AC Not Blowing Cold Air (But Running): 8 Common Causes + Fixes

“My air conditioner is running but it’s not blowing cold air. What might be the problem?”

When air conditioners malfunction, not blowing cold air is one of the most common problems. There is nothing worst than looking at the AC running but not cooling (blowing 80°F or even 90°F output air temperature in the middle of summer). You’re spending electricity and sweating in your home at the same time.

About 20-30% of homeowners experience the “air conditioner not blowing cold air” problem. At first, it might seem like an inconvenience. Every air conditioner has one function; to cool your home. It isn’t not cooling your home, it’s not doing its job properly.

ac not blowing cold air is caused by warm cooling coils
Not cold enough cooling coils will cause AC not to blow cold air. There are several reasons why that might happen.

Secondly, however, the air conditioner stopping to blow cold air while still running is something to be alarmed about. AC unit not blowing cold air might be an indication of a bigger problem (compressors issues, thermostat issues, low freon levels, etc.).

If this AC problem is not dealt with properly, running an AC that is not blowing cold air might put your whole AC in danger. When central AC is not blowing cold air, for example, you want to shut it off to prevent further damage to a $3000+ unit.

Fortunately, there are a number of known causes for air conditioners not blowing cold air. They range from power issues to clogged filters, and “dirty compressors”.

Below, we have summarized the 8 most common causes of why air conditioners stop blowing cold air. Don’t worry. Any problem can be fixed, even the malfunctioning AC that’s just blowing non-cooled air.

8 Common Causes Of “Air Conditioner Not Blowing Cold Air”

We have broken down each cause into 3 sections to help you out:

  1. What part of AC might be causing the “not blowing cold air” problem.
  2. How to check which part of AC caused the indoor unit to not blow cold air.
  3. How to fix the problem (either DIY or if you need to call an HVAC professional).

In some cases, you can pinpoint the problem yourself with the help of this guide. You might want to DIY fixing the AC not blowing cold air yourself, or call an HVAC professional.

In any case, knowing a thing or two about what causes AC units to stop blowing cold air will enable to you fix the problem or expedite the whole process with an HVAC professional.

We can categorize the issues that might lead to the AC unit not blowing cold air into 3 categories:

  1. Electricity issues (power and thermostat problem; #1 and #2).
  2. Clogging issues (drains, filters, and ice buildup issues; #3 – #5).
  3. Compressor issue; #6.
  4. Airflow switch issue; #7.
  5. Low freon levels; #8.

You can check issue one by one and see if you can make the air conditioner blow cold air again:

#1 AC Not Blowing Cold Air Due To Basic Electrical Issues (Blown Fuse, Tripped Breaker)

Let’s first cover the basics. All air conditioners require access to electricity to prevent them from blowing warm air. If the compressor is not getting adequate power, it would be able to compress the R410A or R22 refrigerant. The consequence will be no heat exchange and it will result in the air conditioner blowing same-temperature air.

checking if ac isn't cooling properly due to electricial problems
HVAC professional checking the power wires in the indoor air handler (for mini-split AC unit and heat pumps).

First, check the cables. The power cable has to be correctly plugged into the outlet. Make sure you’re using the correct voltage. Smaller AC units (15,000 BTU and below) require 110/120V while bigger units will require 220/240V. Also check if any of the power cables have been damaged.

“Who doesn’t plug in their air conditioner?”

That’s the common response. The reason for check the power cables is because air conditioners require a surge of power when starting and when the rotary compressor starts working at 100%.

Everybody has an air conditioner plugged in. However, when the surge comes, two things can happen:

  1. A fuse is blown.
  2. Amp breaker is tripped.

It’s likely you won’t notice either the blown fuse or 30A breaker tripped. What you are likely to notice is that your air conditioner was blowing cold air and all of a sudden the air conditioner stopped blowing cold air.

To fix basic electrical issues that might be causing the problem, check if the fuse is blown or if the amp breaker has been tripped.

Note: Many AC units have protection against extreme power surges. They use a built-in switch when the system is about to overload. Check if that switch has been flipped. If it has, flip it back, and see if the air conditioner started blowing cold air again.

If everything works OK, check the thermostat:

#2 Faulty Thermostat Preventing AC Unit From Blowing Cold Air

The thermostat is the central hub for your air conditioners. Thermostat issues can be categorized by difficulty:

  • Basic: Thermostat is not set at adequate (below room temperature) temperature.
  • Intermediate: Thermostat has empty or almost depleted batteries.
  • Hard: The thermostat is not properly wired.

