An AC running but not cooling is one of the most common and frustrating mechanical failures a homeowner can face. When your system operates without lowering the indoor temperature, it wastes an enormous amount of energy while putting your expensive compressor at risk of a total burnout.
Therefore, you need to figure out exactly what is going wrong with your AC before a small glitch turns into an expensive system failure.
Let’s get started!
12 Common Reasons Why Your AC Is Running But Not Cooling
When your AC unit stays on but the temperature does not drop, it means the cooling cycle is broken somewhere along the line. Below, we have compiled this list of the most common issues we see in the field, along with the best ways to fix them.
1. Clogged and Filthy Air Filters
The air filter is the most common reason for airflow problems. When it gets dust and pet hair, it acts like a wall that prevents air from reaching your cooling coils. This suffocates the system and stops it from pulling heat out of your rooms, which is probably why your AC runs but not cooling properly.
- How to solve it: Check your filter once a month. If it looks gray or dusty, swap it out for a new one immediately to restore the airflow.
2. Incorrect Thermostat Settings
Sometimes the fix is as simple as a wrong setting. If your fan is set to “ON” instead of “AUTO,” the blower will run 24 hours a day, even when the cooling parts are resting. This circulates unconditioned air that feels warm and humid.
- How to solve it: Flip your thermostat fan setting to “AUTO”, so it only blows when the system is actively cooling the air.
3. Frozen Evaporator Coils
Your indoor coils need a steady stream of warm air to work right. If that air is blocked or your refrigerant is low, the coils get too cold and turn into a block of ice. Once they are frozen, they can no longer absorb heat from your home, often leaving the AC unit running but not cooling at all.
- How to solve it: Turn the system off and run the “FAN ONLY” mode to let the ice melt. Replace your filter and check for blocked vents before turning the cooling back on.
4. Dirty Outdoor Condenser Unit
The big box outside needs to release heat to the outdoors. In South Florida, these units often get covered in salt air grime, grass clippings, and sand. If the coils are dirty, the heat stays trapped inside your home.
- How to solve it: Turn off the power and gently rinse the outdoor unit with a garden hose. Make sure there is at least two feet of clear space around the unit for proper breathing room.
5. Refrigerant Leaks and Low Levels
Refrigerant is the “blood” of your AC that carries heat away. Your system should never run low on this fluid unless there is a hole in the lines. Low levels mean the air coming out of your vents will never feel truly cold.
- How to solve it: Look for hissing sounds or ice on the copper lines. You must call a licensed technician to find the leak, seal it, and recharge the system to factory specs.
6. Blocked or Leaky Ductwork
Your ducts are the “highways” for cold air. If a duct has come loose in the attic or is clogged with debris, that expensive cold air is escaping into your crawlspace instead of your bedroom.
- How to solve it: Have a professional inspect your ductwork for gaps or tears. Sealing these leaks can instantly improve your home’s comfort and lower your energy bills.
7. Failing Capacitors
A capacitor is like a small battery that gives the motor the “kick” it needs to start. These parts often pop or wear out during hot Florida summers. If one fails, your fan might spin, but the compressor will stay dead.
- How to solve it: Since this involves high-voltage electricity, you should have a technician test and replace the bad capacitor to get the system running safely again.
8. Faulty Compressor
The compressor in an AC is responsible for pumping refrigerant through the system. If the compressor is failing or “hard starting,” it cannot move enough heat to keep the room cool.
- How to solve it: A technician will need to run a diagnostic. If the compressor is dead and your unit is over ten years old, it is usually a good idea to invest in a new system.
9. Clogged Condensate Drain Line
An AC pulls a lot of water out of the air. If the drain pipe gets backed up with algae or slime, a safety float switch will shut down the cooling side of the system to prevent a flood in your home.
- How to solve it: Use a wet-dry vacuum to suck out the clog from the outdoor end of the white PVC pipe. Pouring a little vinegar down the drain line every few months can prevent future clogs.
10. Bad Blower Motor
The blower motor is the fan that pushes air through the vents. If this motor is burning out or moving too slowly, you will notice very weak airflow.
- How to solve it: Listen for squealing or grinding noises from your indoor unit. A technician can lubricate the motor or replace it if the bearings have failed.
11. Undersized AC Unit
If your air conditioner was not sized correctly for your home, it will run nonstop but never reach the desired temperature. This is very common in homes that have added rooms or have poor insulation.
- How to solve it: An expert can perform a “load calculation” to see if your unit is powerful enough. If it is too small, upgrading to a larger unit is the only permanent fix.
12. Aging System and Wear
In the harsh South Florida environment, an AC unit usually lasts about 10 to 12 years. Over time, parts become less efficient, and the metal corrodes from the salt air. Eventually, the system just cannot keep up with ninety-degree days anymore.
- How to solve it: Compare the cost of frequent repairs against the savings of a new system. A modern unit can cut your cooling costs by 30% or more.
Why Your AC Stays Stuck Above 75 Degrees
It is helpful to remember that an air conditioner is designed to lower the temperature by roughly 20 degrees compared to the air outside. On a scorching 98-degree day, your system is working perfectly if it keeps your living room at 78 degrees.
Humidity also plays a massive role in how “cool” the air feels. Your AC has to remove gallons of water from the air before it can effectively drop the temperature. If your home feels “muggy” even at 75 degrees, you might need to look into a whole-home dehumidifier or check for air leaks around your windows and doors.
FAQs
You should definitely turn it off. If the system is running but the air is not cold, the compressor is likely working overtime and could burn out. Turning it off at the thermostat prevents further damage while you wait for a technician to arrive.
You can reset most systems by turning the thermostat to “OFF” and then flipping the breaker in your electrical panel for about one minute. Turn the breaker back on and then set the thermostat to “COOL.” This often clears small electronic errors.
The three-minute rule is a safety feature that keeps the compressor from turning on too quickly after it just shut off. It protects the motor from high-pressure starts. If you just adjusted your thermostat, you might need to wait a few minutes before the cooling kicks in.
This usually happens because the outdoor heat is too intense for the system to overcome. It can also be a sign of a system that is too small for the space or one that has dirty coils and low airflow. If it happens even on cooler days, you likely need a professional tune-up.
Conclusion
Based on everything we have discussed, most cooling failures stem from simple airflow blockages or more complex mechanical issues like failing capacitors and refrigerant leaks. We recommend always starting with the basics, such as changing your filter and cleaning the outdoor unit.
However, if those simple steps do not bring back the cold air, you should not wait to call a professional. Delaying a repair in the South Florida heat usually leads to higher energy bills and more damage to the heart of your machine.
At Golden Air & Plumbing, we have spent over 10 years helping South Florida families with AC solutions. Our licensed technicians are available 24 hours a day to figure out exactly why your AC system is struggling and get it fixed fast.
Contact Us today at Golden Air & Plumbing for a same-day diagnostic!
