Air conditioning (often abbreviated to AC) provides cool, dehumidified air to the passenger cabin.

Air conditioning systems vary from relatively simple systems which blow cold air on demand, through thermostatically controlled systems, to complex split-level, multi-user climate control systems.

Air conditioning is part of a family of systems known as heating, ventilation and air conditioning (HVAC).

Anti-slip regulation (ASR) is another name for traction control, which electronically monitors the vehicle's wheel speeds and reduces engine output it a drive wheel begins to spin.

Anti-stall is a system built into some racing cars to prevent the engine stalling if the driver spins the car.

Anti-stall systems work by detecting when the engine speed is dropping rapidly and automatically disengaging the clutch.

Advance means to alter the timing of an event so that it happens earlier in the combustion cycle.

For instance, advancing the ignition timing in a spark-ignition engine makes the spark happen sooner.

Advance is also the name for the number of degrees of rotation of one event in relation to another, eg 'ignition advance'.

See retard

Anti-lag systems are used in some turbocharged cars to improve performance by preventing the turbo slowing down when the driver shuts the throttle to make a gearchange.

On road cars, recirculation systems can be used which take the high pressure created by the turbocharger's compressor and feeds it back to the turbine. This allows the turbo to continue spinning at high speed.

On competition cars a more aggressive form of anti-lag injects fuel into the exhaust system when the throttle is closed during a gearchange to keep the exhaust flow high, even though the engine is not producing much power. The high exhaust flow keeps the turbocharger spinning rapidly, allowing it to quickly rebuild boost pressure when the throttle is re-opened after the gearchange has been made.