Central Home AC not blowing cold air

It is summertime, and the temperatures are extreme. You tried to go outside, but it was just too warm. So you decide to go back inside, but you still feel warm. Your last option is to turn on the air conditioner to beat the hot weather.

After turning it on, cold air was not coming out of the unit. It turns out it has some technical issues. You called for professional help. While waiting, you wondered what could have gone wrong.


The most common reason a central home AC does not blow cold air is that it’s low on refrigerant. Secondly, another reason includes that the evaporator coils could be frozen.

In this article, we’ll also take a look at the following:

  • A good leak detector
  • Checking the filters

Table of Contents

picture of an air conditioner

Troubleshooting: The most common reasons a central home AC not blowing cold air

Refrigerant levelsFan problems
Dirty coilsThermostat issues
Dirty filtersLeaking ducts
Clogged drains 

It is normal for appliances to encounter problems sometimes. By nature, electronic products will only last you a certain number of years. Within those years, it may or may not break down. It usually depends on how often you use it and how much care you put into it. 

Here are a few troubleshooting steps you can take if you have any of these issues and find the most common reasons a central home AC is not blowing cold air. In this manner, you can determine if you fix the issue by yourself or if you need to call for professional help. 

Evaporator coils are frozen.

The refrigerant runs through the evaporator coils. When hot air passes through the evaporator coils, the coils extract the hot stuff. For these coils to work properly, warm air has to revolve around the coils.

If it does not get enough heat, a thin layer of ice will form. It will cause the evaporator coils to freeze. The effect of frozen evaporator coils is the inability of the central air unit to produce cold.

If you encounter a frozen evaporator coil, turn it in immediately and seek help from a professional.

Refrigerant is low

The refrigerant is a substance that runs through the evaporator coils and is responsible for removing heat from the air that passes through it. The most common reason your unit has a low refrigerant level is leakage from the refrigerant lines.

If there is a low refrigerant level, it is unable to cool. Call for professional help right away when this happens. Fixing a low refrigerant problem does not only involve replacing the refrigerant. It also involves looking for the source of the leak and repairing it. 


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Problems with the fan

It uses a fan to cool indoor air by bringing it to the evaporator coil. Another fan then blows it to the condenser, taking the heat outside the room.

If at least one of these fans is not working properly, you will have issues. The common reasons these fans won’t work well are too much dirt.

Belts that have worn out or a defective motor can also be the reason. So can a lack of lubrication. If left unattended, it could cause major problems such as the complete breakdown of the compressor. 

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Condenser coils are dirty

The condenser coil found in the outdoor part expels air. When dirt covers the condenser coil, heat transfer is affected. It will result in the coils not working well.

If the unit is to operate, wearing various parts of the unit will increase. It may also lead to a complete system failure. 

Problems with the thermostat

A problem with the thermostat may lead to an inaccurate temperature setting. It may also not be able to main the set temperature in the thermostat. It will result in a temperature above or below the set one.

In most cases, a thermostat is easy to fix. You can do it yourself. If you use a manual thermostat, you may check the instructions manual for the correct settings. If you are using a new thermostat, you can easily reprogram the thermostat. 

Filters are dirty

Dirty filters will block air from flowing freely, which results in low flow. It may also inadequately cool the room as the AC struggles to meet the set temperature.

While it struggles, it will draw more electricity to reach the set temperature. It causes your energy bills to go up.

To address this issue, you can gently remove the filter if it is removable. Gently remove large debris by hand, and wash off dirt and other small elements with a low-pressure hose.

Other removable filters are also replaceable. It is best to check with the make and model. If the filter is not removable, gently spray water through the filter. Avoid any form of damage.

Ducts are leaking

Cooled air distributes to the entire space via the ductwork, which runs through ceilings and walls. Leaking in the ducts may occur in a hole or when the duct breaks.

A decrease in temperature may happen because the cold air can escape the leaks. Immediately call for professional care to set an appointment to fix it soon. 

Drains are clogged

As converting warm air to cold happens, it produces moisture. This moisture drains through a drain line.

The drain line will eventually clog. It means moisture coming from the air conditioner will have difficulty flushing out. In worst cases, moisture may back up and cause damage to your system.

Insert it inside the drain line and gently brush it using a stiff steel brush. You can use a vacuum to suck in the dirt for dirt that is a little bit inside. 

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Reason for AC not blowing cold airSolution
Clogged condensate drainClean the condensate drain.
Compressor malfunctionReplace or repair the compressor.
Dirty air filterReplace or clean the air filter.
Dirty condenser coilsClean the condenser coils.
Frozen evaporator coilTurn off the AC. The coil needs to thaw.
Low refrigerant levelsHave a professional add refrigerant.
Thermostat malfunctionReplace or repair the thermostat.

The outside part is not turning on or running, but the inside is

In the outdoor unit, you can typically find a switch. Make sure that the switch is not in an off position. If this switch is off, the outdoor unit will not receive any power. 

