Air Conditioner Not Cooling House Below 80 (10-Step Fixing!)

It’s typical to want to cool your house below 800F during the summer by seamlessly adjusting the air conditioner. But is your air conditioner not cooling house below 80, and you don’t know why?

Your air conditioner won’t cool your house below 800F because it’s undersized or aged or due to issues like a tripped breaker, clogged air filter or coils, blocked condenser, or leaky ducts. Other issues include a clogged drain, dead thermostat batteries, faulty thermostat, or low refrigerant.

One of these ten reasons is why you cannot enjoy a cool in-house temperature during the summer. Fortunately, you can troubleshoot those issues yourself, and I will show you just how.

We will discuss each problem concerning how it prevents your air conditioner from lowering the temperature below 800F and what to do to remedy it. 

Some issues may require an expert’s help, but most are DIY. So, before you can run to an HVAC pro for help, it may save time and money to consider the issues.

Let’s jump into it!

air conditioner not cooling house below 80

In a hurry? Below are the recommended fixes to the 11 issues that can stop a home air conditioner from lowering the indoor temperature below 80 degrees. 

Quick Troubleshooting Guide for an Air Conditioner Not Cooling House Below 80

Likely Cause Recommended Fix 
1.Undersized UnitReplace the air conditioner with a higher capacity (or BTU) option if it’s smaller (capacity-wise)
2.Aged UnitGet a new air conditioner if the current one is older than ten years
3.Clogged Air Filter Replace the air filter if you’ve been using it for over 30 days 
4.Clogged Coils Thoroughly clean the condenser and evaporator coils if they are filthy
5.Blocked Condenser Clear any obstructions around the condenser, especially shrubs, branches, dense fences, and dirt heaps 
6.Leaky Ducts Use duct tape, mastic, or paintbrush to seal up any leaky ducts
7.Clogged Drain Clean the drain line from any clogging or hire an expert 
8.Dead Thermostat Batteries Replace the thermostat batteries if they are older than one year 
9.Faulty Thermostat Replace the thermostat if its reading and that of the thermometer varies 
10.Low Refrigerant Call an HVAC pro 

How to Fix an Air Conditioner Not Cooling Below 80 Degrees? 

Generally, your air conditioner won’t cool your house below 80 degrees because of one of these ten issues:

  • Unit under-sizing (the AC having a smaller capacity than what the room needs)
  • Aged unit (an air conditioner that’s older than ten years)
  • A dirty air filter 
  • Dirt-clogged condenser or evaporator coils 
  • Suffocating condenser 
  • Leaky air ducts 
  • Clogged drain line 
  • Low-power thermostat batteries 
  • Defective thermostat 
  • Refrigerant leakage 

Now that you know what to check, let’s go through them in the proper order. Below are the ten steps for fixing your house AC when you can’t lower the temperature below 80 degrees or even below 75 degrees.

Step 1 – Check if the air conditioner is undersized

The air conditioner will struggle to cool your house if its capacity (what we know as the BTU rating) is smaller than what the room needs. Yes, the air conditioner might run, but it may not cool your space enough, and you don’t want that. 

What to do:

It’s essential to check if the air conditioner is the right size, and here’s a table to use. 

Room Size (Maximum Square Footage)AC BTU or Capacity
150 5,000 sq.ft 
250 6,000 sq.ft 
300 7,000 sq.ft 
350 8,000 sq.ft 
400 9,000 sq.ft 
450 10,000 sq.ft 
550 12,000 sq.ft
700 14,000 sq.ft 
1,000 18,000 sq.ft 
1,200 21,000 sq.ft
1,400 23,000 sq.ft 
1,500 24,000 sq.ft

If the AC does not match the room (if it’s too small), consider replacing it with a bigger capacity AC. Note, however, that you need to increase the AC capacity by about 10% if your room is extra sunny and reduce it by 10% if it’s heavily shaded.

And if the AC serves the kitchen, which is obviously hotter than the other rooms, improve the BTU rating by 4,000. 

Step 2 – Consider that the air conditioner might be too old

Sometimes the air conditioner might be the right size but fail to cool correctly because it’s too old to do so.

Ideally, air conditioners are at their peak in under ten years. Once they hit a decade, they reduce performance and are more likely to break down, thus being unable to cool your house properly. 

What to do: 

Get a new air conditioner if the existing is older than ten years. Remember that a newer AC will cool your house correctly and save you about 10% of the house cooling cost. 

Ac not cooling house

Step 3 – Inspect the air filter for clogging 

The air filter’s job is to catch contaminants before they can enter the air conditioning system. Over time, the filter clogs with the impurity it traps, thus restricting airflow. 

That means your air conditioner suffocates, and when it does so, it’s unable to cool your house correctly. And even if it starts to cool, it may turn itself off.

That’s the main reason you should replace the air filter monthly. It should be one of the first to check when the AC won’t cool enough. 

What to do:

If your air filter is dirt-clogged or perhaps older than one month, change it. It’s highly likely the reason behind the AC’s cooling issues. 

