where leaks are occurring and offer a solution, such as ductwork replacement, duct sealing, or re-routing of the duct run.

7. Blocked Return Air Vents

Believe it or not, something as simple as a blocked or obstructed return air vent (that feeds warm air back into the AC system to be conditioned and sent as cool supply air) is another common reason why an AC is blowing warm.

Sometimes a return air vent is manually closed or even blocked with furniture, boxes, or whatever else may be piled up in front of them preventing proper return airflow.

Be sure the vent is open and there are no obstacles in front of it to block airflow back into the AC unit and help restore cooling supply air.

8. Loss Of Power At The Outside Condensing Unit

When the outside condensing unit of an air conditioning system loses power, it cannot properly run the refrigeration cycle. If the inside unit continues to run, it will blow warm air that has not been cooled.

If your air conditioning system is blowing warm air, try turning on the system and then seeing if the outside condensing unit is operating. If the inside unit is running but the outside condensing unit is not, it’s possible there may be either an electrical issue powering the condenser, or a component within the unit itself.

Unless you have experience and knowledge working with electricity or HVAC equipment, it may be best to call a trusted local HVAC service technician to diagnose and fix the condensing unit issue.

9. Clogged Filter

Another common reason why your AC is blowing warm air has a very simple fix anyone can do. The filters (typically located on the return air side of the unit or sometimes within the return air vent) help to prevent debris, particulates, dust, pet hair, and other materials from making their way back into the air conditioning system.

However, over time the furnace or air handler filter can get clogged and reduce airflow back into the AC system. As a result, the AC unit will need to work harder and less efficiently for decreased results and warm air blows through the vents.

The good news is this is easy to remedy for homeowners. You can simply replace the old clogged filter with a fresh one. Be sure to read your owner’s manual for the right filter size and type.

Filter changes are recommended every few months or sometimes more often depending on the indoor air quality of your home and manufacturer recommendations.

10. Thermostat Setting Error

Finally, one of the most common reasons an air conditioner is blowing warm air is due to a basic human error.

We’ve encountered homeowners who believe their thermostat is set to cool the room, but in reality, the opposite is true.

While it seems like such a small error, it inevitably can lead to much confusion and frustration when the supply air from the vents blows warm.

This is another easily fixable issue for any homeowner. Just look at the thermostat display and be sure it is set to “cool” rather than “warm”, “heat”, or “fan.” Be sure to also set the temperature slow enough to make a difference you can feel.

Call Cottam Heating and Air Conditioning to Fix Your Air Conditioner in Westchester, NY

If your home’s air conditioning system is blowing warm air and you want it fixed right, you can trust the experts at Cottam Heating and Air Conditioning to help.

Our experienced and knowledgeable HVAC service technicians will expertly diagnose the AC system issue and quickly get to work fixing it.

We also offer service maintenance plans that will help keep your air conditioning and heating systems running optimally year-round.

James K. Kim is a comfort consultant with Cottam Heating and Air Conditioning. He has over 5+ years of experience working in the HVAC industry, and specializes in helping home and business owners maintain ideal room temperatures and improve their indoor air quality. In his free time, Jim plays on two mens league ice hockey teams and two mens league baseball teams.