DIY Troubleshooting: AC Not Cooling Guide

If your AC isn’t cooling, you’re not alone. Every summer, countless households face the swelter of a malfunctioning air conditioner. Our guide is packed with practical DIY fixes to swiftly get your chilling companion back in action.

Read on and beat the heat!

Understanding How an Air Conditioner Works

Air conditioners keep your home cool by removing heat from the inside and releasing it outdoors. The heart of the system, the compressor, pumps a special substance called refrigerant through coils within the unit.

This refrigerant absorbs heat as it transforms from a low-pressure gas to a high-pressure liquid. After collecting indoor warmth, the now-heated refrigerant moves to the condenser coil, releasing its captured heat into the outside air.

The cycle is continuous: chilled refrigerant comes back inside and passes through the evaporator coil, which acts like a sponge to pull more warmth from your home’s air. As warm air blows across this cold coil via the air handler unit, it loses its heat, and moisture in that air also condenses on this coil—helping lower humidity levels.

Meanwhile, fans help circulate cooled-down and drier indoor air throughout your house through ductwork or over an open space if you have a split-system or mini-split conditioner.

This process is key for maintaining comfort during hot days while enhancing energy efficiency in your cooling efforts.

Common Causes of an Air Conditioner Not Cooling

Discover the usual suspects behind your air conditioner’s lacklustre performance. From a rebellious thermostat to a struggling compressor, several key culprits could be hindering the chill factor in your home.

Faulty Thermostat

A common culprit behind an air conditioning system not cooling is a faulty thermostat. This device acts as the command centre for your HVAC system, setting the temperature and regulating when the cool air should circulate.

Problems can arise if it’s incorrectly calibrated or simply breaks down due to wiring issues or battery failure. Homeowners may overlook this small gadget, but its proper function is crucial for indoor comfort.

To tackle thermostat troubles, first ensure it is set to “cool” rather than “heat” or “off.” Check that its programmed temperatures are correct for your desired cooling levels. It might need new batteries, an easy fix anyone can manage without special tools.

If you suspect a more complex electrical issue or incorrect calibration, consider using a thermometer to verify the accuracy of the thermostat readings before reaching out to an HVAC professional for a precise diagnosis and repair.

Blocked Airflow

Ensuring your air conditioning unit has unobstructed airflow is crucial for its cooling efficiency. Clogged or dirty filters are often the culprits behind blocked airflow, as they can obstruct the passage of cool air and strain your system.

Replacing a filthy filter with a clean one can dramatically improve your AC’s performance.

Blocked vents or ductwork in your home can also impede airflow from your central air conditioner. This affects individual rooms and may lead to increased energy bills as the system works harder to circulate air.

Regular checks of vents, combined with cleaning or vacuuming, help maintain consistent and effective airflow throughout the house.

Dirty Filter

A dirty filter is a common culprit when your air conditioning system struggles to circulate cool air. Over time, dust and debris collect on the air filter, choking off the airflow your HVAC desperately needs to function effectively.

Without adequate air passing through, cooling efficiency plummets, and parts of the unit can overheat. Replacing a clogged air filter might appear simple, but it profoundly affects the optimal performance of your central air conditioning.

Neglecting this straightforward routine maintenance puts unnecessary strain on the entire system. As dirt accumulates, cold air gets trapped inside and lowers the internal temperature of components meant to disperse heat.

This phenomenon significantly hampers an AC’s ability to keep indoor spaces comfortable during hot weather. Swiftly swapping out a soiled filter for a clean one could save you from dealing with bigger issues down the line, such as decreased performance or even overheating—a quick fix ensuring relentless summer heat stays outside where it belongs.

Malfunctioning Compressor

The heart of your air conditioning system is the compressor, and it’s crucial for pumping refrigerant through the unit. A malfunctioning compressor might be to blame if your AC isn’t cooling.

Various issues can lead to its failure; these include overheating, electrical faults or mechanical damage within the component. Recognising that a faulty compressor impacts the entire system helps you understand why prompt attention is necessary.

Regular maintenance checks can prevent common problems with compressors from getting worse. Look out for signs like strange noises from the condenser unit or an AC that cycles on and off more frequently than usual.

