How to fix a central AC with inconsistent cooling throughout the day

Diagnosing and repairing an AC system with inconsistent cooling doesn’t have to be intimidating. By following these DIY steps, you can address many common issues, from clogged air filters to electrical problems, and get your system back to staying cool and keeping your system in top shape!

The troubleshooting information in this article is based on general service manuals and may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model or contact us for more help.

Understand the problem

Before you get started, it’s important to understand what might be causing your AC to act up. Inconsistent cooling is usually a result of one of these issues:

• Dirty or clogged air filters
• Low refrigerant levels
• Malfunctioning thermostat
• Airflow problems (blocked ducts, dirty coils, etc.)

When the air conditioner isn’t cooling evenly or fluctuating in temperature throughout the day, it’s often a sign that one of these parts is to blame. In the following sections, we’ll walk through how to troubleshoot these issues yourself, so let’s get started. 

Safety first

Before you dive into any repairs, it’s always a good idea to make sure you’re staying safe. Working on your AC can be a bit tricky, but if you follow these simple safety tips, you’ll be good to go:

• Turn off the power: This is the most important step! Make sure you shut off the power to your AC unit at the thermostat and at the main breaker. You don’t want to risk any electrical accidents while working on your system.
• Have the right tools: Grab a few basic tools, like a screwdriver, a multimeter (for testing electrical components), and gloves. Having the right tools makes everything easier and safer.
• Protect yourself: Wear gloves and safety glasses, especially if you’re cleaning parts, dealing with refrigerant, or handling any electrical components. It’s just a good idea to keep yourself safe.

Start with the basics – check the thermostat

If your thermostat is malfunctioning, it can cause your AC to cool inconsistently. Here’s how to check if the thermostat is the culprit:

1. Check the settings: Make sure the thermostat is set to “cool” mode and the temperature is set to a lower value than the current room temperature.
2. Recalibrate: If the thermostat seems unresponsive or is showing incorrect temperatures, it may need recalibration. Some models have a small reset button you can press, while others may require you to adjust the internal settings. Check your manual for specific instructions.
3. Replace the batteries: If your thermostat runs on batteries, replace them to rule out the possibility of dead batteries affecting performance.
4. Test with a multimeter: If you suspect the thermostat is faulty and you’re comfortable testing electrical components, use a multimeter to check the connections. Set the multimeter to the appropriate voltage setting and test the thermostat terminals to ensure they’re receiving power.

Inspect the air filter

A dirty or clogged air filter is one of the most common reasons your AC might be cooling inconsistently. When the filter is full of dust and dirt, it blocks airflow, making it harder for your system to cool the air properly. Here’s how to check and clean it:

1. Locate the filter: Your AC’s air filter is usually located near the return air duct or inside the blower compartment.
2. Remove the filter: Gently pull the filter out of its slot. If it’s clogged with dust, dirt, and debris, it’s time to clean or replace it.
3. Clean or replace: If the filter is washable, rinse it under water, let it dry completely, and place it back in. If it’s disposable, replace it with a new one of the same size and type.
4. Check airflow: Once the filter is clean or replaced, turn the AC back on and check the airflow. It should feel stronger and more consistent.

Check the air vents and ductwork

If your air filter is good, but you’re still experiencing uneven cooling, it might be a problem with the airflow in your home. Here’s how to check your air vents and ductwork:

1. Inspect air vents: Go around the house and make sure all the vents are open and unobstructed. Sometimes furniture or rugs can block vents, reducing airflow.
2. Check for leaks: Inspect your ductwork for any visible cracks, holes, or disconnected sections. Leaks in your ducts can result in the cool air escaping before it reaches the rooms.
3. Seal leaks: If you find any leaks, seal them with duct tape or use a specialized duct sealant. Make sure to cover both the holes and the seams to restore optimal airflow.
4. Test the airflow: After sealing any leaks, test the airflow by turning on your AC and feeling the air coming out of the vents. It should be consistent and strong.

Investigate the evaporator and condenser coils

The evaporator and condenser coils are key components in your AC’s cooling process. If they’re dirty or iced over, they can seriously impact your AC’s performance. Here’s how to check and clean them:

1. Turn off the power to your unit before cleaning any coils.
2. Inspect the evaporator coils: These coils are usually located inside the air handler, where the air is cooled. Look for signs of dirt buildup or ice formation. If you see ice, it could indicate a refrigerant issue or airflow problem.
3. Inspect the condenser coils: These are located in the outdoor unit. If they’re dirty, you might notice reduced cooling performance. Dust and debris can accumulate on the coils, blocking airflow.
4. Evaporator coils: Use a soft brush to gently remove dust, or use a coil cleaner available at most hardware stores.
5. Condenser coils: Use a fin comb or coil brush to remove debris, and hose the coils down with water (just make sure not to damage the components).
6. Check for ice buildup: If the evaporator coils are iced over, it may indicate a refrigerant problem or poor airflow. Let the ice melt, but keep an eye on the system to see if the issue persists.

Refrigerant levels – low refrigerant can be the culprit

Low refrigerant levels can cause inconsistent cooling because the AC unit can’t absorb enough heat from the air. Unfortunately, if refrigerant levels are low, there’s likely a leak somewhere in the system. Here’s what you can do:

1. Check for signs of low refrigerant: The most common sign of low refrigerant is that the AC blows warm air or doesn’t cool evenly. You may also see ice buildup on the coils.
2. Test refrigerant pressure: You can check refrigerant levels using a set of manifold gauges, but this can be tricky without experience. If the pressure readings are low, you may need to recharge the refrigerant.
3. Find a leak: If you’re comfortable using a multimeter, you can check for electrical shorts in the system that could be affecting the refrigerant pressure, but leaks are usually best handled by a pro. If you suspect a leak, you can purchase a leak detection kit or check for oily spots around the refrigerant lines. If you find a leak, the refrigerant needs to be recharged, which should be done with caution.

Inspect the compressor and fan

The compressor and fan play vital roles in keeping the AC system running efficiently. If either one isn’t working properly, you’ll likely experience inconsistent cooling. Here’s how to inspect both parts:

1. If you hear strange noises like grinding, buzzing, or clicking from the compressor (the unit outside), it might be a sign of an internal issue or a failing motor.
2. Check the fan inside the compressor unit for smooth operation. If it’s not turning or making unusual sounds, the fan motor could be failing.
3. Turn off the power to the unit before inspecting the fan blades. Look for any dirt buildup or debris that could be obstructing the blades. Clean them gently using a brush or cloth.
4. If the fan blades are fine, but the fan motor is struggling, you can apply some light oil to the motor bearings. Be sure to check the manufacturer’s instructions for the type of lubricant to use.

Additional information

Thanks for reading! We hope this guide helped you fix your central AC. If you still need some replacement parts, grab your model number and head over to AppliancePartsPros.com. We offer over two million parts and most orders arrive in two business days. If you need some help with finding the right part or placing an order, you can contact our team at 1 (877) 477-7278.

While you’re waiting for your new part to arrive, you can explore our DIY blog and watch thousands of video tutorials on our YouTube channel.

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