Depending on location and preference, the ideal air conditioner’s room temperature is about 68 – 75 degrees Fahrenheit (OF). Sometimes, however, the air conditioner won’t cool below 75, and you’ve to ask why.
Your air conditioner won’t go below 75 OF because of the wrong sizing, higher outdoor temperature (above 95 OF), a dirty air filter, a tripped breaker, leaky ductwork, a blocked outdoor unit, faulty thermostat wiring, exhausted thermostat batteries, or refrigerator leakage.
It could also be due to a clogged condensate line, iced-up evaporator coils, a defective compressor, or an older AC.
Indeed, something must be wrong when your air conditioner won’t cool enough, significantly when it doesn’t drop below 75 degrees.
I’ll explain all those issues and their fixes to enable you to get your AC back cooling seamlessly.
Let’s jump into it!
In a rush? See the table below for quick fixes to the various issues that could prevent your air conditioner from cooling below 75 degrees.
My Air Conditioner Won’t Go Below 75 – Quick Troubleshooting Guide
| Likely Cause | Quick Fix | |
| 1. | Wrong AC Sizing | Upgrade to the right AC size |
| 2. | Higher Outdoor Temperature (Above 95) | Open the window and doors or use a cooling fan to supplement the AC |
| 3. | Dirty Air Filter | Replace the air filter if it’s dirty (do it after 1-2 months) |
| 4. | Tripped Breaker | Reset the breaker |
| 5. | Leaky Ductworks | Seal the leaky spots on the ductwork |
| 6. | Blocked Outdoor Unit | Remove any obstructions (debris, branches, shrubs, furniture, etcetera) around the condenser |
| 7. | Faulty Thermostat Wiring | Have an HVAC pro check and fix the thermostat wiring |
| 8. | Exhausted Thermostat Batteries | Replace the thermostat’s batteries |
| 9. | Refrigerant Leakage | Contact an HVAC expert to fix the source of the refrigerant leakage and refill the refrigerant |
| 10. | Clogged Condensate Line | Call an HVAC pro to unclog the condensate line if you can’t do it |
| 11. | Iced-Up Evaporator Coils | Change the air filter but if that doesn’t work, call an HVAC expert |
| 12. | Faulty Compressor | Contact an HVAC pro to check the compressor |
| 13. | Older Air Conditioner | Replace the air conditioner if it’s older than 10-15 years |
Why Your Air Conditioner Won’t Cool Below 75 Degrees
Your air conditioner won’t go below 75 degrees for different reasons. The most common ones are shared below:
1. New Air Conditioner Won’t Cool Below 75 Because It’s the Wrong Size
If your air conditioner is newly-installed or newly bought but cannot cool below 75 degrees, it’s likely the wrong size, mainly undersized. Such an AC won’t allow you to lower the thermostat temperature past a specific limit, in this case, below 75 degrees.
Fix
Matching your room size with the correct air conditioner capacity (or BTU rating) is essential. If the unit is undersized, it won’t cool your room, and if it’s oversized, it won’t be able to remove all the humidity, thus risking mold growth.
Below is an air conditioner sizing guide you can use on most window-mounted and portable home air conditioners:
| Maximum Cooled Area | AC Capacity |
| 150 SQFT | 5,000 BTU |
| 250 SQFT | 6,000 BTU |
| 300 SQFT | 7,000 BTU |
| 350 SQFT | 8,000 BTU |
| 400 SQFT | 9,000 BTU |
| 450 SQFT | 10,000 BTU |
| 550 SQFT | 12,000 BTU |
| 700 SQFT | 14,000 BTU |
| 1,000 SQFT | 18,000 BTU |
| 1,200 SQFT | 21,000 BTU |
| 1,400 SQFT | 23,000 BTU |
| 1,500 SQFT | 24,000 BTU |
2. Extremely Higher Outdoor Temperature
While your air conditioner may cool just fine when the outdoor temperature is below 92 degrees, it won’t do it properly if it is above 75. Essentially, the air conditioner cools by 20 degrees below the outdoor temperature.
So, if the outdoor temperature is 95 degrees, the AC will drop by 20 to 75 degrees, but if it’s 96 or higher, the cooling temperature will be above 75 degrees.
Fix
While there’s little to do since you don’t have power over the outdoor temperature, you can try lowering its effect indoors by shutting the windows and door. Additionally, you can use fans to supplement the AC.
3. Dirty Air Filter
Dirty air filters prevent the air conditioner from cooling correctly and may even cause it to turn off itself. That means the filter could be why your AC’s temperature won’t drop below 75 degrees.
When the air filter is dirt clogged, it reduces the amount of cold air flow and thus reduces cooling.
Fix
Change the air filter if it’s dirty. Most manufacturers recommend replacing the AC filter after 1 – 2 months, depending on usage.
4. Tripping Breaker
Sometimes it’s harder for the air conditioner to cool well when the circuit breaker keeps tripping. The circuit breaker may trip off if it’s loose or faulty. So, you may have to examine the unit’s circuit breaker to see if it’s off.
