or disconnects. Remove any existing wallplate or sub-
base from wall. To avoid miswiring later, label each
wire color with the letter or number on the wiring termi-
nal as the wire is removed.
If this control is replacing a control that contains
mercury in a sealed tube, do not place your old control in
the trash. Contact your local waste management author-
ity for instructions regarding recycling and the proper
disposal of your old control.
Run cable to a hole at the selected wall location for the
thermostat, and pull about 3 in. [76 mm] of wire through
the opening. Color-coded, 18-gauge thermostat cable with
at least one conductor for each wiring terminal is recom-
mended. Good service practice recommends selecting
cable with one or two more conductors than the immedi-
ate application requires.
If you have any questions, call Honeywell Inc. at 1-
The T8624 Thermostats will replace most heating/
cooling system thermostats. As long as ac power is
continuously available to the transformer, the thermostat
will be compatible with any low-volt control system.
IMPORTANT: Before mounting, set the system switch
IMPORTANT: The T8624 requires an additional con-
ductor to transformer common to provide continu-
ous 24V power for thermostat operation.
to the OFF position.
NOTE: The subbase does not require leveling for proper
operation, but only for appearance.
WHEN INSTALLING THIS PRODUCT…
. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazardous
Fig. 3—Removing thermostat from subbase.
. Check the ratings given on the product to make
sure the product is suitable for your application.
. Installer must be a trained, experienced service
. Allow thermostat to warm to room temperature
. After installation is complete, check out product
operation as provided in these instructions.
HEAT AUTO COOL
Disconnect power supply to prevent electrical
shock or equipment damage.
Install thermostat and subbase about 5 ft [1.5m] above
the floor in an area with good air circulation at room
Do not install thermostat where it may be affected by:
drafts or dead spots behind doors, in corners or
hot or cold air from ducts.
radiant heat from sun or appliances.
concealed pipes and chimneys.
unheated (uncooled) areas such as an outside wall
behind the thermostat.
Remove thermostat from subbase (Fig. 3).
Mount the subbase directly onto the wall with the
screws and anchors included. If drywall construction,
use plastic anchors. Use the subbase as a template, and
with a pencil, mark the two mounting screw positions
3/16 in. bit to drill holes for anchors. Gently tap anchors
into holes until they are flush with the wall surface.
Thread wires through the center opening of the subbase.
Then mount the subbase using the two screws provided.
Gently tighten the screws, level the top surface of the
subbase, and securely tighten the screws.
REPLACING AN EXISTING THERMOSTAT
Turn off thermostat power at furnace or boiler. A two-
transformer system may require turning off two switches