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Car AC not cooling: checks before the garage

Simple checks you can do yourself, and the signs that it needs an AC technician.

17 items · 5 sections · car, mechanic, driver

Start this checklist

Test it properly (4)

  • Set the coldest setting, fan on high and recirculate on
  • Drive for 10 minutes with the windows shut after a hot parking
  • Feel the centre vent: it should be clearly colder than the cabinA cheap thermometer in the vent gives you a number to tell the garage.
  • Note if it is cold when moving and warm when stoppedThat often points to the cooling fan or a blocked condenser.

Under the bonnet, engine off (3)

  • Look through the front grille at the condenserLeaves, bugs and dirt block airflow. Rinse gently with a low-pressure hose.
  • Look for oily patches on AC pipes and jointsOil there usually means a refrigerant leak.
  • Check the AC fuse and relayThe owner manual shows which ones.

Engine running, stay clear of moving parts (3)

  • Turn the AC on and off and listen for a click from the compressorNo click can mean low refrigerant, an electrical fault or a failed clutch.
  • Check the radiator fan comes on with the AC on
  • Listen for squealing or grinding when the AC is onTurn the AC off and get it checked soon: a failing compressor can damage the belt.

Inside the car (4)

  • Check the cabin filterA dirty one means weak airflow. Change it as the manual says, often once a year.
  • Weak airflow on every fan speed: suspect the filter or the blower motor
  • Air cold on one side only: tell the garageCould be the blend door or dual-zone controls.
  • Musty smell: run the fan with the AC off for the last few minutes of a drive

Before you pay (3)

  • Skip DIY refrigerant cans if you suspect a leakToo much refrigerant can hurt cooling, and a leak will just lose it again.
  • Ask for a leak test, not only a regas
  • Ask for the pressure readings and a written estimate

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