not sure what it is, but every year i have to add freon on my ac. my dad did it last year and it worked great all summer. my dad told me to just add freon and once its full it will stop taking. the autoshop here i go to tells me i have to use a gauge and fill it to a certain pressure. i filled my ac to the pressure they told me and the ac is cooler, but not near as cold as it was last year. and i know the ac will take more freon, so should i add more until it stops taking it or keep it at a certain pressure?