To check if the AC unit is not blowing cold air due to basic thermostat issues, lower the temperature on the thermostat to the minimum (either manually or via remote control). That should produce the lowest output air temperature from the indoor air handler; if it’s still not cooling properly, you can check the basic thermostat issue of the list.

Batteries in the thermostat can also be one reason why AC is not blowing cold air. It might sound basic but batteries in the thermostat can be quite fickle; especially when there are near depletion levels. Near depletion, the thermostat’s control panel can still show you 70°F but the battery simply lacks the energy to communicate that setting to the air conditioner unit adequately. Consider changing the batteries.

A mistake in thermostat wiring is one of the most problematic causes of the air conditioner not blowing cool air. This mostly happens with the newly wired AC unit. If your brand new air conditioner isn’t blowing cold air, it might not be properly wired, or the wires have not been properly fixed in thermostat sockets.

wrongly wired thermostat leading to ac not blowing cold air
Example of the basic 5 wire thermostat.

The reason for the new home central air conditioner not blowing cold air is most often wrongly wired thermostat. To fix it, you have to properly wire it. You can consult our guide on how thermostat wiring here (blue wire is usually for air conditioning and red R wire for power), or consult an HVAC professional to fix the thermostat problem.

#3 Clogged Drain Causing Water Builtup And Shutting Down Compressor

Every air conditioner also works as a dehumidifier. Bigger 3+ ton AC units can remove more than 100 pints of air moisture from your indoor air. All that water has to go somewhere.

That’s why air conditioners have drainage systems. The collected water is drained via a hose or a pipe. If the drain is clogged, the air conditioner will accumulate water. In essence, it will be “flooded”.

When that happens, the AC compressor – the very part responsible for achieving the cooling effect in the cooling coils – might shut down. Mind you, the fan might be working just fine. The net result will be the AC unit running but not cooling.

Fortunately, it’s quite easy to fix a clogged AC drain. You just unclog it.

Check where in your AC unit the drain piping is located. If you see debris, mold, leaves, hair, algae in that piping, make sure to remove it and clean the piping. Use household cleaning agents to clean it.

If the drainage piping is clogged and it’s almost impossible to properly clean it, you might consider replacing the drain piping in order to restore the air conditioner’s function.

When the drainage system will work properly again, the water will be able to drain out of the AC unit, the compressor will work properly, and the air conditioner should blow cold air again.

#4 Clogged Filter Switching Off The Motor; Preventing Cooling Coil To Lower Air Temperature

Every ounce of air that the air conditioner outputs have to go through the air filters. That means that the total airflow can be restricted if the filters are clogged. If the airflow is restricted, many AC parts like compressor, motor, fan, and so forth start to overcompensate to generate more airflow (to satisfy the thermostat temperature setting).

In short, “dirty filters” might sound like a small thing but it leads to serious AC issues. That’s why many air conditioners have a built-in switch that shuts the AC unit down if the filters are too clogged. This will, obviously, result in the air conditioner not working properly and not delivering the cool air output.

In some cases, it makes sense to clean the filter. In more cases, the best way of action is just to replace the clogged filters. MERV 5-12 filters used in AC units are fairly inexpensive; you can get a pack of 6 filters for about $60 (depends on your air conditioner, MERV rating, and so on).

Note: “Dirty filters” might shut off the compressor before the fan. That will lead to your air conditioner not blowing cold air while still running.

#5 Frozen Coils (Ice Buildup) Can Lead To AC Blowing Colder But Not Properly Cold Air

Ice buildup in the air conditioner is actually one of the most frequent issues we face. Basically, the parts in the interior of the AC unit freeze it as a consequence of a series of events all started by low airflow.

Low airflow can be a consequence of primarily 3 things:

  1. Clogged filters (check #4 cause). Filters directly reduce the airflow due to less space available for cold air to pass through.
  2. Dirty coils. Cleaning the coils helps in this case.
  3. Low refrigerant levels (check #8 cause).

Due to low airflow, the compressor will work extra trying to compensate for the loss of airflow, and parts of AC (primarily the cooling coil) might freeze over. The result is that the air temperature coming from the indoor air handler will be lower but not sufficiently low.

Before, the air was cooled by cooling coils with superb heat-exchange coefficient. Now, there is ice covering them, and ice might be cold but it has a much lower heat-exchange coefficient than AC cooling coils. As a result, the air output temperature might be up to 5°F cooler than room temperature; but that’s not cold enough in most cases.

Changing filters or cleaning the dirty coils is useful but it won’t fix the issue of the air conditioner blowing not blowing cold air immediately. First, you have to deal with the accumulated ice.

