Why is my air conditioner running but blowing warm air?

A split system blowing warm air usually indicates restricted airflow, an incorrect remote setting, or lost refrigerant. Verify the remote is set to Cool mode rather than Fan or Dry, and ensure the setpoint is below room temperature. Wash blocked nylon filters and clear garden debris from the outdoor condenser coil. If airflow remains warm, suspect a refrigerant leak or compressor failure.

Can I regas my own split system air conditioner in Australia?

No, it is illegal to purchase, handle, or decant scheduled refrigerants in Australia without an ARC licence under the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989. Air conditioners operate on closed systems that do not consume gas. Low pressure indicates a physical leak requiring licensed nitrogen pressure testing, flare repair, evacuation below 500 microns, and scale weigh-in.

What temperature drop should a split system produce across the indoor coil?

A properly functioning split system should achieve a temperature drop between 8°C and 12°C across the indoor unit. Measure this by subtracting the supply air temperature at the discharge louvre from the return air temperature entering the top grille after 15 minutes of continuous cooling. A delta T under 6°C indicates airflow restriction, dirty coils, or undercharge.

Why is ice forming on my split system indoor unit or brass valves?

Ice forms when restricted airflow or low refrigerant reduces the evaporator coil pressure, dropping its surface temperature below freezing. Severely choked return air filters, a fouled indoor cross-flow fan, or an R32/R410A leak starve the coil of heat, causing condensed moisture to freeze solid. Turn the system off immediately to thaw the coil and prevent liquid slugging damage to the compressor.

How do I tell if the outdoor compressor is actually running?

Determine if the compressor is running by listening for a distinct low-frequency hum and observing the outdoor fan operation. In inverter systems, the compressor ramps up gradually rather than kicking in with a loud click. If the outdoor fan spins but discharges cool ambient air instead of warm, rejected heat, the compressor has likely tripped on thermal overload or suffered an inverter board failure.

How often should split system air conditioner filters be cleaned in Australia?

Split system dust filters should be cleaned every two to four weeks during high-use summer and winter months, and at least quarterly otherwise. Clogged mesh filters starve the indoor coil of air, cutting cooling performance, increasing power consumption, and risking condensate overflow. Wash them under lukewarm water, air dry in the shade, and vacuum the coil face.

Why is my split system running but not cooling?

Split system running but not cooling? Diagnose dirty filters, choked condenser coils, low refrigerant, or compressor issues with this Australian trade guide.

Quick answer

A split system that runs without cooling is typically caused by choked indoor air filters, blocked outdoor condenser coils, or a refrigerant leak. A healthy system delivers an 8°C to 12°C temperature drop across the indoor unit. If cleaning the filters and outdoor coil fails to restore cold air, contact an ARC-licensed technician.

Skill level: All levels
Time: 4 min read
Trade: HVAC & Refrigeration
Updated: 14 November 2026

Tools you will need

Fieldpiece SMAN480V - 4-Port Digital Refrigeration Manifold
Testo 405i - Wireless Thermal Anemometer
Fluke 62 MAX+ - Handheld Infrared Laser Thermometer
Navac NP4DP - 4 CFM Dual-Stage Vacuum Pump
Kärcher K2 Follow Me - Low Pressure Cordless Coil Washer
Advanced Engineering StayClean - Evaporator Coil Cleaner Spray
Inficon Wey-TEK HD - Wireless Refrigerant Charging Scale
Fieldpiece DR82 - Infrared Refrigerant Leak Detector

The short answer

Most "not cooling" calls come down to airflow, not gas. Dirty indoor filters and a leaf-choked or sun-baked outdoor unit strangle the system so it runs hard and delivers barely-cool air.

Before anything else, rule out the basics: filters cleaned, outdoor coil clear, mode set to Cool (not Fan or Auto), and the setpoint several degrees below the room. Confirm the outdoor fan and compressor actually start.

What it depends on

Whether air comes out at all -- no airflow points to the indoor fan or filters; airflow that is not cold points to refrigerant or the compressor.

Outdoor unit condition -- a unit in full sun, boxed in, or clogged with leaves will underperform no matter how well the indoor head is set.

Age and servicing history -- refrigerant does not "run out" normally; low gas means a leak, which needs finding and fixing, not just topping up.

Whether it ices up -- ice on the indoor coil or outdoor pipes points to low airflow or low refrigerant.

Your next step

Filter cleaning and clearing the outdoor unit are operator jobs and fix a surprising share of cases. Anything involving refrigerant -- leak detection, regas, compressor faults -- must be done by a technician holding an ARC refrigerant handling licence; it is illegal to handle refrigerant without one. See more air-conditioning and HVAC guides.

Frequently asked questions

Why is my air conditioner running but blowing warm air?: A split system blowing warm air usually indicates restricted airflow, an incorrect remote setting, or lost refrigerant. Verify the remote is set to Cool mode rather than Fan or Dry, and ensure the setpoint is below room temperature. Wash blocked nylon filters and clear garden debris from the outdoor condenser coil. If airflow remains warm, suspect a refrigerant leak or compressor failure.
Can I regas my own split system air conditioner in Australia?: No, it is illegal to purchase, handle, or decant scheduled refrigerants in Australia without an ARC licence under the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989. Air conditioners operate on closed systems that do not consume gas. Low pressure indicates a physical leak requiring licensed nitrogen pressure testing, flare repair, evacuation below 500 microns, and scale weigh-in.
What temperature drop should a split system produce across the indoor coil?: A properly functioning split system should achieve a temperature drop between 8°C and 12°C across the indoor unit. Measure this by subtracting the supply air temperature at the discharge louvre from the return air temperature entering the top grille after 15 minutes of continuous cooling. A delta T under 6°C indicates airflow restriction, dirty coils, or undercharge.
Why is ice forming on my split system indoor unit or brass valves?: Ice forms when restricted airflow or low refrigerant reduces the evaporator coil pressure, dropping its surface temperature below freezing. Severely choked return air filters, a fouled indoor cross-flow fan, or an R32/R410A leak starve the coil of heat, causing condensed moisture to freeze solid. Turn the system off immediately to thaw the coil and prevent liquid slugging damage to the compressor.
How do I tell if the outdoor compressor is actually running?: Determine if the compressor is running by listening for a distinct low-frequency hum and observing the outdoor fan operation. In inverter systems, the compressor ramps up gradually rather than kicking in with a loud click. If the outdoor fan spins but discharges cool ambient air instead of warm, rejected heat, the compressor has likely tripped on thermal overload or suffered an inverter board failure.
How often should split system air conditioner filters be cleaned in Australia?: Split system dust filters should be cleaned every two to four weeks during high-use summer and winter months, and at least quarterly otherwise. Clogged mesh filters starve the indoor coil of air, cutting cooling performance, increasing power consumption, and risking condensate overflow. Wash them under lukewarm water, air dry in the shade, and vacuum the coil face.

Written by Frosty, the HVAC & Refrigeration specialist at QLD.Tools.