2012 Nissan Altima coupe 2.5. The AC stops blowing after 20min

after driving for 20 min or so the AC stops blowing.  I know the big line
,suction? under the hood is freezing solid.  ive changed the expansion valve,
the blower motor, and the interior climate control and no changes.  the
interior cabin filter has been changed as well, and sprayed cleaner on what
looked like an already clean evap. coil.  refrig levels are correct, no leaks,
compressor seems fine.  Once the line defrosts, it blows cold again,  then
freezes and obviously stops allowing air through the evap coil and into the
cabin..  what else can be causing this problem?  compressor control valve?
ambient temp control sensor?  any help!! im lost and broke.