There is nothing quite like turning your air conditioner on and feeling your home get…hotter? An air conditioner that is not blowing cold air is a problem, but one that can be repaired.
This article will examine all the reasons an air conditioner may start blowing warm air. We will also tell you how to fix it, or if needed when to call in an HVAC professional. Everything you need to know to get cold air flowing through your vents once more is right here.
Reasons Why Air Conditioners Not Cooling & How to Fix Them
Unlike other common air conditioner problems such as freezing up or leaking water, the issue of blowing warm air isn’t a simple diagnosis. Unfortunately, there are many reasons this can happen, and the best course of action is to start going through them all, one by one.
Lack of Adequate Airflow
Inadequate airflow is one of the most likely culprits. However, several things can cause poor circulation (or none at all). Let’s start with the easiest one, the air filter.
Dirty, damaged, or clogged air filters can block over 90% of the air needed to have cool air in your home. A paper filter on a central air unit is designed to last 30 to 90-days. Once its lifespan is over, it needs to be replaced. If you smoke in the home, have pets, plants, or open the windows frequently, that life span can be even shorter.
Window models and portable ACs usually have a mesh screen filter that is washable. It should be cleaned about every 250 hours of use or once a month. If you have cleaned or replaced your air filter and the AC is still blowing warm or hot air, it’s time to check the thermostat.
Defective Thermostat or Not Set Correctly
Next, you want to check your thermostat. We know, it almost feels like telling you to check that your TV is plugged in, but weird things do happen. Smart thermostats, for example, are controlled by mobile apps and voice commands, which you can trigger on accident.
Digital and non-programmable thermostats have touch screens that can accidentally get activated. You will want to check that you are in cooling mode, not heat or fan-only mode. You also want to check that the temperature is set correctly and that the batteries (if equipped) are new, charged, and not corroded.
Once you verify the thermostat is working correctly, the easy, clean stuff is done with, and it is time to check other issues.
Dirty Condenser, Dirty Coils
Another factor of insufficient airflow can be caused by dirty condenser coils. Head outside and check the condensing unit.
You will want to look at several things while you are here. First, take a look at the two copper lines and the electric wire coming from the house to the rear or side of the condenser. The smaller copper line is (should) be quite hot to the touch, so lightly touch with the back of your finger and don’t grab it.
The larger copper line should be cold and covered in condensation (if the unit has been on for any length of time.
However, the low line (bigger copper pipe) should not be warm, dry or covered in frost or ice. If you notice any of these symptoms, you most likely have low refrigerant levels (more below).
The electric wire is the line from the thermostat. Be careful not to break it and give a slight tug to ensure it is connected securely behind the condenser panel cover. It may wiggle, but it shouldn’t pull out or come off at all.
Check the Condenser Fan
Assuming that is all well, you will want to notice if the fan is moving. You should feel a blast of warm air as you approach the condenser (if the system is on and running), and the fan should be spinning at high speeds. Do not stick anything into the condenser. You will be able to visibly tell if the fan is moving.
If the fan is not moving, place the back of your hand on the center of the condenser top (between the four bolts). It should be warm but not extremely hot. If it is extremely hot, that is a big sign that the fan motor is burned out.
Inspect and Clean the Coils
Finally, you will want to inspect the coils and condenser vents. You should be able to see the aluminum fins through the vents. If you see dirt, leaves, pine needles, and other gunk but not the fins, you need to clean the coils.
Turn the system off and remove the breaker switch for the condenser unit before you start cleaning. 240 volts is not something you want to mess with. Cleaning the coils is easily done with a garden hose and a spray nozzle. Wash all the dirt (top to bottom) until the coils are cleaned out.
To be extra thorough, you will need to remove the top of the condenser housing (leaving the fan attached) and set it up out of the way. Note that the fan wires will prevent you from removing it completely, but you can set it up out of the way. Use the garden hose to clean the inside of the coils the same way as you did the outside.
At this point, before you put it all back together, you should check the compressor.
The compressor is the black, cylindrical device mounted in the center of the condensing unit. While you have the top off to clean the coils, check the compressor.
You won’t be able to tell if it is bad by looking at it, but there are a few things you can do without tools.
First, touch the top of the compressor. Use the back of your hand to minimize burns, just in case. The compressor should be hot, but not hot enough to cause any pain.
If it is too hot, it is a sign that the compressor is not working correctly and needs to be replaced.
You will also notice three wires running to the unit. These wires are generally combined and meet in a housing clip. You can remove the clip and inspect the terminals. They should be clean and shiny. If they look burnt or corroded, it could be the reason the compressor isn’t working.
