Step 2. Remove the old thermostat
Turn off power to the heating/cooling system, either at the
furnace or at the fuse/circuit breaker panel.
Remove the cover of your old thermostat (Fig. 2).
Unscrew and remove the old thermostat's mounting plate from
the wall, but do not disconnect the wires.
Inspect the old thermostat wiring. If the wiring meets any of
the following conditions, see the special wiring
instructions on page 9.
• The old thermostat is a clock thermostat with wires attached
to the C or C1 terminals.
• The old thermostat has 6 or more wires, excluding wires
attached to C or C1 terminals.
• The old thermostat has 3 wires.
• There are 5 wires connected to the old thermostat.
• There are extra wires that are not connected to the old
Using the enclosed labels, mark the wires with the letter of the
terminal that it is attached to on the old thermostat (Fig. 3). Do
not label the wires by color.
If the labels do not match the letters on the old thermostat
terminals, see the wiring cross reference table on page 10.
Disconnect the wires from the old thermostat and wrap the
wires around a pencil to keep them from falling back into the
Note: Remember, if your old thermostat contains mercury, you
must recycle it. See page 2 for more recycling information.
Check your progress
Your wall should now look like Fig. 4.