Posted by Grant Richardson, 19th May, 2015
Either. But they mean different things.
In some languages (such as, Italian or Cantonese), you might ask your friend to “Please open the aircon” when you feel too hot or “Please close the aircon”, when you feel too cold.
Be careful! In English, if you feel hot, you must say “Please switch on the aircon” or “Please turn on the aircon”. If you feel cold, you should say “Please switch off the aircon” or “Please turn off the aircon”.
You say “open the aircon” if you want to see inside to clean it or if you want to fix it. And, “close the aircon” when this job is done.
Imagine how your friend would feel if you asked him/her to “Please open the light” (to make the room brighter). They will probably think you asked them to do something impractical and dangerous.
There is no difference in meaning between “switch on” and “turn on”, and no difference between “switch off” and “turn off”.
You also use these phrasal verbs “switch on/off” and “turn on/off” for almost any other electrical device or equipment such as a light, an exhaust fan, the TV.
On the other hand, some things you CAN ask your friend to “Please open” include “the window”, “the door”, “the fridge”, or “the rubbish bin” (which is called “the trash can” in American English); basically, anything with a door, handle, or cover.
In English, you don’t say
Please stop the aircon
unless it is falling off the wall or rolling down a hill (in which cases, it is probably too late anyway).