Why Is Your Air Conditioner Blowing Warm Air | How To Fix It.

Why Is Your Air Conditioner Blowing Warm Air | How To Fix It

If you are asking why is my air conditioner blowing warm air then this post will help you find and fix the reason. There are several reasons why this may be happening. I will go over some of the obvious ones that are simple to troubleshoot and repair.

  • Disclaimer – Read the disclaimer at the bottom of the page.

The first mistake people make is to assume that the system is low on refrigerant. Your HVAC system may be low on refrigerant but that is not where you should start.

There are parts of the system that can become restricted and will cause the air to blow warm. Quite often a technician will connect his gauges before checking other components and tell the homeowner the Refrigerant is low.

If the indoor filter is really dirty it will cause the readings on a set of A/C Gauges to read the wrong refrigerant levels. When the evaporator coil is dirty it will cause the Air Conditioner to underperform and possibly blow warm air. The outside condenser coil also needs to be clean and free of restrictions.

  • Dirty Air Filter
  • A Dirty Condenser Coil
  • Dirty Evaporator Coil
  • Drain Line Issues
  • Refrigerant Level

The point I’m making is don’t just check or assume low Refrigerant is the reason your air conditioner is blowing warm air.

A Dirty Air Filter

A dirty air filter will restrict the airflow and cause your air conditioner to blow warm air. Sometimes the evaporator coil will freeze up when the air filter is really dirty. When this happens you will need to let the ice on the evaporator coil melt before you turn the system back on.

After you remove the clogged filter and replace it with a new one turn the system back on. If you wait 5 minutes you should feel cold air coming out of the register. If this was not the reason your air conditioner was blowing cold air then you will need to move on to the next item to look at.

Dirty Condenser Coil

Another possible reason your air conditioner is blowing warm air is that the outdoor condenser coil is dirty or somehow restricted. You should easily be able to look at the condenser coils to determine if they are dirty. Air needs to be able to flow through the coils in order for the HVAC system to function properly.

Dirty evaporator coil causing warm air to blow
Dirty Condenser Coil

If plastic gets stuck on the outside of the condenser coil or if other items such as bushes or shrubs get really close to the coil it will restrict the airflow.

If the coil is dirty you can take your hose and use low pressure to clean the coils of any debris.


High pressure will bend the coils and cause poor air flow problems. So, only use a low pressure and wash the coils off.

Don’t use any type of brush or anything like that. Local home improvement stores like Home Depot or Lowes have coil cleaner that you can use to clean the coils.

The goal here is to clean them not harm them. I have heard and seen people use products that deteriorate the coils. Make sure to use a NON-ACIDIC cleaner that’s approved for A/C coils.

After you clean the condenser coils turn the system back on and wait 5 minutes to feel if cold air is coming out of the register. If cold air is coming out then great. However, if cold air isn’t coming out then you will need to move on to the next step.

A Dirty Evaporator Coil May Be The Reason Why Is Your Air Conditioner Blowing Warm Air

Your evaporator coil is inside near your blower motor. If your evaporator coil is dirty it may cause the air to blow warm on your air conditioning system. Depending on if you have a furnace or an air handler will determine what [access covers] you need to remove to access the evaporator coil.

You are wanting to see the side of the evaporator coil that air flowing into. Whatever direction the air is flowing is the section of the evaporator coil you want to look at.

Dirty evaporator coil causing warm air to blow
Dirty evaporator coil causing warm air to blow

In some scenarios, your system may have an access door near the evaporator coil. If this is the case you can open the small access door and look at the coil.

If the coil is dirty you will need to clean it.

The same rules and methods apply to your evaporator coil as the condenser coil.

You don’t want to use any brush or anything like that. You want to use an approved cleaner and possibly a hose to clean the coil. make sure to let the cleaner sit for a while to loosen up the impacted dust.

after it sits for a while have a squeeze trigger on the end of the hose and apply a little pressure. to clean the evaporator coil.

If you take your time the water will simply go into the evaporator coil pan and drain out of the home. This way you don’t need to worry about water damaging your property.

after you have cleaned the coil you should put all of the covers back on and then turn the system on. Let the system run for a good 5 minutes to see if cold air comes out.

If you still don’t have any cold air you will need to move on to the next step.

At this point, you have cleaned the major parts and the system should be blowing cold air. If the system is not blowing cold air but everything else seems to be fully functional then it’s time to check the refrigerant level.

Drain Line Issues

Wherever your evaporator coil is located you will find the condensation drain lines. They will be white and the typical standard size is 3/4″ in size. Different systems have different configurations.

How can a drain line cause warm air to blow? I will fill you in on a little secret.

When some systems are installed they put in a safety overflow switch. this is a switch that is typically close to the evaporator coil.

When the drain line is clogged the water will back up causing the safety switch to shut only the outside condenser off. It should shut the whole system off but in this scenario they wired the system so the outdoor shuts off and the indoor keeps running.

When this happens the inside unit runs as normal but it only blows warm air. I have found this so many times on service calls.

Here is a picture of what the safety overflow switch looks like. All you have to do is take the cap off and then clear the drain line.

why is my air conditioner blowing warm air.
Overflow Safety switch

You should know if this was the problem right away because when you pop the cap off you will see water backed up.

After you clear the drain line put the safety overflow switch in place and start the system up.

If after doing all of the other steps without any cold air coming out then you clear the drain and cold air come out you know you fixed your problem.

Refrigerant Level

If all of the other attempts to fix Why Is Your Air Conditioner Blowing Warm Air did not work then you will have to connect an approved set of Gauges to get the readings on the system. After connecting the gauges you know the system is clean and should be giving accurate readings.

At this point, you will be able to determine if something more serious is wrong with your system. I hope this post helped determine why your air conditioner is blowing warm air.


* WARNING! This post and information on this website are for trained and certified technicians only. It is for educational purposes only. Under no circumstances should anyone who is not qualified or have the required permits or licensing attempt to use any information in this post to try and repair an HVAC or electrical system on their own. The opinions and methods I use are my opinions and I give no guarantee of any type of outcome. In other words, if you are not a trained and certified technician you should not attempt any repairs on your own. You should hire a licensed professional to do the work.  

*Income & Affiliate Disclaimer. If you purchase a product or service from one of the links on this page you should assume I earn an affiliate commission. Meaning I earn money because you purchase through one of my links. You should also assume that by clicking on my links you may receive email communications from me. 

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