A common DFW renovation is enclosing an old covered patio to create a "Sunroom" or "Florida Room." The contractor inevitably taps a single 6-inch flex duct off the main house AC and runs a vent to the new room. By July, the room is completely uninhabitable.
The "Supply-Only" Disaster
An air conditioner is a closed-loop system. It must suck hot air out of a room (Return) at the exact same velocity it pushes cold air in (Supply). If a contractor adds a supply vent to a sunroom but fails to add a massive return vent, the room becomes positively pressurized. The cold air physically cannot push its way into the room because the room is already full of hot, trapped air.
Most patio roofs are uninsulated flat decks originally designed to simply block rain. When enclosed, that flat roof acts as a massive thermal radiator, pumping 130°F directly into the room from above, completely overwhelming the single 6-inch AC vent.
The only reliable way to salvage an enclosed patio is to completely sever it from the central house AC. Insulate the flat roof cavity with dense-pack cellulose or foam, and mount a dedicated Ductless Mini-Split head on the wall. The mini-split acts as its own self-contained micro-climate, handling both supply and return seamlessly.