Aircon Not Cooling? 9 Causes & Fixes (DIY Guide Before You Call a Technician)

❄️🔧 From dirty filters to low refrigerant—diagnose and fix your air conditioner’s cooling problems yourself

It’s a sweltering December afternoon in Johannesburg. The temperature outside is 34°C. You’ve just come home from work, sweating through your shirt. You grab the remote, point it at your aircon, and press the power button. The unit hums to life. The fan spins. But the air coming out… is warm. Not cool. Definitely not cold.

Your heart sinks. “Not now,” you think. “Not during a heatwave.”

I’ve been there. And here’s what I’ve learned after helping hundreds of homeowners troubleshoot their aircons: most cooling problems have simple fixes. Dirty filters. Incorrect settings. A tripped breaker. These are things you can fix yourself in minutes—without paying a R600-R1,000 call-out fee.

In this guide, I’ll walk you through 9 common reasons why your aircon is not cooling. For each cause, I’ll explain how to diagnose it and how to fix it—step by step. And when you’ve tried everything and still have aircon blowing warm air, I’ll tell you exactly when to call a professional.

For more troubleshooting help, check same-day aircon repair services and our maintenance checklist. Ready to diagnose your aircon? Let’s go.

🔍 Quick Diagnostic: Is This a DIY Fix or Professional Job?

Before diving into each cause, use this quick flowchart to decide if you should keep reading (DIY) or call a technician immediately.

🧹 Cause #1: Dirty or Blocked Air Filter (Most Common!)

This is the #1 reason why aircon is not cooling properly. And it’s the easiest fix.

How to diagnose: Remove the air filter (usually behind the front panel of the indoor unit). Hold it up to light. Can you see through it? If not, it’s clogged with dust, pet hair, and debris.

Why this causes poor cooling: A blocked air filter restricts airflow across the evaporator coils. Without adequate airflow, the coils get too cold, ice up, and the unit can’t absorb heat from your room. The air coming out feels weak and barely cool.

DIY fix (5 minutes):

1. Turn off the aircon and unplug it (or turn off the isolator switch)
2. Open the front panel and remove the filter(s)
3. Vacuum the filter with a brush attachment
4. Wash with warm soapy water (not hot—can warp plastic)
5. Rinse thoroughly and let dry completely (don’t install wet)
6. Reinstall filter and close panel
7. Restart aircon—cooling should improve within 10-15 minutes

Prevention: Set a monthly reminder on your phone. Filter cleaning takes 5 minutes and saves you hundreds in electricity and repairs.

🎮 Cause #2: Wrong Remote Settings (Embarrassingly Common!)

I can’t tell you how many service calls I’ve seen where the “broken” aircon was just on the wrong setting. Don’t be embarrassed—it happens to everyone.

How to diagnose: Check your remote control display. Look for these mode indicators:

• ❄️ Cool mode (snowflake icon): This is what you want for cooling
• 💨 Fan mode (fan icon): Only runs the fan—no cooling at all
• 💧 Dry mode (water droplet icon): Dehumidifies but cools very little
• ☀️ Heat mode (sun icon): Blows hot air (winter mode)
• 🔄 Auto mode: May switch between modes unpredictably

Why this causes “aircon blowing warm air”: If your unit is in Fan mode, it’s just circulating room air—no cooling. If it’s in Heat mode, it’s actively warming your room. If it’s in Dry mode, cooling is minimal.

DIY fix (10 seconds): Press the “Mode” button on your remote until the ❄️ snowflake icon appears. Set temperature to 22-24°C (not 16°C—that won’t cool faster, it’ll just make the unit run longer). Wait 5-10 minutes. Your ac not cooling properly problem just disappeared.

⚡ Cause #3: Tripped Circuit Breaker or Blown Fuse

Sometimes the outdoor unit (compressor) loses power while the indoor fan still runs. This results in room-temperature air blowing from your vents.

How to diagnose: Go to your electrical distribution board (fuse box). Look for a breaker labeled “Aircon,” “HVAC,” or “Outdoor Unit.” Is it in the “off” position or halfway between on and off? If yes, it’s tripped. Also check if the outdoor unit’s isolator switch (near the unit) is turned on.

Why this causes poor cooling: The indoor fan runs, making you think the aircon is working. But the outdoor compressor (which does the actual cooling) has no power. So you get fan-only air—warm and useless for cooling.

DIY fix (1 minute):

1. Turn the breaker fully to “off” position
2. Wait 10 seconds
3. Flip it back to “on” position
4. Check if the outdoor unit’s fan starts spinning
5. If it trips again immediately, call a professional (there’s an electrical fault)

When to call a pro: If the breaker trips repeatedly, don’t keep resetting it. This indicates a serious electrical problem—short circuit, faulty compressor, or overloaded circuit. Call a licensed electrician or aircon technician.

Read our electrical safety tips for homeowners for more guidance.

🧊 Cause #4: Frozen Coils (Ice Build-Up)

If you see ice forming on the indoor unit’s coils or refrigerant pipes, your aircon is not cooling because the coils are frozen solid.

