Sounds like the unit is freezing up..turn it off and see if ice drips off the evaporator....the fact that it is good in the morning and eventually stops blowing cool air sure points to icing up.
Stuart and Stella Denning
2016 Entegra Aspire 42RBQ
The 3 Bulldogs (Daisy, Sylvie and Stashie)
2018 Equinox Diesel (TOAD)