Why Is My AC Not Cooling? 10 DIY Fixes Before Calling a Technician
It is frustrating when your AC is running but not cooling — especially during Trivandrum's sweltering summer months. Before you call a technician and spend money on repairs, there are several DIY troubleshooting steps you can try. In fact, about 60% of AC cooling issues can be resolved with simple fixes that take just minutes.
This comprehensive guide walks you through 10 common causes of AC not cooling and how to fix them yourself. We have organized them from easiest to more complex, so start with #1 and work your way down. If none of these solve your problem, then it is time to call a professional.
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Call AC Technician Now10 DIY Fixes for AC Not Cooling
Check and Clean Air Filters
Dirty filters are the #1 cause of AC cooling problems. When filters get clogged with dust, airflow is restricted, reducing cooling efficiency by up to 30%.
How to Fix:
- Turn off the AC and unplug it
- Locate the air filter (usually behind the front panel)
- Remove the filter carefully
- If reusable: Wash with mild soap and water, let dry completely
- If disposable: Replace with a new filter of the same size
- Reinstall the clean/dry filter
- Turn AC back on and check cooling after 30 minutes
Call a professional if: If cleaning filters does not improve cooling after 1 hour of operation.
Check Thermostat Settings
Sometimes the issue is simply incorrect thermostat settings. This is more common than you think!
How to Fix:
- Ensure thermostat is set to COOL mode (not HEAT or FAN)
- Set temperature at least 3-5°C below room temperature
- Check if thermostat batteries need replacement (for wireless remotes)
- Ensure the thermostat sensor is not blocked by curtains or furniture
- Wait 10-15 minutes for the AC to start cooling after adjusting settings
Call a professional if: If thermostat display is blank or unresponsive (may need replacement).
Inspect the Outdoor Unit
The outdoor condenser unit needs proper airflow to release heat. Blockages can severely impact cooling.
How to Fix:
- Go outside and locate the outdoor unit
- Check for debris: leaves, grass, dirt, or objects blocking the unit
- Ensure there is at least 2 feet clearance around all sides
- Clean the condenser fins gently with a soft brush or cloth
- Remove any plants or bushes growing too close to the unit
- Check that the outdoor fan is spinning when AC is running
Call a professional if: If the outdoor fan is not spinning or makes unusual noises.
Check for Ice on Evaporator Coils
Ice formation on indoor coils blocks airflow and stops cooling. This usually happens due to low airflow or low refrigerant.
How to Fix:
- Open the front panel of the indoor unit
- Look for visible ice or frost on the copper coils behind the filter
- If ice is present: Turn off AC completely and switch to FAN mode only
- Let the ice melt naturally (2-4 hours) — do not scrape or force it
- Place towels below the unit to catch dripping water
- Once thawed, turn AC back on and check if cooling resumes
Call a professional if: If ice forms again within 24 hours (indicates low gas or other issues).
Clean the Condensate Drain Line
A clogged drain line can cause water backup and trigger safety switches that shut down the AC.
How to Fix:
- Locate the drain pipe (usually a PVC pipe near the outdoor unit)
- Check if water is draining properly when AC runs
- Use a wet/dry vacuum to suck out clogs from the drain line end
- Alternatively, pour a mixture of warm water and mild bleach down the drain
- Check that water flows freely through the pipe
Call a professional if: If the drain line is damaged or clogs persist after cleaning.
Check Circuit Breakers and Power Supply
Electrical issues can cause the AC to run but not cool properly, or trip intermittently.
How to Fix:
- Check your home's electrical panel for tripped breakers
- Reset any tripped breakers by switching off and then on
- Ensure the AC is plugged in properly (for portable units)
- Check if the outdoor unit has power (listen for fan/compressor noise)
- If breaker trips repeatedly, do not reset again — call a professional
Call a professional if: If breakers trip repeatedly or outdoor unit has no power.
Inspect Air Vents and Ducts
Blocked or closed vents restrict airflow and reduce cooling efficiency throughout your home.
How to Fix:
- Walk through your home and check all air vents
- Ensure all vents are fully open (not closed or partially blocked)
- Move furniture, curtains, or objects blocking vents
- Check for dust buildup on vent covers and clean if needed
- Ensure doors to rooms you want cooled are open for airflow
Call a professional if: If some rooms never cool despite open vents (possible duct issues).