How to diagnose: Turn off the aircon and open the front panel. Look at the metal fins (evaporator coils). Do you see ice or frost? Also check the thick refrigerant pipe (the one with insulation)—if it’s frozen or sweating excessively, you have a problem.

Why this happens: Ice build-up is usually caused by:

• Dirty air filter (restricted airflow)
• Low refrigerant (gas leak)
• Dirty evaporator coils
• Fan motor not running properly

DIY fix (2-4 hours, mostly waiting):

1. Turn off the aircon completely (remote and isolator switch)
2. Turn on the fan mode only (no cooling)—this helps melt ice faster
3. Wait 2-4 hours for all ice to melt completely
4. Clean or replace the air filter
5. Restart in cool mode
6. If ice returns within an hour, call a professional (likely low refrigerant)

Related reading: Aircon refrigerant leak signs and maintenance checklist.

💨 Cause #5: Low Refrigerant (Gas Leak)

If your aircon is low on refrigerant (gas), it can’t absorb enough heat from your room. This is a common cause of aircon blowing warm air—and it requires professional repair.

How to diagnose (professional tools needed):

• The aircon runs but cooling is very poor or non-existent
• The suction pipe (thick insulated pipe) is not cold to the touch
• Ice forms on the indoor unit or outdoor unit connections
• You hear a hissing sound (refrigerant leak)
• Your electricity bill has increased significantly (compressor running longer)

Why this happens: Refrigerant doesn’t get “used up”—it circulates in a sealed system. If you’re low on gas, you have a leak. Leaks can occur at pipe connections, through pinholes in copper pipes, or from damaged valves.

Is this DIY? NO. Refrigerant handling requires SAQCA certification (legal requirement). It’s illegal to handle refrigerants without a license. Refrigerants (R32, R410A) are also environmentally harmful if released.

Professional fix: A certified technician will:

1. Locate the leak using electronic leak detector or UV dye
2. Repair the leak (braze/solder or replace damaged pipe)
3. Vacuum the system to remove moisture and air
4. Recharge with the correct amount of refrigerant
5. Test the system for proper operation

Typical cost: R800-R1,500 for leak detection + R800-R2,500 for gas refill (depending on unit size and refrigerant type). Read our complete gas refill cost guide.

Related reading: Aircon refrigerant leak signs and repair and R32 vs R410A guide.

🔧 Cause #6: Compressor Issue (The Heart of Your Aircon)

The compressor is the heart of your air conditioner. If it fails, your aircon is not cooling at all—and you’ll hear unusual sounds or nothing at all from the outdoor unit.

How to diagnose:

• Go outside to the outdoor unit while the aircon is set to Cool mode
• Is the fan on the outdoor unit spinning? (Listen for the hum)
• Is the compressor making a loud humming or buzzing sound but not starting?
• Do you hear a clicking sound every few minutes (compressor trying to start)?
• Is the outdoor unit vibrating excessively?

Common compressor issue problems:

• Failed start capacitor: The compressor tries to start but can’t (clicking sound). This is repairable.
• Burnt out compressor: The compressor is dead—needs replacement (R4,000-R8,000+ for parts).
• Compressor thermal overload: The compressor has overheated and shut down (resets after cooling, 30-60 minutes).
• Electrical fault: No power reaching the compressor (tripped breaker, faulty contactor, damaged wiring).

Is this DIY? NO. Compressor diagnosis and repair requires specialized electrical knowledge, refrigerant handling, and proper tools. Attempting DIY compressor repair is dangerous and will void warranties.

Professional fix: A technician will test the compressor windings, check the capacitor, measure voltage, and diagnose the exact failure. Compressor replacement is expensive (often R5,000-R12,000) and sometimes costs more than a new aircon for older units.

The 50% Rule: If repair costs exceed 50% of a new unit’s price, replace the aircon. Read our aircon repair vs replacement guide.

Related reading: Aircon compressor problems explained and capacitor failure symptoms.

🌿 Cause #7: Dirty Outdoor Unit Coils

The outdoor unit (condenser) needs to dump heat from your home into the outside air. If its coils are clogged with dust, leaves, or debris, it can’t release heat efficiently—and your indoor cooling suffers.

How to diagnose: Go outside to your outdoor compressor unit. Look at the metal fins on all sides. Are they covered in dust, grass clippings, leaves, or cottonwood fluff? Can you see light through them? If not, they’re clogged.

Why this causes poor cooling: The outdoor unit rejects heat from your home. Clogged coils block airflow, reducing heat rejection by 30-50%. The compressor works harder, runs longer, and cooling capacity drops.

DIY fix (15-20 minutes, with caution):

1. Turn off the aircon at the isolator switch (near outdoor unit)
2. Remove large debris (leaves, grass) by hand
3. Use a soft brush or vacuum with brush attachment to remove surface dust
4. Spray a gentle stream of water from a garden hose through the coils from inside out (don’t use pressure washer—it bends fins)
5. Let the unit dry completely (30 minutes)
6. Restart and check cooling performance

Prevention: Keep the area around your outdoor unit clear of vegetation (at least 300mm clearance on all sides). Trim bushes and trees regularly. Cover the unit during autumn if leaves are falling, but remove the cover before running.

