Category: Air conditioning

  • What are the common car air conditioning problems and what should I do?

    Quick answer

    The most common problems are warm air (often a refrigerant leak, a compressor that isn’t engaging or a fan that isn’t running), weak airflow (often a blocked cabin filter or a failed blower resistor), and musty smells (mould on the evaporator). You can check the cabin filter, fuses, fans and the condenser yourself. Anything involving the refrigerant is a job for a trained technician: handling R134a, the gas in most older cars, needs an Australian Refrigeration Council (ARC) licence, and leaks must be repaired before the system is regassed.

    Is this a DIY job?

    • Difficulty: Easy for the basic checks below; Pro for anything involving refrigerant
    • Time: 15 to 30 minutes for the checks
    • Tools: owner’s manual, torch, garden hose with a gentle spray (for the condenser)
    • Skills: none for the checks

    In Australia, anyone who handles R134a in a car air conditioner needs a refrigerant handling licence from the ARC. That includes topping up, regassing, recovering gas and opening the system. Many newer cars use R1234yf. In pure form it isn’t covered by the federal licence scheme, but it’s mildly flammable and needs dedicated equipment, so it’s still a job for a trained technician. The checks below don’t touch the refrigerant.

    How car air conditioning works

    How car air conditioning works: the refrigerant loop The compressor pumps hot high-pressure refrigerant gas to the condenser at the front of the car, where it gives off heat and becomes liquid. A receiver-drier or accumulator removes moisture. The expansion valve or orifice tube drops the pressure so the refrigerant becomes very cold. In the evaporator inside the dash, it absorbs heat from cabin air pushed through by the blower fan, then returns to the compressor as low-pressure gas. Condensed water drains under the car. How car air conditioning works ENGINE BAY FIREWALL AND DASH 2. Condenser front of car: heat out, gas turns to liquid 1. Compressor belt-driven (or electric high-voltage on hybrids/EVs) Receiver-drier removes moisture* 3. Expansion valve or orifice tube: pressure drops, gets very cold 4. Evaporator absorbs heat from cabin air Blower fan through cabin filter, across evaporator hot, high-pressure gas liquid cold, low pressure low-pressure gas back Cold air to vents Condensed water drains under the car *Orifice-tube systems use an accumulator on the return side instead. It’s a sealed system. If the refrigerant is low, there’s a leak. Refrigerant work is for a licensed technician (ARC licence for R134a). Leaks must be repaired before regassing.
    Car air conditioning refrigerant loop: compressor, condenser, expansion device and evaporator

    The compressor pumps refrigerant around a sealed loop. At the condenser (in front of the radiator) the refrigerant gives off heat to the outside air. It then passes through an expansion valve or orifice tube, where its pressure drops and it gets very cold. In the evaporator (inside the dash), it absorbs heat from the cabin air that the blower fan pushes through it. Moisture from the air condenses on the cold evaporator and drains out under the car.

    Step by step: checks you can do

    1. Check the settings. A/C button on, temperature at coldest, fan on a medium speed, recirculate on for a hot car. Make sure the system isn’t set to heat or demist only.
    2. Listen for the compressor. With the engine idling and the bonnet up, have a helper switch the A/C on and off. On most engines with a belt-driven compressor you’ll hear a click and see the centre of the compressor pulley start spinning. Keep hands, hair and clothing well clear of the belt and fan. No click can mean low refrigerant (the system protects itself), a fuse, a relay or a sensor fault.
    3. Check the condenser fan. With the A/C on, the electric fan in front of the radiator should run on most cars. If it doesn’t, the A/C will struggle, especially when stopped in traffic.
    4. Look at the condenser. Through the front grille, check for leaves, bugs, mud or bent fins. A gentle rinse from behind with a hose (low pressure) can help. Don’t use a high-pressure washer on the fins.
    5. Check the cabin air filter. It’s usually behind the glovebox. A blocked filter causes weak airflow and smells. Replace it if it’s dirty.
    6. Check the blower speeds. If the fan only works on its highest setting, the blower resistor (or its connector) has usually failed.
    7. Check the fuses and relays. Your owner’s manual shows the A/C, blower and condenser fan fuses. (see How do I check and replace a blown fuse?)
    8. Note what you’ve found. Warm air, noise, smell, when it happens (only at idle? after a while?). This helps the technician find the fault faster.
    9. Book a licensed technician for anything else. If the compressor won’t engage, air stays warm, or you suspect a leak, it needs testing with proper gauges and leak detection. A licensed technician must find and repair any leak before regassing.

