Air Conditioner Running But Not Cooling [Solved]

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If you are dealing with an air conditioner that is not blowing cold air but running, then this article will be helpful for you. And if you ask yourself, ‘why is my ac not blowing cold air?’ A few things can prevent your air conditioner from blowing cold air. These include:

  • Dead capacitor
  • Thermostat issues
  • Bad condenser fan
  • Low refrigerant
  • Dirty air filters
  • Dirty or blocked return duct
  • Blocked condenser coil
  • Dirty evaporator coil
  • Leaks in the ductwork
  • Undersized air conditioner
  • Open doors and windows

So in this AC troubleshooting guide, I’ll discuss these 13 reasons why an AC will be running but not blowing cold air, along with some quick suggestions on how you may be able to fix it yourself before having to call on the experts.

Also read: Air Conditioner Outside Unit Fan Not Working

an air conditioner not blowing cold air but running
A typical air conditioner outdoor unit set up

How Does a Home AC or Heat Pump System Work?

An air conditioner and a heat pump system work on the same basic principle your home refrigerator runs. They all use a chemical known as refrigerant. Nearly all modern cooling systems use halogenated chlorofluorocarbons (HCFCs) as the refrigerant. I don’t want to go into details here, but you can find useful resources here.

An AC system typically has an indoor unit and an outdoor unit. The indoor unit comprises of a coil called an evaporator and an outdoor unit has a condenser coil.

So, this is how your AC system should work to cool a house:

  • The pump (compressor) pushes the freon through a network of coils. The liquid refrigerant evaporates in the evaporator coil as warm indoor air comes in contact with the coil.
  • As the refrigerant evaporates into a gas and goes into the condenser coils, it carries heat from the indoor air.
  • This heat is transferred to the outdoor air as the refrigerant condenses to liquid. That’s why it’s important not to have any objects covering your outdoor unit.
  • The cycle continues until the set temp point is reached.

That is basically how your central ac system works when running properly. Now let’s dive into details of common issues that can negatively affect the normal working of pushing cool air through your cooling system.

The 13 Main Reasons For Your Air Conditioner Running But Not Cooling (Check These Before Calling a Professional)

There are a variety of issues that can prevent your air conditioner from working properly. Below are the most common reasons for your AC is running but not blowing cold air in your home.

1) Dead Capacitor

A dead capacitor will prevent your air conditioner from blowing cold air. Most air conditioners come with dual capacitors for powering your compressor and fan motor. However, with time any part of a capacitor can malfunction and die. Check out how to test an AC dual capacitor.

If part of a capacitor that powers the compressor dies, the other part that powers the fan motor can continue running. The fan will be spinning, but your ac won’t blow any cold air because of a non-functioning compressor (shortly, I’ll briefly explain how a compressor helps with cooling your home). But if this seems to be your issue, you can get new capacitors online for pretty cheap. (Pro Tip: don’t buy a capacitor from the AC Fix it guys, they will charge you $150 or more where these things can be purchased for ~$20 in most cases.)

2) Thermostat Issues

When you notice that your air conditioner is not cooling despite turning it on, you need to check your thermostat. Thermostat issues that could negatively affect your air conditioner’s cooling include incorrect thermostat settings and bad thermostat wiring. This is different from a portable AC that is not cooling. So let’s jump right into how each of these issues can affect how your ac works.

a) Thermostat settings

Incorrect thermostat settings can prevent your air conditioner from cooling your home even when your ac is running. Ensure your thermostat is set to ‘cool’ and the cooling point is below the room temperature reading.

To check if cooling is working, adjust the thermostat cooling point to the lowest and wait for a few minutes to see if cool air will start flowing.  Setting your thermostat to the lowest point doesn’t necessarily mean your ac will become cooler but means that your ac will have extended time in the cooling cycle.

You can even go to the vents. Make sure they are not closed or blocked by objects. Open any closed registers and vents and put your hand over to feel if any cool air is coming.

If no cool air comes out of your vents, and you have set your thermostat to cool, find out if the outdoor unit is working. You can check if the condenser fan is spinning or the compressor is working. If the outdoor unit usually runs, your thermostat wiring could be the problem.

b) Thermostat wiring

Bad thermostat wiring could be why your air conditioner is running but not cooling your home. 

Did you recently install a thermostat by yourself? If so, open your thermostat and check that every connection was made correctly. You can also find the reference for wiring designation in the compartment for the circuit control board of your HVAC system.