Any further diagnosis will require special tools and should be done by a licensed HVAC technician. Once all of this is tested and checked (and reassembled), it is time to head inside to the evaporator unit.
Clogged Condensation Drain
Inside the evaporator unit is an access panel. Once opened, you will be able to inspect the coils, blower fan, and condensate drain pan. There will be another panel that houses the electrical components. However, you should never access this panel unless you have some HVAC training and are sure there is absolutely no power running to the system.
A clogged drain, though, can cause the system to stop removing as much moisture from the air. Warm air is more humid than cold air, and part of the evaporation process is removing moisture from the air. If the coils are instead evaporating and condensing the drain pan water, the air will stay warmer.
You can check this by looking (or more likely reaching) and placing a finger into the drain pan. It should be near-dry and clean. If the drain is clogged, there will be water near the top of the pan lip, and it may have a muddy feeling at the bottom. You can use a wet/dry vacuum to clean out the pan and use drain pan tabs to prevent gunk build up in the future.
Frozen Evaporator Coil
Another common culprit, and easy to spot, is iced-over evaporator coils. You will notice this long before you ever put a fingertip in the drain pan. If the coils are covered in ice, it will block the airflow and prevent them from cooling the air.
However, diagnosing why the coils are iced over is a different story. Most likely, it is because of low refrigerant levels. This will mean you have a refrigerant leak and need to have the leak identified and repaired (see further below).
The other culprit could be a dirty or clogged air filter. If you have already checked the air filter and it was overly dirty, allow the ice to melt and try the air conditioner again. If the ice stays gone, it was the air filter. If the ice returns, it is likely to be a low refrigerant problem.
Faulty/Broken Fan & Fan Motor
Just as we checked the condenser fan and motor, you need to also inspect the blower fan. Unlike the condenser fan, though, the blower fan is much more challenging to get to.
However, if the system is on, the fan should be blowing. If you remove the evaporator access panel and there is no air suction (it will be loud and forceful), then the blower motor, fan capacitor, or wiring is at fault.
You will need to call in an HVAC technician to remove and test the blower fan motor and capacitor. They can also check the capacitors, connectors, and wiring in the control panel while they are in there too.
Defective Control Board
Older systems and furnaces will have a control board. This is a computer-style board that can be used for diagnostics, troubleshooting, control, and power switching. It is usually found on the air handler but can technically be placed anywhere along the system between the thermostat and condenser.
When inspecting the board, you will need to know what the various indicator lights mean. Some will blink, stay lit, extinguish or even change color based on the error code. Your owner’s manual may have a section detailing the troubleshooting features.
However, what you want to look for are burnt areas, loose connections, or broken pieces. Otherwise, it is best if a professional technician looks at and tests the board with the right sensors and equipment.
Related: How To Test HVAC Low Pressure Switch (Step By Step)
If you have made it this far in the inspection and diagnosis, it is time to call in an HVAC technician for assistance. The only other items that can cause warm air blowing from the AC are a refrigerant leak and damaged or leaking in the air ducts. Both require expert knowledge and tools to detect and diagnose.
A refrigerant leak can happen anywhere along the refrigerant lines, though it is most common in the evaporator coils, condenser coils, or the fill valves. Any bend in the piping, previous repair spots, and welding areas are also susceptible.
Even a hole that is too small to see (or even hear the escaping refrigerant) can cause enough pressure and fluid loss to freeze up the system and cause cooling to stop. An HVAC technician will come in and use leak detector equipment along the copper lines and find where the leak is coming from.
A quick brazing of the hole later, and your problems will be cured. However, it is wise to also pay for a full inspection of the system while the tech is present. This will stand-in for your annual inspection, and any other problems caused by the refrigerant leak can be identified and handled before they become major.
A Leak in the Ductwork/Damaged Air Ducts
Finally, the issue could be caused by the air ducts themselves. Usually, a damaged ducting will cause no airflow; however, if the damage doesn’t cause duct collapse, it can release the cold air and intake warm air instead.
The ducting is usually fiberboard, aluminum, or tin, nothing that is extremely tough or resilient, but it generally doesn’t need to be. The job of the air ducting is to route the cold air from the evaporator unit to the individual rooms of the home.
If they develop a hole, break open at the taped seams or have holes chewed because of pests or rodents, the cold air will escape through the cracks or holes. This cold air exit also works like a vacuum, sucking in the warm air surrounding the ducts in your ceilings and walls. That warm air then gets pushed out the vents, resulting in a warmer room.
A technician can probe and test the integrity of the entire ducting system and find any areas that are damaged or leaking. Usually, a fix only required some duct tape or a new section installed. Technically this is a DIY project, but the hard part comes in detection and access, which is where hiring a professional will save you time and money.
