Step 4 : Remove mounting plate from the wall
Unscrew and remove the thermostat's mounting plate from the wall. If necessary, wrap the wires around a pencil to keep them from slipping back behind the wall. Check the instructions that came with the new thermostat. Some models can be programmed before they're wired in place; others must be installed first. If you have the type of thermostat that can be preprogrammed, be sure to first install a fresh 9-volt battery.
Step 5 : Thread the wires
Thread the wires through the base of the new thermostat. Be sure that the base sits flush against the wall and that none of the wires are trapped behind it. Place a torpedo or small level on top of the base and adjust its position until it's perfectly level. Use a sharp pencil to outline the location of the mounting screws on the wall, use the thermostat base as a template.
Step 6 : Fasten the mounting plate to the wall
Remove the base and bore a 3/16-in.-dia. Hole at each screw location. As you're drilling the holes, hold a vacuum cleaner hose up against the wall to catch the drywall dust. Use a hammer to gently tap plastic anchors into the holes. Slip the thermostat's base back into position, thread the wires through the thermostat base, and then secure it to the wall with screws driven into the plastic anchors. Before you tighten the screws, check that the base is level with the torpedo level.
Step 7 : Hook up the wires
If necessary, use the wire stripper to remove about 1/4 in. of insulation from the ends of the wires. Connect the wires to the screw terminals using the masking-tape labels as a guide. The terminals of the new thermostat are marked with the same letters as the old one; just attach the wires to the matching terminals. Also, consult the wiring diagram in the installation manual to make sure everything is properly hooked up. Push the excess wires back inside the wall.
Step 8 : Add the battery
Install a 9-volt battery in the body of the thermostat, then attach the body to the base that's screwed to the wall. In most cases, the thermostat just snaps onto the base.
Step 9 : Program the unit
Turn the electricity back on, then program the thermostat using the pushbutton keypad; be sure to follow the step-by-step instructions in the installation manual. Finally, run a test in both the auto and manual mode to confirm that the furnace and air conditioner turn on and go off, as directed by the thermostat settings.
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