Check Refrigerant Lines for Leaks
Low refrigerant (gas) is a common cause of poor cooling. Visual inspection can reveal obvious leaks.
How to Fix:
- Inspect the copper refrigerant lines connecting indoor and outdoor units
- Look for oil stains or wet spots on the lines (indicates leaks)
- Listen for hissing sounds near the indoor or outdoor unit
- Check for ice formation on the larger copper line (low gas sign)
- Note: Only a professional can properly check and refill refrigerant
Call a professional if: If you suspect low refrigerant — this requires professional equipment to fix.
Reset the AC Unit
Sometimes a simple reset can resolve electronic glitches affecting cooling performance.
How to Fix:
- Turn off the AC using the remote control
- Unplug the AC from the power outlet (or turn off breaker)
- Wait for 5 minutes (this allows capacitors to discharge)
- Plug the AC back in (or turn breaker on)
- Turn on the AC and set to COOL mode
- Wait 15-20 minutes to see if cooling improves
Call a professional if: If AC still does not cool after reset and other checks.
Check for Compressor Issues
The compressor is the heart of your AC. If it is not working, the AC will not cool.
How to Fix:
- Go to the outdoor unit while AC is running
- Listen for the compressor humming or vibrating
- Feel the larger copper line — it should be cold (not warm)
- Check if the outdoor fan is spinning properly
- If compressor is silent and line is not cold, there may be a compressor issue
Call a professional if: Immediately — compressor issues require professional diagnosis and repair.
When to Call a Professional AC Technician
While DIY fixes can solve many AC cooling issues, some problems require professional expertise and equipment. Call a technician if:
- You have tried all 10 steps above and AC still does not cool
- You suspect low refrigerant (gas) levels
- The compressor is not running or makes unusual noises
- Ice forms repeatedly on coils even after thawing
- There are electrical issues like repeated breaker trips
- You see refrigerant leaks (oil stains on lines)
- The AC is over 10 years old and cooling poorly
Professional AC Service in Trivandrum
Certified technicians, same-day service, transparent pricing. We diagnose and fix all AC cooling issues.
Book AC Repair NowPreventive Maintenance Tips to Avoid AC Cooling Issues
Clean Filters Monthly
Check and clean AC filters every 2-4 weeks during heavy use
Annual Deep Service
Get professional AC service at least once a year before summer
Keep Outdoor Unit Clear
Maintain 2 feet clearance around the outdoor condenser unit
Check Thermostat Settings
Set temperature 24-26°C for optimal efficiency and comfort
Use Fan Mode
Switch to FAN mode for 30 minutes daily to reduce moisture
Schedule Pre-Season Check
Get AC checked before summer to avoid peak-season breakdowns
Frequently Asked Questions
Why is my AC running but not cooling?
The most common reasons your AC runs but does not cool are: dirty air filters blocking airflow, low refrigerant gas levels, thermostat set incorrectly, blocked outdoor unit, frozen evaporator coils, or compressor issues. Try cleaning filters and checking thermostat settings first before calling a technician.
How do I fix my AC not cooling?
To fix an AC that is not cooling: 1) Clean or replace dirty air filters, 2) Check thermostat is set to COOL mode, 3) Ensure outdoor unit is not blocked, 4) Clean the outdoor condenser coils, 5) Check for ice on coils and turn off AC to thaw, 6) Ensure all vents are open. If these do not work, call a professional for gas refilling or compressor check.
Should I turn off AC if it is not cooling?
Yes, turn off your AC if it is not cooling properly. Running a malfunctioning AC can cause further damage to the compressor and other components. Turn it off, check for obvious issues like dirty filters or blocked vents, and call a technician if basic troubleshooting does not resolve the problem.
How long should I wait after cleaning filters?
After cleaning or replacing AC filters, wait about 30 minutes to 1 hour for the system to stabilize and show improved cooling. If you do not notice improvement after 1 hour of operation, there may be other issues requiring professional attention.
Can low gas cause AC to not cool?
Yes, low refrigerant (gas) is one of the most common causes of AC not cooling properly. Signs of low gas include: ice formation on the larger copper line, hissing sounds from the unit, AC running continuously without reaching set temperature, and warm air from vents. Only a professional technician can properly check and refill refrigerant.
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