    Specs table

    Common problems and likely causes

    Symptom Common causes What you can do
    Warm or barely cool air Refrigerant leak (low charge), compressor not engaging, condenser fan not running, blocked condenser, blend door stuck on heat Check settings, fans, condenser and fuses; then book a licensed technician
    Cold at first, then warm Low charge, evaporator icing, compressor cutting out Licensed technician
    Weak airflow Blocked cabin filter, failed blower motor, debris in the air intake Replace cabin filter; clear the intake below the windscreen
    Fan only works on high Failed blower resistor or burnt connector Replace resistor and check the connector
    Musty or mouldy smell Mould or bacteria on the evaporator; blocked drain; dirty filter Replace cabin filter; evaporator cleaning by a workshop
    Sweet smell, foggy windscreen Possible coolant leak from the heater core Get it checked soon; coolant fumes shouldn’t be breathed
    Water in the front footwell Blocked evaporator drain Have the drain cleared
    Water dripping under the car Normal condensation from the evaporator Nothing, if it’s clear water and stops after the car is off
    Rattling, grinding or squealing with A/C on Compressor clutch or bearing, belt, blower fan debris Book in; stop using A/C if the noise is loud
    Clicking behind the dash Blend or mode door actuator Book in

    Refrigerant type: Check the label under the bonnet. Older cars use R134a; many newer cars use R1234yf. They must not be mixed, a system shouldn’t be converted from one to the other, and only the type on the label should be used. R1234yf is classed as mildly flammable.

    What you’ll need

    • cabin air filter (vehicle-specific)
    • blower motor resistor (vehicle-specific, if the fan only works on high)
    • blade fuses
    • automotive relay

    When to call an auto electrician

    • Any job that involves the refrigerant: topping up, regassing, leak testing, replacing hoses, the compressor, condenser, evaporator or valves. Choose a technician who holds an ARC refrigerant handling licence. It’s illegal to regas without repairing existing leaks, and illegal to vent refrigerant to the air.
    • Hybrids and EVs. Many use an electric A/C compressor powered by the high-voltage battery. That’s professional-only work: never touch orange cables.
    • The compressor clutch, condenser fan or blower don’t work and the fuses are fine.
    • A sweet smell, steam from the vents, or a greasy film on the inside of the windscreen. These can point to a heater core leak.
    • The A/C makes loud grinding or squealing noises.

    Avoid DIY “regas” cans and so-called drop-in replacement gases. Handling refrigerant without a licence is an offence, some alternative gases are flammable, and the wrong gas or oil can damage the system and contaminate workshop equipment.

    Need an auto electrician? Find local auto electricians and mobile services in your city.

    Find an auto electrician near you

    Related questions

    Q: Can I regas my car air conditioning myself? A: No. In Australia, handling R134a needs an ARC licence, newer R1234yf systems need dedicated equipment, and any leak must be repaired before the system is regassed.

    Q: How often does car air con need a regas? A: A car A/C system is sealed, so it shouldn’t need regular regassing. If it’s low, there’s a leak. Many workshops suggest a check every year or two, ideally before summer.

    Q: Why does my air con smell musty? A: Mould and bacteria grow on the damp evaporator. Replacing the cabin filter helps, and a workshop can clean the evaporator.

    Q: Should I run the air con in winter? A: Running it every few weeks circulates the oil in the refrigerant, which helps keep the seals from drying out. Many cars also run the A/C automatically when you demist.

    Q: Is water dripping under my car normal? A: Clear water dripping from under the front of the car when the A/C has been on is normal condensation. Water inside the car, or coloured or oily fluid, isn’t.

    Sources

    1. Australian Refrigeration Council, “What work requires a refrigerant handling licence?” – licence needed for decanting refrigerant and for servicing equipment. https://arctick.org/information/report-a-breach-relating-to-regulated-refrigerants/what-work-requires-a-refrigerant-handling-licence/ (checked October 2026)
    2. Australian Refrigeration Council, “Fact sheet 4: How to obtain an automotive air conditioning licence” – licence covers passenger and commercial vehicle A/C; handling refrigerant without a licence is an offence. https://www.arctick.org/media/1108/fact-sheet-4-automotive-air-conditioning-licence.pdf (checked October 2026)
    3. Australian Refrigeration Council, consumer handout for car air conditioning – regassing without repairing leaks is illegal; discharging refrigerant is illegal. https://www.arctick.org/media/42727/arc5919a_racautohandouts_a5_auto_web.pdf (checked October 2026)
    4. Australian Refrigeration Council, Fact sheet 17, “The Australian automotive code of practice 2008” – mandatory practices for licensed technicians; discharging refrigerant is illegal. https://www.arctick.org/media/1188/arc_fact-sheet_17.pdf (checked October 2026)
    5. Australian Refrigeration Council, “Emerging automotive refrigerants” – R134a needs a licence; pure R1234yf isn’t regulated under the federal scheme. https://www.arctick.org/information/autogas (checked October 2026)
    6. Australian Refrigeration Council, “Automotive gas booklet” (2023) – R1234yf is A2L mildly flammable; licence needed if a blend may be present; R134a systems shouldn’t be converted. https://www.arctick.org/media/29049/auto-gas-booklet_2023.pdf (checked October 2026)
    7. Natrad, “Everything you need to know about car aircon re-gassing” – common causes of leaks, alternative gases can be flammable, run A/C in winter, check every 1 to 2 years. https://natrad.com.au/info-advice/how-often-does-your-cars-aircon-need-re-gassing/ (checked October 2026)