Fix
Examine the circuit breaker to reset it if it’s tripped. However, if it continues tripping, contact a local electrician.
5. The Air Conditioner Will Not Cool Below 75 Due to Leaky Ductwork
If the ductwork leaks cold air, it may be hard for the air conditioner to run at a very low temperature. For that reason, it’s imperative to seal any air leakage sources to keep the AC’s temperature within a specific limit.
Fix
Inspect the ductwork for any leaky spots and seal them. If you cannot do it, talk to an HVAC expert.
6. Blocked Outdoor Unit
The outdoor unit, especially the condenser, should have proper airflow. Nothing should block it from good airflow, including debris, branches, furniture, and shrubs.
You’ve to look at all these things to ensure that none of them are blocking the condenser from adequate airflow and remove it.
Fix
Cut loose branches and shabby shrubs from blocking the condenser unit and clear any dirt or debris heaps around it. Remove anything else, including outdoor furniture, that could obstruct the AC.
7. Faulty Thermostat Wiring
If there’s a wiring fault on your AC’s thermostat, it’ll be hard to set it correctly. The faulty wiring causes the thermostat to fail, making it harder for the air conditioner to cool appropriately.
Fix
If you can, take out the thermostat and examine its wiring against the design in the manual. If something looks amiss, contact an HVAC expert.
8. The Air Conditioner Thermostat Won’t Go Below 75 Due to Exhausted Batteries
The thermostat depends on its batteries to run. If the batteries are power-drained or exhausted, the thermostat won’t be able to run correctly. So, keeping the temperature below 75 degrees or any other lower range will be challenging.
Fix
Replace the thermostat batteries and then try out the thermostat to see if its temperature setting is adjustable.
9. Refrigerant Leakage
A drop in the refrigerant level affects the cooling performance of your air conditioner. A low refrigerant level means the AC cannot transfer warm heat from the inside to keep the indoor space cool.
Overall, issues like damage and wrong AC installation could cause the refrigerant to leak, and an expert can help you fix them.
Fix
A drop in the refrigerant level calls for a refill. Don’t, however, perform the refill as it requires an expert. So, contact an HVAC expert when you suspect a refrigerant leakage. Signs include an AC that won’t cool, wetness around the outdoor unit, and a smelly AC.
An HVAC export won’t just fix the source of the leakage but will also refill the refrigerant.
10. Clogged Condensate Line
Sometimes the condensate line accumulates too much dirt and debris, blocking it and deactivating the compressor. So, the compressor cannot run beyond a certain point, causing cooling loss.
Fix
Inspect the drain line for clogging and try unclogging it if you are handy and have the tools. But if you don’t, call an HVAC pro.
11. Iced-Up Evaporator Coils
Since the evaporator coils absorb the warm inside air before the refrigerant cools it (the air), it shouldn’t ice up. Some issues, however, such as a dirty air filter and refrigerant leakage, can cause the coils to ice up, thus making them unable to do their job.
Fix
Inspect the evaporator coils from icing over. If they are frozen, consider talking to an HVAC expert. Meanwhile, you can try to change the air filter.
12. Faulty Compressor
The source of the fault could be the compressor. If short-circuited, wrongly wired, or worn out, the compressor will restrict the air conditioner from cooling, as it won’t run well. Note that the compressor may also fail due to overheating or refrigerant leakage.
Fix
Since diagnosing a faulty compressor is difficult, it may be a good idea to contact an HVAC expert.
13. Older Air Conditioner
Lastly, the air conditioner might not be able to cool below 75 degrees because it’s too old. That might be the case if the AC is older than ten years. But overall, ACs have a 15-20-year lifespan.
Fix
Replace your air conditioner if you’ve been using it for more than 10 – 15 years.
People Also Ask
1. Why Is My AC Not Cooling Below 75 Degrees?
Your AC might not be cooling below 75 degrees because it’s too old (older than ten years) or undersized. Other issues worth checking are a dirty air filter, frozen evaporator coils, clogged drain line, faulty thermostat, tripping breaker, and low refrigerant.
2. Why Is My AC Not Cooling Below 77?
Your AC won’t cool below 77 degrees if the air filter is dirt-clogged, the evaporator coil is iced-up, or the refrigerant level is low. Also, check for possible leaky ductwork, a faulty thermostat, tripped breaker, exhaust thermostat batteries, or the wrong AC size.
3. Why Is My AC Not Cooling Below 74?
If your air conditioner won’t cool below 74 degrees, the issue could be that the AC is too small (undersized) or too old. It could also be that the air filter is dirty, the evaporator coils are frosted, or the condenser is obstructed.
Closing Thought When the Air Conditioner Won’t Cool Below 75:
As shared, your air conditioner won’t cool below 75 degrees for different reasons. The unit itself could be the wrong size (applying to a new AC) or too old.
But still, issues like a dirty filter, leaky ductwork, tripped breaker, blocked drain, obstructed condenser, low refrigerant, iced-up evaporator coils, and a faulty thermostat could be the problem. So, consider all 13.
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