Some units have a tripped pressure switch, which triggers when the refrigerant reaches a low level. As a result, the power to the outside unit gets interrupted to prevent any damage from happening.

Call a professional as soon as possible and schedule an appointment when this happens. The technician will check for leaks in the linings before adding refrigerant.

Another possible reason it is not turning on is an issue with the thermostat. Inspect the thermostat and make sure there is a display. If it does not, change the batteries with a new one.

After changing the batteries and there is still no display, you might be experiencing another issue with the thermostat. You can either replace the thermostat with a new one or schedule an appointment with a professional technician.

Lastly, the drain line may have clogged. It will trigger a safety alert to the outdoor unit, immediately halting operations.

The compressor is not working, but the fan is running.

If you can hear or see the fan running, the compressor is not functioning. It’s the outdoor part that may not be receiving power. There are no problems with the unit, which is why the fan continues to run.

Check the wirings that connect the outdoor and indoor units. The problem may be a tripped circuit breaker or a faulty fuse.

Do you know if you have one of these?

  • Low refrigerant
  • A malfunctioning thermostat
  • Dirty condenser coils

Time needed: 5 minutes.

How do I reset the AC?

  1. The first step in resetting the system is to switch off the unit.

    For a detailed guide on how to turn it off, refer to the manual. It differs depending on your make and model, so be sure to check before proceeding. Properly switching it off is an important safety step, which you should not skip. 

  2. After switching it off, look for the circuit breaker box.

    This box links to the AC unit, which you should also switch off. Typically, the breaker box is in hidden areas. It could be in the closet or the basement.

  3. Count 60 seconds after switching off the circuit breaker box linked to the AC.

    Then switch on to let power through. It will perform its internal reset. Switch it back on after going through all these steps.

How does an AC work?

An air conditioning system is an important house appliance, especially during extreme temperatures brought by the summer season. Several households have at least one at home, which only shows how much people value it.

Although converting warm air to cold may sound like a straightforward thing to do, it is not. In reality, several processes are involved in artificially producing cold air. Everyone appreciates that during warm months.

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Think of a system like a refrigerator for the entire house. Cold air passes through the vents in a refrigerator and evenly distributes throughout the unit. The same happens in the central air system.

ac vent

The principle behind it is transferring heat from one place to another while creating cold simultaneously. The furnace cabinet is the place that receives the cold air. A blower in the cabinet transfers it to the different parts of the house. 

The cabinet is typically large and noisy. It is advisable to place it in a location out of the way and is not usually accessed. So if the cabinet is far, how is cold air transferred? It is from the furnace cabinet and is distributed through the entire house via ducts.

Being able to control the temperature inside the house is important. Having a continuous supply of cold air for an indefinite period is inefficient. Coupled with the ambient temperature, it could lead to uncomfortable levels of coldness.

Thermostats found in the house make the unit efficient. It ensures the temperature maintains at the desired level by adjusting the amount of cold air it delivers.


Let us dig deeper into the thermostats. A series of events will happen when the thermostat asks the air conditioning system to adjust its temperature.

The air-handling component draws from different parts of the house. It passes through the return ducts equipped with several filters to remove unwanted elements. It then returns to the rooms.

Now that we know how a central air conditioner handles certain processes, we move to how it processes the air to make it cold. Regardless of the brand, your unit will always have a compressor and a condenser. It also has an evaporator.

The compressor and condenser connect to an indoor furnace cabinet that houses the evaporator for a central air conditioning system. These components are found outside.

The evaporator connects with the condenser through copper tubing. The copper tubing has refrigerant, which circulates between the condenser and evaporator.

As the refrigerant moves through the copper tubing, it changes its liquid to gas as it receives and releases heat. The effect is the increase and decrease in temperature.

Warm air from the air handler passes through the evaporator coils. The refrigerant absorbs heat from the air, which converts it to vapor. Vapor now makes its way to the outdoor compressor and undergoes pressurization as it moves through the outdoor coil.

The heat quickly passes through thin metal fins, which help in dispersing heat. An expansion device makes the refrigerant cold by converting it to a low-temperature, low-pressure liquid. It then returns to the indoor coil and out to the room. This entire process goes on for as long as it is running. 

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outside air conditioner

Why is it not cooling the house, and what to do?

Thermostat not onIs the outdoor part dirty?
Filters are dirtyIssues with the circuit breaker

When the temperature set on your thermostat is 75°F, you would expect it to blow cold air. When you went close to feel the air, it did not feel cold at all. It is running but is not blowing some cooled stuff, which is not normal if it won’t cool below 75°F.

Before anything else, check if you have a heat pump or not. Heat pumps can do cooling and heating, while air conditioners cannot. It could be in heating mode, which causes the heat pump to not cool. In most cases, you will have to call a professional technician to check it. 

