Possible that the vent control is blocked or is being turned off. you will need to check this out or it can be fault within the blower, the vent control or a physical block.
The loss of cooling can be due to many reasons and it can be related to clogged evaporator, faulty, compressor, low gas or faulty fan/condensor.
I think you must take consensus before any part is changed, check all the controls, check fan or it might need a resetting of the blower/evaporator unit.