Driver Knowledge Tests

Tips for getting car air conditioning to work better

When you get in your vehicle and it’s hot, run the air conditioning immediately, but leave the doors or windows open until the temperature inside the cabin normalises to the temperature outside the cabin. This means that air being passed over the evaporator will now be the same temperature as the air outside the cabin, giving the aircon an easier job.

At the start, set your air conditioning to maximum fan, minimum temperature and recirculating the air. This moves the greatest volume of air and recirculates it within the cabin to cool things down more rapidly. Once the temperature is comfortable, switch the recirculate off and select a lower fan speed. Lower fan speeds produce colder air from the system.

Run the air conditioning using outside air (i.e. not recirculate) frequently to avoid bad smells through the fans

Don’t try to service your air conditioning if you don’t know what you are doing. The system is under high pressure and the refrigerant is environmentally hazardous.

Better performance can be maintained if you wash or blow out the condenser coil and radiator a couple of times per year.

Air-conditioned air is very dry, so use the aircon when you need to demist your windscreen. Also, if you have got in your vehicle after being in the rain, use the air conditioning to prevent evaporation from your clothing and body steaming up the windows.

Be careful not to run the air conditioning hot for a long period of time otherwise it can make you sleepy.

Air conditioning makes the air very dry in your vehicle which can make your eyes itchy.

Does air conditioning affect your vehicle’s performance?

As the air conditioning needs power to run, it takes this power from the engine. Generally, it takes around 3kW or 4 horsepower to run the unit. Air conditioning uses more fuel, so use it sparingly.

The compressor clutch engages and disengages as is required to keep the system as cool as is required. In some vehicles you will feel it kicking in when travelling at a constant speed because your vehicle will begin to lose speed as power is diverted from the wheels to the air conditioning. This is because when travelling at a constant speed, your vehicle doesn’t need much power – just enough to overcome the resistance from the wind, tyres and the internal friction from the engine and drivetrain.

When the air conditioning is running, acceleration will be slower.

An air conditioning unit is heavy, weighing in at over 15kg, so you will also be paying that weight penalty with your fuel use.

It’s usually more economical to drive with your windows open than run the aircon, even thought windows open creates more drag. The faster you go, the more drag is created, so eventually open windows will become less efficient than aircon, but it depends on the vehicle at which speed this happens.

What are common problems with air conditioning units?

  • The condenser and evaporator can get dirty which reduces their effectiveness.
  • The cab filter can become clogged, reducing airflow.
  • Aircon units periodically might need to be regassed to replace old gas or if there has been a leak.
  • The air conditioning pump is driven off the engine via a belt. Sometimes this can come loose, leading to a squealing sound from under the bonnet. A mechanic can adjust it.
  • Debris can get trapped in the vents.

Air conditioning units should be checked and serviced every couple of years, but most people leave theirs until it stops blowing cold air.

Water will drip from your air conditioning unit when the weather is humid and you stop your car after using the unit. This is because in summer, the aircon unit has to work very hard and it can ice over. The water is the ice melting. This will form a puddle under the engine, but it’s nothing to worry about.

What is regassing your aircon?

Over time, your air conditioning may become less effective and eventually it won’t blow cold any more. Your air conditioning system is a closed system therefore if everything is working well, it shouldn’t need topping up, but the refrigerant can lose its effectiveness.

Regassing is removing the old refrigerant and replacing it with new, more effective refrigerant.

However, if the refrigerant is leaking, you will need to find the leak then regas the system.

Any type of work on the aircon unit is best left to a professional with the right tools, but you can purchases kits and tools to do this work (just be careful you don’t create a problem that is more expensive to fix than the initial regassing was going to be). Regassing the system will take around an hour for a reputable mechanic.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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