Before calling a professional, you can try a few steps to make sure you do need professional help. Sometimes, at least one of these four steps can resolve an issue with a problematic unit.

Here are some of the things we’ll take a look at:

  • Dirty filter
  • A dirty outside unit
  • Tripped circuit breaker
central AC

Is your thermostat switched to ON?

You will have to check your thermostat for this step. Confirm if the thermostat is in ON or not. A thermostat in ON means that air will continuously flow through the vents even if it is not cooling your home. It results in the AC blowing warm air. 

Fixing this is easy and requires the thermostat. Look for the switch with the FAN label. In most cases, it will have ON and AUTO modes. What you need to do is to switch the thermostat to AUTO mode. This way, air will only flow through the vents it is cooling.

Is your filter dirty?

When did you last clean your filters? If your AC is not cooling the house below 80°F, it may be because of a dirty filter.

AC filter

As air frequently passes through the filter, it can accumulate different elements such as dust. Cleaning your filters is important so that air can freely pass through.

Having a dirty filter will drastically reduce the airflow in your system, which causes it to struggle when cooling.

Remove the filter and check if it is dirty. If it is not, you need to clean it or replace it with a new filter. Some models have reusable filters, while others do not.

You need to check which type of filter it has with your make and model. It is advisable to check the filter once every two weeks.

rooftop air conditioning units

A clean filter does not only improves airflow to the system. It also contributes to the unit’s efficiency. A clean filter will have less strain on the AC system to pull air. Consequently, it will require less energy to do the work.

Here’s a quick overview of which filter to get:

  • Someone in your household has allergies or asthma: A HEPA filter. They’re great and can remove up to 99.97% of airborne particles.
  • Pets in the house: Use a filter with a higher MERV rating. These filters can effectively capture pet hair.
  • Are with high levels of pollution or household smokers: Buy a carbon filter. They’re great at removin odors and chemicals from the air.
  • Concerned about energy efficiency: A filter with a lower MERV rating. These will restrict airflow less.
  • You use a heat pump: Use a filter with a MERV rating between 8 and 13. They provide good protection but don’t restrict airflow too much.

Is the outdoor part dirty?

Other than the filter, the outdoor unit often gets dirty too. The outdoor part is also known as the condenser. It brings the heat outside the house. If the condenser gets dirty or covered with debris, the heat will have a hard time passing through it.

ac floor register

Cleaning it is typically a simple task to do. Looking at it, remove large debris such as leaves by hand. Once done, get a garden hose and gently clean the fins. It is important to note that the water pressure coming off the hose should be gentle. It may damage the condenser fins, which will affect airflow.

Speaking of leaves clogging the system, it is important to plant trees and grow plants such as the hibiscus tree and the tomato plant.

Has the circuit breaker tripped?

A lot of units have two circuit breakers. One circuit breaker is for the indoor part, while the other is for the outdoor part. There are cases when the circuit breaker for the outdoor unit trips, but the indoor circuit breaker does not. It will continue running, but the air flowing through will be warm. 

circuit breakers

To fix this, you will need to check the breaker box for the outdoor unit. If the breaker tripped, you need to switch it on. Turn on your unit and observe. If the breaker trips again, do not attempt to switch it on. It is a sign that there is a bigger issue.

Suppose you’ve set up a unit in a part of the house without electrical outlets. You may also want an extension cord that comes in different lengths to keep your house at the right temperature. It’s no different from buying a cassette toilet or a garden tractor. You want to make sure you’re getting the right one. 

Why is it running but not lowering the temperature?

air conditioning unit

It is common to think that lowering the thermostat will give more cooling. Lowering the temperature only means the AC will run longer to meet the temperature in the thermostat.

There are a few possible reasons why your AC is not lowering the temperature. The first is clogged filters. Check the filters and ensure that the filters are free from debris and other external elements. 

new replacement AC filter

It is also possible that something is blocking the condenser. Remember that the condenser needs to be clear from obstruction because it gets rid of heat.

Blocking the condenser will only make it difficult for the heat to exit. As a result, your unit cannot meet the low-temperature setting of the thermostat.

There are also cases when the thermostat is not working fine. A miscalibration in the thermostat may force the AC to turn off without even reaching the desired temperature.

When it comes to the thermostat, you will need professional help to fix it as it involves a lot of electrical work.

central AC unit

Lastly, loss of refrigerant may also be a possible reason why it is not lowering its temperature. Having refrigerant below the normal level will result in a loss in the cooling capacity.

To put it in simpler terms, the AC is running but not cooling enough. A refrigerant leak is a serious problem, which means you should call for professional help as soon as possible.

How long should it take to cool a house from 80 to 72?

There are a few things to consider when talking about how long it will take to cool an entire house. Factors such as the outdoor and the indoor temperature need consideration.

It will need a longer time to cool a house on a hot day. Typically, it takes four to six hours to cool a house from 80°F to 72°F.

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