Fixing Defective Air Conditioners (By Type)
The various types of air conditioners will have different reasons for blowing warm air instead of cold. As such, each type will also have differing fixes and methods. We outline those differences below.
Home Central Air Conditioner not Blowing Cold Air
For home central air conditioners starting cold and then blowing warm air is generally an icing or freezing issue. The system will work correctly until the ice has time to form, resulting in warm air coming through the vents.
If the system starts warm and never becomes cold, then the issue (as noted in the above section) can be a myriad of things. The most common, though, is blocked airflow from a clogged air filter, or the compressor is not working.
If you cannot quickly and easily locate the cause of the warm air, it is always best to call in an HVAC technician. However, you should always make a few checks yourself. First, you want to change the air filter to ensure the intake airflow is unobstructed.
Next, you can check the thermostat and condenser unit. Look for icing of the lines, an overheated compressor, and a bad fan motor. If these all check out fine, open the access panel to the evaporator unit and look for ice on the coils or a blower fan motor not working.
Mini Split Air Conditioner not Blowing Cold Air
Mini split air conditioner systems are similar to central air systems using internal air handlers in each room and a single heat pump outside. The same symptoms and causes are present. However, if you have a ductless mini split system, there won‘t be collapsed ducting to worry about.
In the case of mini split systems, you have smaller filters and more of them (one for each interior unit), so this is the first thing you should check. After that, you will want to inspect the heat pump, ensure the thermostat is in the correct setting and mode, and look for ice on the refrigerant lines.
If you cannot diagnose the problem, or it turns out to be a bad fan motor or icing of the lines, it is time to call in a professional for repairs and further inspection.
RV Air Conditioner not Blowing Cold Air
RV air conditioners are notoriously hard to diagnose. Due to the compact size and nature, access to the system is virtually impossible without the right tools and equipment. However, you can check the basic stuff yourself.
Change out the filter and double-check the thermostat. Then it is time to get on the roof and look at the condensing unit. Remove the shell and inspect connections, motor and fan and look for signs of ice build-up. Domestic RV air conditioner not blowing cold air is a common condition of the popular AC brand. Usually, it is due to a refrigerant leak at the valve core stems on the refill lines.
In most cases, though, an RV blowing hot or warm air will be down to evaporator and refrigerant line leaks. Many of which will be inside the walls of the RV and will need a trained HVAC technician with RV experience to locate and repair.
Window Air Conditioner not Blowing Cold Air
Window and through-the-wall air conditioners usually have internal airflow problems that cause warm air. Still, you will want to run through the easy fixes first.
Start with the settings and controls and ensure the system is in the right mode and fan speed. Then, pull out the washable filter and ensure it isn’t dirty or blocked. After that, you want to check the intake vents on the front of the machine (remove the faceplate) and clean off the evaporator coils while you are there.
After that, you can walk around to the backside and check the condenser coils and clean off the backside of the unit, including the drain line. If the system is still blowing warm, you will need to remove it from the window and get inside.
Usually, you will find ice or pools of water. If this is the case, or you cannot find the issue, it will time to take the unit to a professional. However, before you pay for services and repairs, get a quote estimate.
Often, the labor, parts, and service fees will be higher than the cost of a new unit. If you have had the air conditioner for several years, it may be worth spending a little more and buying a newer model with better efficiency.
Portable Air Conditioner not Blowing Cold Air
When portable ACs stop blowing cold air, there are very few things you can do. Unless the unit has heating options, too, there is no reason to check modes and settings on the control panel.
Once you verify the drain pan is empty, the filter is cleaned, and the vent hose is connected properly and attached to the window, there is little else to do. LG portable fans, for example, are all internal, and most have void stickers over the access screws.
However, if the unit is still in warranty, you can make a claim and have it repaired or replaced according to the warranty conditions. If it is out of warranty, it is a lot cheaper and easier to buy a new model. Having a portable AC repaired out of warranty will cost as much or even more than a new unit, in most cases.
Car Air Conditioner not Cold
When it comes to your car’s AC blowing warm air, it may be wise to just pull into a service station to have the issue diagnosed. Many mechanics will offer free inspections and diagnosis, or will put the cost of the inspection towards the repair bill if needed.
Car air conditioners work on all the same principles of your home AC, but in a slightly different way. You also need an EPA 609 certification to work on the AC lines, refrigerant, and system.
Before you head to the dealership, though (unless the car is under warranty), you can check the cabin air filter, which is lesser-known and often overlooked. You will need to go online to find your location, but most are behind the glove box just above the blower fan.
