the compressor on my 2012 sentra will not come on. The fuse is good ,the ac switch lights up?

Check freon,may be it leaked out.

yes its full, i serviced the air condioner at vo-tec school.

Ok ,check ac relay?

have looked for relay under hood and dash unable to find.called parts store for relay they could not find one for a 2012 nissan.

I just checked you are right,there is no,ac relay on your car,the relay was replaced on the newer model,s with a ac Expansion Valve,if ac is full of freon and you have power at ac compressor.this valve may be your problem,it want let your freon circulate nor activate your compressor.

there is no power at the compressor. thanks

low pressure cut off switch. check to see if has juice b/f switch, you can jump lpcos momentarily and see if compressor clutch kicks on.