Honeywell RET97B5D User Manual page 11

Installing your thermostat
2 Remove old thermostat faceplate
and leave wires connected.
2a Take a picture of the wire
connections for later reference.
2b If no wire is connected to a
terminal labeled C or no C
terminal exists on the old
thermostat, view the Alternate
Wiring videos at
wifithermostat.com/videos
Important! C wire is required and
is the primary power source for
your thermostat. Without a C wire,
your thermostat will not power up.
If you have an older thermostat with a
sealed mercury tube, turn to page 2
for proper disposal instructions.
C
Terminal
designation
9
MCR33823
69-2805ES—03