Checking whether circuit breakers have tripped could also reveal underlying electrical issues contributing to compressor malfunction. Taking swift action at the first sign of trouble ensures the efficient functioning of your HVAC systems and prolongs their lifespan.

Incorrectly Charged Refrigerant

If running with the wrong amount of refrigerant, your AC might struggle to cool your home. This chemical, essential for heat transfer, needs precise charging during installation or maintenance.

If it is too little, your air conditioner can’t absorb enough heat; too much may not release heat effectively. Either way, you’re left with a system that works overtime but doesn’t chill as needed.

Detecting a refrigerant issue takes skill since symptoms can resemble other problems. If you suspect an improper charge is to blame for poor performance, check for signs like ice on evaporator coils or hissing sounds indicating leaks.

Handling refrigerants requires special care due to their hazardous nature, so consider getting professional help from HVAC technicians trained in safely resolving these issues without risking health or further damage to your system.

DIY Troubleshooting Guide for an AC Not Cooling

Embark on a self-help expedition to reclaim the comfort of your cooled spaces with our DIY Air Conditioner Troubleshooting Guide. Uncover simple yet effective techniques to diagnose and fix common cooling issues, ensuring your unit regains its chill without needing immediate professional intervention.

Checking and Resetting the Thermostat

Make sure your thermostat is in the right setting to cool your home. It may seem simple, but sometimes the solution is just a switch away. Check that it’s set lower than your home’s current temperature and switched to ‘cool’.

This step can often kick-start a non-cooling air conditioner into action.

If adjusting the settings doesn’t work, try resetting the thermostat. First, turn it off or remove its batteries briefly before putting them back in place. Another option involves going to your breaker box and flipping the corresponding switch off and then on again.

A reset helps clear any glitches within your system, potentially getting things back up and running smoothly.

Replacing the Dirty Filter

Check your air conditioner’s filter if you notice a drop in cooling performance. A dirty filter can significantly restrict air flow, making it harder for your AC to circulate cooled air throughout your home.

Grab a new filter and swap out the old one—it’s usually a simple task that involves sliding the old filter out of its slot and pushing the new one into place. This quick change can enhance your system’s efficiency by up to 15%.

Cleaner filters support optimal airflow and keep energy costs down.

Regularly inspecting your filters is key to maintaining good indoor air quality and ensuring your HVAC unit runs smoothly. Experts suggest checking them monthly, especially during high-use seasons or if you have pets that shed fur and dander at home.

Keep replacements on hand so you can switch them out immediately when they get clogged with dust and dirt. A clean filter not only boosts cooling power but also extends the lifespan of an air conditioning system by preventing unnecessary strain on its components.

Clearing the Condensation Drain

Clogged condensation drains can impede your air conditioning system’s performance, leading to poor cooling. To tackle this, first, turn off your AC unit for safety. Locate your drain line—usually found near the indoor cooling coil mounted above the furnace in the basement or a utility closet.

Using a wet/dry vacuum cleaner, suction out any blockages from the drain end outside your home. To maximise suction, ensure you seal the connection between the vacuum hose and the drain line tightly with duct tape or cloth.

Check for a PVC pipe with a cap near the furnace—this is likely to be an access point to flush out debris from the inside. Open it up and pour in water and bleach to clear out algae and mildew that may have formed within.

After cleaning, ensure all caps are securely replaced on pipes and joints checked for leaks, which could affect air vents’ efficiency. Maintaining these lines prevents potential water damage and keeps cool air flowing through your heat pump effectively.

Diagnosing Duct Malfunctions

Inspect your air ducts carefully to ensure they are free from blockages or damage that could restrict cool air flow through your home. Look for any disconnected sections, tears in the flexible tubing, or crushed parts that might indicate a problem.

Debris, such as dirt and dust, can accumulate over time, reducing efficiency and leading to malfunctions in the system.

Perform regular checks for signs of wear and tear on your HVAC ducts, especially if you notice uneven cooling or strange noises when the AC is running. Remove any visible obstructions gently to improve airflow and prevent potential short-cycling of the unit, which happens when disrupted air causes frequent on-and-off cycling.

Regular maintenance like this can help diagnose issues early and extend the life of your heating and cooling system.

