TV's "48 Hours" premiered this day in 1988. A programming breakthrough, it focused on a two- day period. Setback thermostats represent a programming breakthrough, too, with the capability to deliver preprogrammed heat and cooling commands for days, weeks and even months at a time. But, as high-tech as these instruments are, they're only as good as their installation. And improper placement or poor workmanship defeats even the most sophisticated units. While day-to-day operation is complex, their installation is quite simple and basic. First, when removing the old unit, spread wires apart so they don't slip and fall down inside the wall. Before installing a new unit, seal the hole with foam insulation and caulk to prevent drafts that could affect operation of a new thermostat. Also, a level installation is needed. Then, grab the directions, check the news, to see what the weather's going to be. Then set it (for 48 hours or more ahead) and forget it. And that's the On The House tip for today.