If the cabin filter is clean or replaced and it is still blowing warm, double-check the controls on the console to ensure you are in heating mode. Beyond that, though, there isn’t much DIY checking you can do.
When is it Time to Upgrade My System?
Sometimes it is better to admit defeat and purchase a new, upgraded air conditioner system. Obviously, for residential systems, this is expensive and needs to be thoroughly thought about. For most other air conditioner types, though, it can be an easy decision.
- If the system is over 10 years old.
Central AC systems are designed to last at least 15 to 20 years. However, this wasn’t always the case. Older systems also use the R-22 refrigerant, which is no longer legal to install new. Upgrading to a newer, highly energy-efficient system that uses R-410a is a wise investment for your home.
- Problems constantly reoccur.
Some systems seem to break down each season, or you fix one problem only to discover another one. In these cases, if you are going to spend money, you may as well pay to have a new system installed. If you have a central AC system, it may be wise to upgrade to a mini split system instead. A cheaper install and better efficiency to save even more.
- High repair bills.
HVAC technicians are great, and most do a wonderful job restoring your system to like-new condition. However, they come at a cost. If you find that repairs and replacement parts, as well as labor costs, are more than you feel should be spent, an upgrade to the AC system is warranted.
Ways to Improve Air Conditioning Efficiency
One way to keep your air conditioner blowing cold is to keep up and improve efficiency. By helping the system work more efficiently and at a lower rate, you save wear and tear on the components.
- Regular cleaning and maintenance.
Most AC units require filters to be cleaned or changed every 30 to 90 days. However, beyond that, most of us don’t do much else in the form of preventative maintenance. Your entire system, including coils, fins, condenser, and evaporator, need to be cleaned annually.
- Yearly inspections.
A full air conditioner inspection by a licensed HVAC technician should only last a couple of hours. The money spent will help your system be more efficient, find and repair any problems before they become serious, and keep your mind at ease.
- Use fans.
Ceiling fans have switches for cooler and warmer weather. When used in summer mode, they will help circulate the cooler air making the temperatures stay lower, longer. Even using floor fans will help, too. If the temperature is maintained, the air conditioner has to come on and work less often.
People Also Ask (FAQ)
My AC is new, why is it not blowing cold air?
A new AC shouldn’t have any issues, but it does happen. While it is frustrating, the best thing to do is call the installer back out to investigate. Most likely the issue is a refrigerant problem, either a faulty compressor or crossed wiring. In some cases, the refrigerant valves on the condenser lines don’t get opened, or a new thermostat is wired incorrectly. The installer should be able to pinpoint the problem and get it fixed at no additional cost to you.
Why does my car AC stop blowing cold air when I accelerate?
The most common explanation is a vacuum leak. In particular, a vacuum leak on the AC damper or door lines. A service mechanic will be able to run a vacuum test line to locate and repair the problem and have your cold air blowing again in no time.
What are the symptoms of a bad AC compressor?
If the compressor is broken or going bad, you will notice many changes in your AC performance. Most notably, you won’t have cold air inside. You may also notice other symptoms that include loud banging noises, circuit breakers tripping, condenser unit overheated, no hot air being expelled from the condenser fan, ice build-up, or leaks around the condenser coils and lines, or even an overheated compressor with burnt or melted wiring connectors.
What outside temperature is too cold for air conditioners?
All air conditioners have a low limit setting. If you operate the system below this setting, it can cause problems, failure, or damage. In most cases, this setting is 60 degrees Fahrenheit, but some models are lower than this. Heat pumps, for example, can even go as low as 48 degrees.
How much will it cost to have an HVAC professional fix my air conditioner?
Home Advisor states that a typical HVAC technician call will range between $75 and $180. This cost will also go towards any repairs that are needed, in most cases. For repairs, your costs will vary depending on the parts needed, the time it takes to repair, and the region you live in. On average, though, you can expect to pay an additional $340 for the inspection and repairs.
How often should I have my AC serviced?
It is recommended that you clean the system, including evaporator and condenser coils, twice a year. You can usually do this yourself with a garden hose and a couple hours of your time. However, the entire system needs to be inspected and tested at least yearly to ensure proper operation, maximum efficiency and to find and repair any minor issues before they cause significant problems.
Turning on your air conditioner only to get warm or hot air blowing from the vents is never a good thing. However, it is also a problem that is hard to diagnose. With so many parts of an AC system that can cause it, pinning the culprit down is a challenge.
This article gave you all of the reasons that an AC would blow hot and general guidance on fixes and solutions. If you are capable of tracking down the fault yourself, that is great. However, you shouldn’t be afraid to contact an HVAC professional at any time. We have included the easy form above to help you get a quote.