2009 Honda Civic Sdn - AC fades away

My air conditioner stops giving out cool air after a little while of driving. I noticed it last when driving up a steep hill but this issue tends to happen when driving on regular roads.
I checked the refrigerant pressure and it was just slightly below requirements. What could this issue be?

first add refridgerant to proper level. if that doesnt help you can research online for the proper air gap of your clutch.then check with a feeler gauge to see if the gap is too big. if it is, there is a plate in front of your clutch held on by a couple of bolts. take out bolts. there will be a few different thickness’s of spacers. they look like washers. remove one that will get it to the correct gap. also clean the back of the plate. the compressor acts like a magnet pulling in the plate. when in gaged the compressor makes your cold air to put it simply. if the gap is to big the compressor wont in gage properly or will work for a little while and stop. i had this happen in my pickup and if fixed the problem. of coarse this is one of many things that could be wrong.