Air Conditioner cutout

2000 Tacoma V6 177K
So recently the air conditioner will work fine for 20 or 30 minutes then just start blowing ambient temp air.
Next day it will work fine.
Not that I am going to work on this myself but I do like to have some idea of what might be failing before I take it to the shop.
Any thoughts?
Thanks.

 

It needs re- charged,that's common when refrigerant is low.

 

I had an issue similar. The ac would kick on for a few and then off. I thought it was a refrigerant issue, but that was actually fine. Turned out to be a faulty thermistor in the evap box. Unfortunately, this part is installed in the box and cannot be reached without dismantling everything. I ended up jumping the wire so the ac would just run. It's blowing freezing cold. I just have to be careful that the evap coil doesn't freeze over. Been working fine for over a year now.