Check the wiring designation and make sure everything is firmly connected. Don’t leave any loose wires. If you are troubleshooting a Honeywell thermostat, you may find this article useful. You can call your thermostat’s manufacturer support for further assistance for all other brands.

To check the status of your thermostat wiring, remove it from the wall. For some thermostats, you might need a screwdriver to do this. Make sure that the following terminals are connected:

S – Indoor and Outdoor Wired Sensors

Y – Compressor Stage 1 (Cooling)

Y2 – Compressor Stage 2 (Cooling)

G – Fan

C – Common

3) Your AC System May Need a Reset

If the circuit control board of your air conditioner is not responding to cooling adjustments on your thermostat, your ac system may need a reset to get your control board to respond. How to reset your air conditioner depends on the model of your air conditioner.

But the universal method of resetting any air conditioner is by tripping the breaker for a few minutes before flipping it back. This should reset your air conditioner. For resetting any specific model, refer to your user manual with specific instructions.

Also read: Home AC Not Blowing Cold Air

4) Leaking or Low Refrigerant

A leaking refrigerant is among the most common reasons an air conditioning system is not cooling.

Air conditioners use refrigerant to cool your indoor air. Without it, your air conditioner can never cool your home. Let’s briefly look at how the refrigerant brings about cooling in your home.

  • Your ac indoor unit houses the evaporator coil, and your outdoor unit has a condenser coil. The refrigerant runs through a network of coils between the evaporator coil and the condenser coil.
  • While passing through the evaporator coil, the refrigerant will absorb heat from the indoor air that passes over the evaporator coil. The heat from indoor air will be transferred to the refrigerant, and the refrigerator turns into gas.
  • Then this gaseous refrigerant will go to the compressor, which will be pressurized and sent over to the condenser coil. At the condenser coil, the gaseous refrigerant will dispose of heat and condense it into liquid. From here, the cycle continues until the temperature in your home falls below the set point.

How will a leaking refrigerant cause no cooling in your home?

Now that we have looked at how a refrigerant is used to cool your home. It will be easy to understand how a leaking refrigerant will prevent cooling in your home.

When refrigerant is leaking from your air conditioner system, you won’t have any cooling in your home because there won’t be heat transfer between the indoor and outdoor air.

The solution to a leaking refrigerant

If you believe you have a leaking refrigerant, turn off your air conditioner to prevent your compressor and other components from being damaged. Then call a local HVAC professional to come and assess the problem. HVAC professionals will be able to pinpoint the leaks using their special tools. They can also recharge your air conditioner with a refrigerant if necessary.

So, when you have a low charge of the refrigerant in your system, that is a good sign that there are leaks within the system.

5) Leaks Or Disconnections in the Ductwork

 Leaks in the ductwork can prevent your air conditioner from blowing cold air when running. Air ducts are installed in areas with temperatures that are not controlled (in the attic). Variations in temperatures between seasons coupled with old age could cause ductwork to develop disconnections between them.

And if you are unlucky, rodents find their home in your attic could cause considerable damage to the ductwork. They could chew the air ducts and create leaks. As cold air passes through your ductwork that has leaks, there could be a mix of air in the attic and air in the ductwork. In short cold air could escape before reaching your leaving spaces.

Try inspecting your ductwork for problems. Usually, you can fix most of these issues without the help of professionals. You may use new pieces of your ductwork to repair disconnections. Alternatively, you may use metallic tape to seal off the leaks.

If you can’t find the leaks, a call to a professional HVAC technician is in order.

6) Blocked Condenser

A clear landscape around a condenser
A clear landscape around a condenser

Your air conditioner’s outdoor unit has condenser coils, a compressor, and a condenser fan. The condenser fan draws air into the condenser coils and takes the heat from your home to the outside air.

When foliage is near the condenser unit, your coils could quickly become dirty and covered with leaves and debris. This will prevent your condenser coils from disposing of the heat to the outside air. Thus, this will make your air conditioner’s cooling inefficient.

A blocked condenser unit can easily be cleaned by using a hose to rinse it. You can also clear areas around the condenser unit to prevent debris from accumulating around the condenser unit.

7) Dirty Condenser Coil

When your condenser unit has too much dirt, debris, and other objects blocking it, it can prevent your air conditioner from blowing cold air. The condenser unit sucks air from the sides, passing it over the coils and rejecting it up. So, the air that comes in and out removes heat from the condenser unit.

