AC Won’t Cool Below 75 Degrees

It can be frustrating to discover that your ac won’t cool below 75 degrees on a hot day. There are a few reasons your ac is not lowering temperature below 75, these include:

  • Outdoor temperature is 92 degrees or above
  • You air filters are dirty
  • Bad thermostat wiring
  • Your ac is running out of the refrigerant
  • Outdoor compressor unit is blocked
  • Your have an undersized air conditioner
AC not cooling below 75
A mini split ductless ac system

The above things are the common reasons you air conditioner is not cooling below your set temperature. However, when you notice that your ac is not cooling enough, you first need to check your thermostat settings. Verify that your thermostat is set to cooling mode and not heating mode.

Read also: AC Won’t Cool Below 74 Degrees [Solved]

On top of that, ensure that the temperature point is correctly set.

Reasons Your AC Won’t Cool Below 75 Degrees

While you can fix most of the issues that prevent your ac from cooling properly, others can be a bit complicated and will need the help of an HVAC professional. Let’s now jump right into details.

1) Hight Outdoor Temperature (above 92)

High outdoor temperatures (usually above 92 degrees) prevent your ac from working and cooling properly. Air conditioners are designed to work properly below 92 degrees. Besides that, an Air conditioner system is designed to cool your home just 20 degrees from your outdoor temperature.

In simple math, when your outside temperature is 95 degrees, you should expect your ac to cool your home to only about 75 degrees. High outdoor temperatures could explain why your ac is not cooling your home enough.


If you are experiencing high outdoor temperatures and if this is affecting your ACs cooling, there’s little you can do to control the outdoor temperature.

However, you can prevent the hot outdoor air from getting into your home by closing doors and windows. To help improve cooling for yourself, you can try turning on fans (ceiling or any other fan).

At night, the outdoor temperature becomes moderate, so you should not have problems with your air conditioner cooling.

2) Dirty Or Clogged Air Filters

A dirty air filter could be the reason why your ac is not cooling your home below 75 degrees. If your outdoor temperature is below 92 degrees but your air conditioner is not cooling properly, check your filter.

Clogged air filter
A woman looking at a clogged air filter

Air filters help to trap dirt and other unwanted things from air before it gets to your evaporator coil. 

However, when your filters are clogged, they will reduce the amount of air that gets into your ac system. Because of that, only a fraction of air will be cooled and circulated into your home. This significantly reduces the efficiency of your ac system.

Also read: Heat Pump Not Cooling Below 80 Degrees [Solved]

The fix?

Because air filters trap dirt, they can quickly become clogged. That is why you need to replace or change air filters in 1-2 months. You need to regularly check the status of your filter.

New air conditioners have filter check lights that remind you when the filter is due for change or cleaning. But for older HVAC system, you’ll need to manually keep track of the time your filter has been running before a replacement.

How do I change my AC air filter?

Air filters are easy to change. You can find your air filter at the return vents or at the air handler unit in your home.

Once you locate it, take it out and look at it? Does it look like the color of mud?  If so, then you need to get another one.

Take note of the model number or the size of the filter before getting another one.

PS: When installing a new filter, ensure the arrow on it points into the correct direction. Typically, away from the door. And don’t run your ac without the filter, this can cause more issues with the entire ac system.

3) Bad Thermostat Wiring

A bad thermostat wiring causes many different ac problems. Depending on the type of the thermostat you have. You might want to check if the wiring is in order.

If you recently changed or upgraded your thermostat, bad wiring could be causing your ac cooling problems.

Remove your thermostat from the wall and recheck the wiring. If necessary, get your user manual for instructions. Alternatively, or probably a better option, check the wiring designation in your HVAC control panel compartment for your wiring reference.

4) Leaking Out Refrigerant

If your refrigerant is leaking out of your ac system, your ac will not cool your home. The refrigerant is a special chemical used in the ac system that transfers heat between two environments by way or condensing and evaporating.

With age, your system can become vulnerable to leaks or damage on some parts. When there are leaks, your refrigerant can escape.

What to do when your ac is running out of the refrigerant.

Usually when your system is running out of the refrigerant, you’ll experience cooling problems and other times, the compressor will just shut off.

Recharging AC with a refrigerant
A man recharging and ac with a refrigerant

But when this problem occurs, there is nothing much you can do but call professionals to come and assess the problem. Professionals typically use special tools to investigate the leaks and seal them off.

They will also test your system if the problem has been rectified before recharging it with any more refrigerant.

Read Also: Nest Thermostat Blowing Hot Air on Cool [Solved]

5) Blocked Outdoor Condenser Unit

A blocked condenser unit will not be able to release heat to the outdoor air. This in turn will prevent the air conditioner from lowering the temperature to your set point. To avoid this problem, always ensure that there no objects covering your condenser unit.

If you see dirt on it, clean it away. A hose is a good tool to help you clean away the dirt from your condenser by way of spraying water on the condenser unit.

clogged condenser coil
A dirty condenser coil

Cut off any outgrown shrubs and blow away nearby leaves. Leaves and debris are among the things that can easily clog your condenser coil and fins.

6) Undersized Air conditioner

An undersized air conditioner is another possible reason your ac is not lowering temperature enough. Did you have any home modification/extension project?

If your home was extended, your air conditioner has probably become too small for your home.

An air conditioner’s power for cooling is measured in BTUs. Usually before your air conditioner is installed, you need to measure the size of your home or room space and that will give you the size of the air conditioner that will be needed to do the job.

But if you miscalculate or do not take into consideration the sizes, you might run into cooling problems. On the other hand, an oversized air conditioner can also cause problems.

The Fix?

If you have an undersized ac unit, the best option is to replace it with the right sized one. While this is not an option for every homeowner, there are a few things you can do to improve cooling when you have an undersized air conditioner. They include:

  • Closing outside doors and windows to prevent outdoor air from sneaking in. Seal off gaps between air windows, walls and the air conditioner.
  • Turning off some heat producing appliances when not in use. Instead of using the stove, you can try grilling outside.
  • Avoid doing laundry when your ac is on.

If these 3 tips don’t work for you, consider getting a new correct sized ac unit.

Read also; Heat Pump Not Blowing Cold Air [Solved]


Is it OK for AC to run all day?

Yes, it is generally fine for your air conditioner system to run all day. But there are a few things you need to consider when running your ac.  These include

  1. Energy Saving: If your ac is running through out the day, it will consume more energy. And if there are other people in your neighbourhood running their air conditioners all the time, the systems can put pressure on the power grid. Sometimes this can trigger a power outage.
  2. High Electricity Bills: If your air conditioner is running throughout the day, you expect high electricity Bills.
  3. You’ll need to replace air filters more often. Typically, replacement of air filters depends on the number of hours your ac has been running. If you run your ac more often, you need to change your filters frequently.

TIP: You can run your ac all day and ensure energy saving by setting your thermostat to a moderate point to allow your ac to take breaks.

How cool should my house be if it’s 90 outside?

If your house is 90 degrees outside, you should expect your house to cool down to about 70 degrees if it is working efficiently. By working efficiently, I mean your ac should have clean air filters and your condenser unit should not by covered or blocked by objects.

Air conditioners are designed to cool indoor temperatures by 20 degrees from the outside temperatures. Its also worth noting that an air conditioner is designed to work properly and efficiently if the outside temperature is below 92 degrees.

Final Thought

Well, if your ac won’t cool below 75 degrees, try out the above tips in this guide to help you find a solution. If the problem is not solved, then try calling local HVAC maintenance and repair services. They should be able to troubleshoot and solve this problem quickly. Thanks for reading.

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