To get rid of the ice, just run the air conditioner with the fan on, and the cooling system off. That will melt the accumulated ice and release the cooling coils. Only after the cooling coils are out of the ice shell you can start using the air conditioner properly.

#6 Malfunctioning Compressor Due To Dirt Accumulation (Freon Not Fully Compressed)

The compressor is a vital part of any AC unit. It has one job: to compress the refrigerant (R410A, R22, etc.). The compressed refrigerant is expended in the cooling coil which cools it down; this is the basics of how air conditioners work.

If there is any malfunction in the compressor, the refrigerant is not compressed fully. This means that the cooling coil will not be as cold as it should be. The air passing through the coil will not be cooled down enough which will result in our AC not blowing the chilly cold air.

ac running but no cold air due to compressor failure
Faulty compressor will definitely lead to AC not blowing cold air but running.

Now, a lot of things can go wrong with the compressor. By far the simplest one to fix is the “dirty compressor” problem. Both central air and mini-split AC units have a compressor in the outdoor unit. There it is exposed to the elements; including mold, leaves, grass, even some animals.

All these things can dirty up the compressor and reduce its performance. When central AC isn’t blowing cold air, for example, you can check if everything is OK with your compressor.

The first order of business is to go to the outdoor unit, take off the panels, and check if there is any debris around the compressor. You might even notice an organic biofilm being formed around the compressor; that is mold and bacteria compromising your compressor.

Any HVAC professional will first clean the compressor and see if that will fix the “no cold air from AC” issue.

If not, and he or she will have a good suspicion that it’s the compressor that’s at fault, you will probably have to replace your compressor. Here are some guides on air conditioner compressor replacement costs; they can range to $3,000+ in central air units.

There are few ways that can be avoided; your HVAC professional will know best. Sadly, compressor issues usually require professional assistance. We can only DIY rough cleaning of the compressor.

#7 Condensate Airflow Switch In Off Position Due To Drainage Failure

This is a less frequent cause of central AC not blowing cold air; it might help some homeowners, however. We have already talked about the air conditioner being “flooded” when there is no adequate drainage. This mainly happens due to clogged drainpipes.

Some specific air handlers (indoor unit) have a built-in safety switch (“condensate airflow switch”) that turns the cooling off in an event of drainage failure.

You can check if that switch is turned off. That might be the reason for no cold air coming from your air conditioner.

To fix the AC not blowing cold air problem, just turn the switch back on.

Of course, you’re also recommended to investigate if there was any window AC leakage that switched it off.

#8 Low Freon Levels Can Lead To AC Not Getting Cold

Refrigerant is used to facilitate the heat-cold exchange. Without it, no air conditioner can work properly. If your refrigerant is slowly leaking from the refrigerant lines, you will start seeing your air conditioner cooling less and less.

On top of that, all other parts of the AC unit can be at harm. At low freon levels, both compressor and the motor will start working extra hard in order to compensate for the loss of refrigerant.

The only way to fix this is to refuel the freon. You might want to check our guide on how exactly to recharge an air conditioner with refrigerant.

hvac professional recharging refrigerant lines to prevent ac not blowing cold air while running

Caution: It’s best to leave the recharging of freon to HVAC professionals. It’s hard to DIY it. On top of that, you have to first find the leak, and fix it. Otherwise, the added freon will just leak out and you will, in some time, again experience the inadequate temperature of the air coming from the air conditioner.

Need A Professional Help?

These were the basics of what to look for when trying to solve the problem of air conditioners not blowing cold air but running.

For professional help, you can consult an HVAC professional in your area. If you need a bit of help finding good vetted professionals, you can fill in this form and you will get some quotes and advice for free.

4 thoughts on “AC Not Blowing Cold Air (But Running): 8 Common Causes + Fixes”

  1. Why does the colon keep blinking on the hour on the thermostat after I’ve reset the time? Shouldn’t it stop blinking after a few seconds?

    Reply
    • Hello Charlotte, that seems like an issue with using the AC. The best thing, in this case, is to open the manual; it should contain what to do in this event. Fortunately, your AC seems to be working OK.

      Reply
  2. One more thing. If outside, inspect the wiring going from wall to compressor, usually neatly cable tied to the cooling pipes. Some rat/vermin had chewed the mains to the compressor, leaving bare wire threads exposed.
    If a modern unit, and they tell you some animal like a lizard has got in and urinated the PCB so the repair is uneconomical, don’t believe them. Often it is a bulging power supply capacitor, hidden underneath the larger main pcb. Any universal 5 12v DC supply can be substituted.

    Reply
    • Hello Peter, thank you for the addition. It will surely help somebody who has a wiring problem and as a consequence, the AC is not blowing cold air.

      Reply

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