Air conditioning problem
Aircon Not Cooling? Causes and What to Check
Aircon runs but blows warm air - often a dirty filter, thermostat, blocked coils or low refrigerant.
Request Free QuotesQuick answerAircon runs but blows warm air - often a dirty filter, thermostat, blocked coils or low refrigerant.
What this problem usually means
An air conditioner that runs but blows warm air is one of the most common summer complaints in Johannesburg homes, and the cause is often something simple - a faulty thermostat, blocked filter, dirty coils or low refrigerant. On this platform you can work out the likely cause before booking a visit, then compare quotes from independent Johannesburg technicians. Some checks are safe for owners to do themselves, while others need a certified technician for safety and warranty reasons. This platform does not perform repairs itself; it simply helps you find qualified technicians and compare options.
Quick Facts & Key Takeaways
- Warm air from a running unit splits into two groups: airflow and thermostat faults you can often sort yourself, and sealed-circuit faults like low refrigerant or a failed capacitor that need a technician - so rule out the cheap DIY causes first.
- Owner-safe checks come first: confirm power at the breaker, set the thermostat to cool below room temperature with fresh batteries, and clean or replace the filter.
- Dirty coils and blocked vents reduce heat transfer, so keep clear vents indoors and clearance around the outdoor condenser.
- Low refrigerant means a leak in the sealed circuit, so a technician must pressure-test and regas the system - ask them to confirm SAQCC Gas registration, since refrigerant handling is regulated in South Africa.
- Failed capacitors or a worn compressor need a qualified repair technician, and a yearly service before summer prevents most no-cooling call-outs.
Start here
Signs & symptoms
- Unit runs but blows warm air across the room
- Humming compressor that won't start, or a stalled fan
- Hissing sound or ice build-up on the evaporator coil
- Oily residue around pipe joints and bubbling noises near the unit
- Rattling or grinding noise with reduced airflow
- Unit cycles rapidly or runs constantly but still fails to cool
What may be happening
Likely causes
- Blocked or clogged air filter restricting airflow, which can also make the unit trip the breaker
- Thermostat set incorrectly or needing fresh batteries or reprogramming
- Dirty condenser, clogged coils or blocked fins reducing heat transfer
- Failed capacitor or worn compressor (needs professional diagnosis)
- Low refrigerant from a leak in the sealed circuit, which a professional aircon regas puts right
- Blocked vents, a clogged condensate drain, or incorrect unit sizing
Repair path
How it's fixed
Work through safe owner checks first, then use a qualified technician where the system needs testing or repair.
- Owner checks: confirm power at the breaker, set the thermostat to cool below room temperature and replace its batteries
- Inspect filters monthly and clean or replace them if dirty, since a clogged filter can freeze the coil and leak water indoors
- Clear indoor vents and keep clearance around the outdoor condenser so it can breathe, and if simple checks don't help, work through our aircon problems guide to narrow the fault
- A qualified repair technician diagnoses and replaces failed capacitors or a worn compressor
- A technician performs a pressure test, locates leaks and safely recharges refrigerant
- Book a yearly professional service before summer covering coils, refrigerant levels and electrical checks
What to look for
Can I fix this myself?
Owners can safely check the breaker, thermostat, filters and clear vents, but any work on pressurised refrigerant lines legally requires a certified SAQCC Gas-registered technician, and capacitor or compressor repairs should be left to a qualified technician.
The service that fixes this
Fix it & related issues
Services, tools and related air conditioning problems.
Aircon Not Cooling - Common Questions
Common questions about air conditioning pricing, the quote request process, and how this platform works.
Why is my aircon not blowing cold air?
Start with simple checks: confirm the thermostat is set to cool and lower than room temperature, check the fan setting, and clean or replace clogged filters. Blocked vents, dirty coils or a failed fan motor can also reduce cooling, while a refrigerant leak, compressor or capacitor fault will need a certified technician to diagnose and repair.
Can a dirty filter make my system stop cooling?
Yes. A heavily soiled filter restricts airflow, causing the evaporator coil to ice up and reducing the temperature drop. Cleaning or replacing filters regularly improves efficiency and often restores proper cooling without a service call.
How do I know if there's a refrigerant leak?
Signs of low refrigerant include reduced cooling, longer run times, hissing sounds, oily stains near connections and frozen evaporator coils. Refrigerant handling requires a certified technician who will pressure-test the system, locate leaks and restore the correct charge - never try to top it up yourself.
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