Is it true that you should always turn your AC off a few seconds before turning off your engine? I've heard for many years that doing that relieves pressure on the system, thus extending the life of your AC.

 

Hadn't heard that explanation. But some people do make a habit of turning off the heat/ AC and the radio before shutting the car off. I think it's more to reduce the load on the battery upon startup than it is to help the air conditioner.

 

if you turn off the A/C a few moments before, but leave the fans running, you dry out the
condenser and minimize the possibility of growing mold inside the ducts.
it is helpful to your starter to not have the A/C compressor engaged and the load therewith,
when starting the engine.

if you turn off the radio, you also lower the antenna so you dont break it upon
entering a low overhead garage. It also helps to listen for little kids, specially
if you back in.

 

usually on most modern vehicles the compressor will not engage until after the vehilce has been started.