Cleaning the Area Around the Compressor

Ensure that your air conditioning unit’s compressor has enough room to breathe. Over time, leaves, dirt, and debris can accumulate around it, obstructing airflow and reducing efficiency.

Start by removing any visible waste with gloves and a rubbish bag. Trim back bushes or plants that might crowd the compressor to allow at least 60 cm of clear space on all sides.

Next, gently brush off any loose dirt from the exterior of the compressor using a soft-bristled brush. Be cautious not to bend or damage the delicate fins on the condenser coils. If you find stubborn grime, mix some mild detergent with water and carefully wipe the surfaces without saturating any electrical components.

Once you’ve removed debris and cleaned surfaces, your air conditioner’s compressor will have improved odds of running smoothly and keeping your home cool.

Cleaning Dirty Coils

Dirty coils in your air conditioner can cause the system to struggle and use more energy, leading to inefficiency. When these coils are clogged with dust and debris, they can’t transfer heat effectively, so your AC must work overtime.

To clean them, switch off the power to avoid any electrical hazards. Gently vacuum away loose dirt from the coils. For a deeper clean, apply a mild detergent mixed with water or use a commercial coil cleaner following the instructions on the label.

After scrubbing the coils with a soft brush to remove stubborn grime, rinse them carefully with low-pressure hose water if they’re outdoor condenser coils. Indoor evaporator coils may need just wiping down as too much water could damage components inside your home.

Regularly cleaning these parts is crucial for preventing refrigerant leaks and ensuring that fresh, cool air circulates throughout your space efficiently without circulating pollutants or allergens that could harm your health.

Decoding Common Air Conditioner Noises During Troubleshooting

A hissing sound from your air conditioning system often signals a refrigerant leak. This can affect cooling efficiency and requires immediate attention to prevent damage to the environment and your wallet.

Refrigerant leaks may harm performance and pose health risks, making it crucial to address them promptly.

Screeching noises signal problems with the fan motor or compressor in many cases. These are critical components of your unit’s ability to cool your home, indicating that parts might be broken or worn out.

Meanwhile, gurgling sounds suggest issues within the refrigerant lines, possibly due to improper phase conversion from liquid to gas during operation. Listen for harsh humming, which may mean that fan blades or coil fins have come loose or become dirty – they need cleaning or potential replacement if bent significantly.

When to Call an HVAC Professional

Sometimes, your air conditioner issues are beyond a simple fix. If you’ve attempted basic troubleshooting and the unit still isn’t cooling, it’s time to contact an HVAC professional.

They have the skills to safely handle refrigerant leaks, which can be dangerous if not addressed properly. These specialists come equipped with the specific tools and expertise necessary to locate and repair any leaks.

Electrical problems within your system also warrant a call to an expert. Attempting repairs on high-voltage components without proper training can injure or damage your system.

Professionals will ensure your air conditioning systems function optimally while adhering to safety standards. If you notice persistent problems despite changing filters and cleaning coils, this could indicate deeper issues like a faulty compressor – another scenario where calling an HVAC specialist is crucial for efficiency and safety.


In conclusion, this guide equips you with the know-how to tackle a non-cooling AC unit head-on. Break down each issue methodically and apply these hands-on solutions before summer heat overwhelms your space.

Should complexities arise, don’t hesitate to seek professional help. Remember, comfort in your home is paramount; keep it breezy by maintaining a well-functioning air conditioner.

Stay cool and confident as you DIY your way to optimal indoor temperatures.

If your air conditioner is making strange noises, please refer to our detailed guide on understanding and resolving common air conditioner noises for further assistance.


1. What should I check first if my AC is not cooling?

Start by checking your smart thermostat settings and inspecting the fuse connected to your split system air conditioner to ensure they are functioning correctly.

2. Can low refrigerant gas be the reason for my AC’s poor performance?

A common issue with AC units is low refrigerant gas levels, which can cause your system to stop cooling effectively.

3. Are there any alternatives to using my air conditioning that are more energy-efficient?

Indeed, you could opt for ceiling fans or heat pumps as energy-efficient HVAC alternatives that can keep you cool without heavily relying on traditional refrigeration methods.

4. What part does an HVAC heater play when my split system air conditioner isn’t cooling?

Your heater should normally not affect the cooling process; however, ensure it’s turned off because running both simultaneously may impact temperature control.

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