Why is my Central Air Conditioner Blowing Warm Air?

The other day it was ninety four degrees outside. It was a typical Kansas City summer day. I was driving home from work with the air conditioner going. I pulled into the garage and walked into my house expecting to be greeted by nice cold air. Instead, the thermostat read high into the eighties.

I checked to make sure the air conditioner was on… and it was. Next I walked over to a nearby vent and put my hands in front of it. There was air blowing into the house, but it wasn’t cold. Instead it was slightly warm, some would say lukewarm. I tried shutting off the air conditioner and turning it back on, but the problem persisted. I inspected the outside unit and the inside unit but saw nothing out of the ordinary. It seemed that I was stumped.

If you’re reading this article then I can only assume that you are going through the same, if not similar, issue. When you run into warm air coming out of your vents it could be caused by a variety of issues. In order to figure out what is going wrong with your system you are going to have to do some troubleshooting. Some of this you should be able to do yourself and others you will need a professional technician.


First, let’s take a look at the things that you can check or even try to fix yourself. After all, it is always better to try and fix the problem yourself and save the expenditure of a service call and or repair.

Let’s start with the easy fix first. Have you checked your thermostat? Yes, it really could be that simple. In some cases homeowners have come home and realized that their thermostat was accidentally set to heat. (My toddler has done that before without me knowing… so don’t feel bad!)

If the thermostat is set to cool then another thing to check on your thermostat is the fan setting. Not all thermostats have this setting, but you should check yours if it has a ‘Fan’ option. Typically the fan option will have ‘Auto’ or ‘On.’ If the fan is set to ‘On,’ then that means you have the blower running constantly even when the air conditioner hasn’t kicked on. While this would account for warm air coming through your vents it would not account for a very hot home. (If it was just the fan then your house will still be somewhat cool.) Just to be safe though, I would set the fan to ‘Auto.’ When set to ‘Auto’ the fan will only come on when the air conditioner is on.

Another possible cause for the warm air blowing through your vents is an obstruction or restriction to the airflow of your system. In other words, something is blocking air flow and in most cases it is your air filter. This is the filter that you’re supposed to replace every few months. You did replace yours recently, right? If you didn’t, then this may be the cause of the warm air. Purchase yourself a new filter either at the store or online. If you are unsure what kind of filter to get check out our central air conditioner filter best of guide.

Along with swapping out the air filter inside your home you can also take a look at your outside system. How does it look? Is it covered in debris such as leaves, grass, and dirt? Are there shrubs or trees right up against it? In the case of the trees or shrubs I would either remove them or trim them back to give the air conditioner enough space. If the unit itself is looking quite dirty then you can take a garden hose on a LOW setting and gently spray the sides of the unit. When doing this ensure that you are only spraying the hose at the air conditioner’s condenser. (This is the side with the fins.) Do not spray on the top of the air conditioner. Also, be sure to turn your air conditioner off when spraying.

Service Call Causes

Well folks, we have exhausted what a homeowner can do to diagnose and fix their air conditioner that is blowing warm air. Now, we will take a look at what some of the other problems could be. While you may be tempted to try and correct some of these problems yourself I would recommend contacting a professional to ensure your safety and to also prevent you from further damaging your system.

A reason for blowing warm air that technicians come across a lot is that the outside unit isn’t receiving electricity. Remember, that you need both inside and outside units working together in order to achieve cold air and if your outside unit is no longer receiving electricity then that would explain your problem. You can check your circuit breaker to see if power is being routed to the outside unit. However, if you do notice that the circuit has been tripped or a fuse has blown then you should contact your service technician immediately. I repeat, do not try to fix yourself.

Another possible reason for your air conditioner not cooling is that the evaporator coils are dirty with dust and are having trouble absorbing heat. While it is not recommended you clean this yourself this could be causing your problem. If you schedule a yearly maintenance checkup on your air conditioner your service technician will clean these coils for you to ensure they are working in top condition. (You may have to ask for this service as not all techs will do this.) The good thing here is that if you are diligent on swapping your air filters every month or two then you will most likely not have dirty evaporator coils.

