Warm air from the vents usually starts at the coil, not the thermostat
When the air coming out of the vents turns lukewarm, most homeowners blame the thermostat. In a Cypress house the real culprit is more often the evaporator coil, the refrigerant circuit or a weak capacitor. Attics in this area get brutally hot, and a system that runs most of the day from May through October gives every weak part a chance to fail.
Ice on the line set tells a different story. Frost on the insulated copper line outside, or on the coil inside, usually means low airflow or a charge problem, and running the system longer only makes it worse. Short cycling, where the outdoor unit clicks on and off every few minutes, points toward a failing contactor, a tripped safety switch or a unit that is too big for the house.