Dirty air condenser
A condenser unit that is dirty and clogged

 When the condenser unit and the condenser coil get dirty, it is very dirty; they will restrict the flow of air, and heat won’t be transferred to the outdoor air. You can clean the condenser unit by spraying water. You can use the hose water to cleanse it.

8) Dirty Evaporator Coil

A dirty evaporator coil will reduce the amount of heat absorbed from your indoor air. Dirt and other substances plugged into your evaporator will decrease the surface area of the evaporator that absorbs heat.

 While dirty air filters are a common cause of a dirty evaporator coil, this can also happen when you forget to put your air filter in.

The last thing you want is your coils getting dirty. Dirty coils are hard to clean; you will need to call HVAC professionals to come and help you clean them.

9) Dirty Air Filters

Dirty air filters will restrict the airflow around the evaporator coil, which will affect your home’s cooling. Air filters work all the time when your air conditioner is running. They catch dirt, dust, and other substances and prevent them from getting to your evaporator coil.

Clogged air filters will also block the passage of air, and because of this, air can bypass your filters and find its way into your ac unit. And this is what will happen:

  • Air that bypasses your filters will deposit dirt on the evaporator coils. When the coils are covered with dirt and other objects, this will reduce their heat-absorbing capabilities, and this will prevent your indoor air from being cooled as expected.
  • Your air conditioner will overwork to cool your home, resulting in more electricity bills.

To prevent this from happening, always remember to change filters at least once in 2 months or as recommended by your manufacturer.

10) Undersized AC System

 If your air conditioner system is way too small for your home, it will be underperforming, and you’ll feel like your ac is not blowing cold air. Some ACs installations are done without properly calculating the size of the home and the air conditioner that can fit. If you believe your air conditioner is too small for your home, there are still a few things you can do to help with cooling. So, you can try:

  • Insulating your home where there is no proper insulation.  
  • You can also try using a sealant to seal gaps between windows and doors.

Alternatively, you can use online tools for air conditioner/room sizing.

11) Some Windows Are Open Inside Your House

If your windows and doors are open, your air conditioner will not cool your home the way you expect. Some people think that open windows can not affect the efficiency of your air conditioner, but this is not true.

When windows are open, warmer air will always come and displace the cooler air blown out of your air conditioner. Because of that, you will not feel the cool air coming out of your vents.

It’s always best to close windows and doors and seal off gaps where necessary; this is where warmer air could be passing t to get into your home.

12) Tripped Breakers

Another possible reason your AC is not blowing cold air is a blown-out fuse or a tripped circuit breaker. Usually, a heat pump has separate breakers for indoor and outdoor units.

Most likely, the outdoor unit will trip the breaker, and while the power to the condenser unit will cut off, your indoor fan can keep blowing air that is not cool.

Head over to inspect the circuit breakers and, if possible, look at the power switches for both the indoor and the outdoor unit.

The power switch for the indoor unit is typically installed near the door, while the outdoor unit is near the area where refrigerant lines get into your home.

If any switch is off, switch it on and observe if your air conditioner will start blowing cold air.

13) Malfunctioning Reverse Valve

Issues with the reverse valve could cause the heat pump not to cool.  The reverse valve is a component of your heat pump system responsible for switching the refrigerant flow so that your heat pump can work as a heater and an air conditioner.

After years of use, the reverse valve can malfunction and get stuck in heating or cooling mode.

If the problem is with your reverse valve, try running your heat pump in the heat mode. If it works fine in heat mode but does not work in cool mode. Then the reverse valve could be the culprit. In this case, it is wise to call in HVAC repair services.

How To Prevent Unforeseen AC Problems

Regular maintenance should be done on your air conditioning system to avoid unforeseen breakdowns. Generally, it’s a good practice to have HVAC tune-ups at least twice a year.

Air filters can work for about 2 months because they can be changed. Regular maintenance will keep your central AC system working efficiently.

If you hear any strange noises coming from your air conditioning system, do not ignore them; try to find out where the noises are coming from.

Same with smells, unusual smells from your HVAC system could mean a problem. Never ignore these signs. If they go without being checked, other HVAC system components could be worn out. Eventually, this can result in unforeseen and costly breakdowns.

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Final Thought

Having looked at the possible reasons for your air conditioner running but not cooling, the next time you are dealing with this issue, try going through our tips before calling in HVAC professionals. You might just save yourself that service call.

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