You could also be having problems with your duct work. It could be that some of your duct work has been broken or disconnected. Or, it could be that your ducts are actively leaking air. This isn’t as common of a problem, but it can happen. If not your duct work it could also be a faulty fan motor. Your fan motor is the motor that gives the power to the fan on your outdoors unit. This is the fan that expels the hot air from your home. (If you were to lean over your air conditioner while it’s on you’ll see the fan moving back and forth blowing the hot air away.)

While the above reasons can be causes as to why your air conditioner is not working they are not the most common problem that techs come across. No, the most common are the two problems listed below. The downside here is that these problems can be quite expensive to fix. Let’s take a look:

Low Refrigerant

If your system isn’t cooling your home or is blowing warm air then it is likely that it is low on refrigerant. Refrigerant is the ‘blood’ of your air conditioner. Without refrigerant your system cannot absorb the heat from your home. If you do have low refrigerant do NOT just add more refrigerant to your system. Refrigerant flows through your air conditioner in an endless cycle. In other words, you should never run out of refrigerant… unless you have a leak. If you, or your service tech, adds refrigerant to your system without fixing the leak then you are just throwing money out the door. You are going to have the same problem again when that new refrigerant leaks out.

Instead, your service tech needs to identify where the leak is coming from. Is it on the refrigerant lines going back and forth between the evaporator and the condenser? Is it in the outside unit? Or, in the inside? Once the leak has been determined the technician will patch it and then recharge your system. While the patch may not be too expensive the recharge of refrigerant can get quite pricey, especially if most of your refrigerant has already leaked out.

Also note that you may have more than one leak in your system. This can happen in the piping of older systems. Sometimes the old piping can get corroded and cause multiple micro fractures throughout the lines. In this case your service tech may need to replace the entire pipe.

Compressor Problems

The other most common problem with a central air conditioner is a bad compressor. If refrigerant is the ‘blood’ of your air conditioner then the compressor is the ‘heart.’ The compressor is what circulates the refrigerant throughout your system. If there is a problem with the compressor then it will most likely need to be replaced.

Unfortunately, a compressor replacement can be an expensive repair. It could be a couple hundred or it could be six or seven-hundred. It is hard to gauge this as there are other factors to consider. Such as what size is your air conditioner? Did the broken compressor cause other problems? Does the system need a recharge of refrigerant?

Yes, that’s right. In some cases you could have a faulty compressor and need a refrigerant recharge. If that is the case then I’m sorry to say that you’re going to have a hefty repair bill.


Hopefully this article was able to guide you in the right direction on how to fix your air conditioner. Going back to my story from above, I was able to get my air conditioner fixed. It ended up being a combination of things. The evaporator coils needed cleaning, I swapped out the filter, and I found that the blower motor wasn’t large enough for my home so the air being pushed through didn’t have much force behind it and it was having trouble absorbing heat. All of this together accounted for the warm air that I was feeling. I can safely say that today my home is back to seventy-two degrees where it should be!

If you find yourself in the position where you are facing a large repair you should always weigh the decision if you should make the repair or if you should purchase a whole new system. For example, let’s say you have been quoted twelve-hundred dollars for a compressor repair, refrigerant recharge, and some other minor repairs. Should you spend twelve-hundred dollars? Or, should you purchase a whole new air conditioner?

In this scenario I would weigh my decision on how old my air conditioner was. If it was only five years old or so then I would continue on with the status quo. However, if the air conditioner was ten or even fifteen years old then I would definitely consider purchasing a whole new system. While some air conditioners can last as long as twenty or more years you will start sinking money into it with each passing year.

Be sure to think this over before investing money into a failing machine. It is never a good feeling to invest a thousand dollars into your air conditioner only to have something else fail a few months down the road.