Step 4 – Inspect the condenser/evaporator coils for clogging

The air filter is not the only thing that can reduce the AC’s cooling effectiveness when it becomes dirt-clogged. The condenser and evaporator coils have the same effect. 

They make it harder for the AC to pass hot air outside. As a result, the room will likely get hotter even if you try lowering the AC’s temperature.

What to do:

Consider cleaning the coils and their surroundings to eliminate dust and dirt. If you cannot, have an expert HVAC technician help you.

Step 5 – Unblock the condenser unit 

The next stop is the condenser. This outdoor unit should breathe properly. If obstructions such as debris heaps, shrubs, branches, and dense fences are around it, the condenser cannot collect indoor heat and pass it outside. 

So, in the end, your house becomes warmer, and the AC cannot lower its temperature below 80. 

What to do: 

Inspect the condensers surrounding to clear any possible obstructions. Ensure there are no dirt heaps, shrubs, branches, and dense fences close by as they may suffocate it. 

Step 6 – Seal up any leaky duct

Cold air could be escaping the air ducts, and if so, that’s the reason the air conditioner won’t lower the temperature beyond a certain point. 

So, it makes sense to carefully inspect the air ductwork for any openings that might be leaking cold air. 

What to do: 

If there are any sources of air leaks on the ductwork, seal them. Here are the signs your air ducts are leaky:

  • The air conditioner won’t cool or heat, and if it does, the cooling/heating is uneven
  • Some rooms have more dust than others 
  • AC makes a whooshing or whistling sound when escaping the duct 
  • Higher energy cost 

Remember, the air will likely leak along the joints/elbows and where there are old tapes. You can fix the leaky ductwork yourself using duct tape (a temporary fix) or mastic and paintbrush (a more permanent fix).

If the job is too technical, call an HVAC professional.

Air conditioner running but not lowering temperature

Step 7 – Unclog the drain line (if blocked)

If there’s a clog along the drain line, it will force the float to shut down the compressor. Once the compressor stops running, the air conditioner quits cooling. So, this could be the reason the AC won’t drop your house temperature below 80 degrees. 

What to do: 

Inspect the AC’s drain line for possible clogging and clean it. Consider talking to an HVAC pro if you cannot do it or lack the right tools for the job. 

Step 8 – Replace the thermostat batteries 

Though a minor issue, sometimes the thermostat batteries could be why your air conditioner won’t cool below 80. That’s if the batteries are weak, which is likely to be the case if older than one year. 

What to do: 

Consider changing the thermostat batteries if you’ve been using them for more than one year. 

Step 9 – Replace the thermostat 

Sometimes the problem is not the thermostat batteries but the thermostat itself. If it’s faulty, it won’t communicate the correct information to the air conditioner, preventing it from cooling properly. 

What to do: 

Use a thermometer to check if the thermostat is working. Just tape the two together for about 15 minutes and examine their readings. If the readings are different, recalibrate the thermostat and repeat the test.

If you still get different readings after that, replace the thermostat. 

Step 10 – Check for possible refrigerant leakage 

Lastly, consider that the liquid coolant (or refrigerant) might leak, thus not sufficiently absorbing the indoor heat.

Overall, here are the signs that the refrigerant is leaking:

  • Iced-up evaporator coils 
  • Higher home energy costs
  • Frozen refrigerant lines 
  • Whistling or hissing sounds along the refrigerant lines 
  • The air conditioner not cooling or taking forever to do it

What to do:

Consider contacting an HVAC professional when you notice any of the above signs. An HVAC professional will identify the source of the refrigerant leak and correct it. 

Why is my air conditioner running but not cooling the house

Air Conditioner Running But Not Lowering Temperature (Not Cooling House Below 80)

If your air conditioner is running but not lowering the house temperature, the problem could be the thermostat which is set wrongly (not on COOL mode) or faulty or the AC itself which is too old (more than ten years) or undersized.

Other issues include leaky ducts, dirty air filters, frozen coils, or low refrigerant.

People Also Ask 

1. Why Is My Ac Not Cooling House?

Your AC might not be cooling your house for different reasons. It could be because the AC is too small (in capacity) or older (more than ten years). It could also be due to leaky ductwork, filthy air filter or coils, refrigerant leakage, or blocked condenser.  

2. Why Does My AC Not Go Below 80? 

Your AC doesn’t go below 80 degrees because it’s too old (older than ten years) or low capacity (lower BTU). If not, it could be due to dirty air filters or coils, a refrigerant leak, an obstructed condenser, or a faulty thermostat. (  

Closing Thought On Air Conditioner Not Cooling House Below 80:

In conclusion, your air conditioner won’t cool your house below 80 degrees because of different issues. The most likely ones are an undersized or old unit, clogged air filter or coils, suffocating condenser, leaky ductwork, clogged drains, low power thermostat batteries, malfunctioning thermostat, or refrigerant leakage. 

So, it’s all about identifying which of the ten issues relate to your AC and fixing it. 

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