Heat Pumps
Why Your AC Unit Takes a Long Time to Cool (And How to Fix It)
By HVAC.com•March 3, 2025
If you’ve noticed that your air conditioning unit takes a long time to cool your home, you’re not alone. Many homeowners experience this frustrating problem, especially during the peak of summer when you need cool air the most.
A slow-to-cool AC can lead to discomfort and higher energy bills, so it’s important to identify the cause and address it promptly to restore comfort. Keep reading as HVAC.com explores why your AC unit might be taking longer than expected to cool your space and what you can do to solve the issue.
The 9 Most Common Reasons Your AC Is Slow to Cool
1. Dirty Air Filter
Many air conditioner problems – including an AC that takes a long time to cool your home – can be traced to a clogged or dirty air filter. Air filters trap dust, dirt, and debris, but over time they can become clogged, restricting airflow and making it harder for the system to cool the air efficiently. This reduces the overall performance of your AC and makes it work harder to achieve the desired temperature.
How to fix it: Check the air filter monthly and replace it if it looks clogged and dirty. Most filters need to be changed every 1-3 months, depending on the type and usage. Regularly replacing your air filter ensures optimal airflow and efficiency.
2. Low Refrigerant Levels
Your AC uses refrigerant to cool the air in your home by absorbing heat and transferring it outside. If the refrigerant levels are low due to a leak in the system, the unit may struggle to cool effectively, causing delays in reaching your desired temperature.
How to fix it: If you suspect that your AC’s refrigerant levels are low, contact an HVAC technician. They will be able to check for leaks, recharge the refrigerant, and ensure that the system is functioning properly. Never attempt to handle refrigerant on your own, as it can be hazardous.
3. Faulty Thermostat
Another common culprit behind an AC that takes too long to cool is a malfunctioning thermostat. If the thermostat is not accurately reading the temperature or if it’s placed in an area with poor airflow (like near a heat source), it can send incorrect signals to the unit, causing it to work inefficiently.
How to fix it: Try recalibrating the thermostat, or check for issues like dead batteries or a loose connection. If the problem persists, you may need to replace the thermostat. Upgrading to a programmable or smart thermostat can also help ensure more precise temperature control and efficient cooling.
4. Dirty Coils
The evaporator and condenser coils absorb and release heat from the air. Over time, these coils can accumulate dirt and debris, which can restrict their ability to function effectively. When the coils are dirty, your AC unit may struggle to cool the air, leading to longer cooling times.
How to fix it: Cleaning the coils is an important maintenance task. If you’re comfortable doing it yourself, you can carefully clean the coils using a soft brush or coil cleaner. Otherwise, it’s recommended to hire a professional HVAC technician who can perform a thorough cleaning to prevent further issues.
5. Poor Insulation or Air Leaks
Sometimes, the problem may not be with the AC unit itself, but with the home’s insulation. If your home is poorly insulated or has air leaks around windows and doors, the cool air from the AC can escape, leading to longer cooling cycles and making it harder for the unit to maintain the desired temperature.
How to fix it: Check for gaps or cracks around windows, doors, and ducts, and seal them to prevent cool air from escaping. Insulating your home properly can also help the AC unit cool your home more effectively, reducing the workload on the system and improving its efficiency.
6. Oversized or Undersized AC Unit
An AC unit that’s too small for your home will have trouble cooling it effectively, while a system that’s too large may turn on and off too often, causing it to waste energy. If your AC unit isn’t the right size for your home, it could be one of the reasons it’s taking longer than normal to cool.
How to fix it: If your AC unit is improperly sized, you may need to have a professional assess your cooling needs and recommend an appropriately sized system. While this can be an expensive solution, it can significantly improve your home’s comfort and energy efficiency in the long run.
7. An Old and Inefficient AC Unit
Older air conditioning units tend to become less efficient as they age. They might struggle to cool your home effectively, take longer to reach the desired temperature, and consume more energy. Additionally, older units often lack modern energy-saving technology, leading to higher electricity bills and less reliable performance.
How to fix it: If your AC unit is over 15 years old and is taking significantly longer to cool, it might be time to consider replacing it with a more energy-efficient model. Newer air conditioners use advanced technology to cool more efficiently and provide better long-term savings on energy costs.
8. Leaky Air Ducts
Air ducts are responsible for distributing cooled air throughout your home. If the ducts have leaks or cracks, cool air can escape before it reaches its intended destination. This can cause your AC unit to work harder and take longer to cool the home, as it struggles to make up for the lost air.
How to fix it: Inspect your ducts for visible leaks or cracks, and seal any gaps with mastic or aluminum foil tape. It’s often best to hire a professional to inspect and repair your ductwork thoroughly, as they can also find all of the leaks in areas that are difficult to access, ensuring maximum airflow and efficiency.
9. Blocked or Covered Air Vents
Air vents allow cooled air to flow into the rooms of your home. If your vents are blocked by furniture, rugs, or other obstacles, the airflow can be restricted, preventing your AC from cooling efficiently. In some cases, dirty or clogged vents can also contribute to reduced airflow.
How to fix it: Ensure that all air vents are unobstructed and clean. Remove any furniture or items blocking the airflow, and vacuum the vents regularly to clear out dust and debris. This simple step can help your AC unit cool your space more quickly and efficiently.
The Importance of Yearly AC Maintenance
Regular AC maintenance is key to preventing many of the issues that cause your AC unit to take a long time to cool. A professional technician can inspect your system, clean the coils, check refrigerant levels, replace the air filter, and ensure everything is running smoothly. By scheduling an annual tune-up, you can catch potential problems early, avoid costly repairs, and extend the life of your air conditioning unit.