It sounds to me like your evaporator core is freezing up, which is something the system compensates for with a drain (so water condensing on the evaporator core can drain). 1st thing I'd check is to see if the drain is clogged.
If it is not clogged, I would check with the vendor and find out how their system prevents core freeze, they may pass coolant continuously through the heater core and have a hot air bleed somewhere that keeps the evaporator from icing up. There might be a fail in there somewhere.
Hope that helps.
I did find a bad crimp in one of the drain hoses, so I replaced the plastic with a rubber hose. Then the other plastic hose came lose and water drained into the floor board. I now have replaced that plastic drain hose with a rubber one. Have not used the AC since.