Read our complete coil cleaning guide for detailed instructions.

🌀 Cause #8: Fan Motor Problems (Indoor or Outdoor)

If either the indoor fan or outdoor fan isn’t running properly, your ac not cooling properly problem is likely fan-related.

How to diagnose indoor fan issues:

• Turn on the aircon in Fan mode (no cooling)
• Do you feel air coming from the indoor unit vents?
• Is the airflow very weak compared to normal?
• Do you hear unusual noises (clicking, rattling, screeching) from the indoor unit?

How to diagnose outdoor fan issues:

• Go outside while the aircon is set to Cool mode
• Is the outdoor fan spinning? (Look through the grille)
• If the compressor is running but the fan isn’t, the outdoor unit will feel very hot

Why this causes poor cooling:

• Indoor fan not working: No air circulates over the cold coils. The unit gets icy cold but can’t transfer that cold to your room.
• Outdoor fan not working: The outdoor unit can’t dump heat. The compressor overheats and may shut down. Cooling capacity drops to near zero.

Is this DIY? Maybe (simple fixes only).

• DIY if: The fan is obstructed by debris, or the filter is so clogged that airflow is blocked (clean filter first).
• Call a pro if: The fan motor is making grinding/screeching noises, won’t start, or spins very slowly. This indicates a failed motor bearing, dead capacitor, or electrical fault.

Professional fix: Fan motor replacement costs R800-R2,500 for parts plus labour. Capacitor replacement costs R300-R600 plus labour.

Related reading: Aircon fan not working guide and fan motor problems explained.

📏 Cause #9: Undersized Unit for Your Room

Sometimes the aircon isn’t broken—it’s just too small for the space you’re trying to cool. This is a design/installation problem, not a repair issue.

How to diagnose:

• The aircon runs continuously (never cycles off)
• The room never reaches the set temperature on hot days
• The air coming out of the vents is cold, but the room stays warm
• You’ve added insulation, sealed windows, or closed doors—still not cooling
• Your room has large windows, high ceilings, or poor insulation

Why this happens: You need approximately 600 BTU per square meter of room space. A 9,000 BTU unit can cool about 15m². If your room is 25m² with afternoon sun, you need 15,000+ BTU. The small unit runs 24/7 but can’t overcome the heat load.

DIY fix? Not really—you need a larger unit or additional unit.

Solutions:

• Add a second unit: Install another aircon in the same space (two smaller units working together)
• Replace with larger unit: Install a properly sized aircon (R8,000-R15,000+ depending on size)
• Reduce heat load: Add ceiling insulation (R5,000-R15,000), install blinds/curtains, seal gaps around windows

Use our BTU size calculator to determine the correct size for your room. Read best aircon for small rooms or best aircon for large homes for buying guidance.

📞 When to Call a Professional (Don’t DIY These)

After trying the DIY fixes above, if your aircon is not cooling, it’s time to call a professional. Also call immediately if you experience any of these:

How to find a reliable technician: Use our installer selection guide and contractor selection guide. Request quotes from local repair technicians and compare prices. Emergency services available for urgent issues.

🛡️ Prevention: Keep Your Aircon Cooling Properly

The best way to avoid why is my aircon not cooling panic is regular maintenance. Here’s a simple prevention schedule:

Read our complete aircon maintenance checklist and service frequency guide. Schedule professional servicing through free inspections and maintenance services.

❓ Frequently Asked Questions About Aircon Not Cooling

✅ Final Thoughts: Don’t Panic—Diagnose First

When your aircon is not cooling, it’s easy to panic and immediately call a technician. But 80% of cooling problems have simple DIY fixes that cost nothing but a few minutes of your time.

Key takeaways for troubleshooting aircon cooling problems:

• Start with the simple stuff: Check remote settings (Cool mode, temperature below room temp), clean the filter, check the breaker. These fix most problems.
• Dirty filters cause 80% of cooling issues: Clean them monthly during summer. It’s free and takes 5 minutes.
• Listen and look for clues: Is the outdoor unit running? Is there ice? Is the airflow weak? These tell you what’s wrong.
• Don’t ignore warning signs: Burning smells, grinding noises, or repeated breaker trips need immediate professional attention.
• Low refrigerant always means a leak: Refrigerant doesn’t get “used up.” If you need gas, you have a leak that must be repaired.
• Regular prevention saves money: Monthly filter cleaning and annual professional servicing prevent 90% of cooling problems.

Your action plan: First, check your remote settings (mode and temperature). Second, clean your filter. Third, check your breaker box. Fourth, inspect the outdoor unit for debris and fan operation. Fifth, if still not cooling after these steps, request quotes from local repair technicians. For emergencies, use our emergency services.