T8621A,C,D, CHRONOTHERM III
FUEL SAVER THERMOSTATS
These thermostats provide energy saving control for a
4 Vac heating/cooling system as indicated in Table 1, and
necessary. Cycle rates are adjustable for highest stage of
are powered direct from the control transformer.
Fan operation option switch is included on SUPER
TRADELINE model to select fan operation for electric heat
12/24 hour clock conversion and °C/°F conversion is
available on some models only.
As long as thermostat is continuously powered, the
thermostat will be compatible with any control system.
These models include a SYSTEM LED, which is on
and cool anticipation is fixed in all models; no adjustment is
TABLE 1—THERMOSTAT MODELS.
aSUPER TRADELINE model.
WHEN INSTALLING THIS PRODUCT…
. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazardous
IF NEW INSTALLATION
Run cable to a hole at the selected wall location, and pull
about 3 in. [76 mm] of wire through the opening. Color-
coded, 18 gauge thermostat cable with one conductor for
each wiring terminal is recommended. Good service prac-
tice recommends selecting cable with one or two more
conductors than the immediate application requires.
. Check the ratings on the product to make sure the
product is suitable for your application.
. Installer must be a trained, experienced service tech-
. Allow thermostat to warm to room temperature before
. After installation is complete, check out product op-
The T8621 requires an additional conductor to
transformer common to provide continuous 24 V
power for thermostat operation.
eration as provided in these instructions.
Set the system switch in the OFF position before
mounting the subbase.
Disconnect power supply to prevent electrical shock
or equipment damage.
The subbase does not require leveling for proper opera-
tion, but for appearance only.
Remove thermostat from subbase (Fig. 1).
After wiring is complete, push excess wire back into
the hole, and plug hole with nonhardening caulk,
putty, or insulation to prevent drafts from affecting
The subbase mounts directly onto the wall with the
screws and anchors included in the package. If drywall
construction, plastic anchors must be used; use the sub-
base as a template, and with a pencil, mark the two
mounting screw positions (Fig. 2). Use 3/16 in. bit to drill
holes for anchors. Gently tap anchors into holes until they
are flush to the wall surface. Thread wires through the
center opening of the subbase. Then, mount the subbase
using two screws provided. Gently tighten screws, level top
surface of subbase, then securely tighten screws.
Install thermostat and subbase about 5 ft. [1.5 m] above
the floor in an area with good air circulation at room
Do not install the thermostat where it may be affected
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 behind the thermostat,
such as an outside wall.
IF REPLACING AN EXISTING THERMOSTAT
Turn power to thermostat off at furnace or boiler. A two
transformer system may require turning off two switches or
disconnects. Remove any existing wallplate or subbase
from wall. Label or write down each wire color with the letter
or number on the wiring terminal as the wire is removed, to
avoid miswiring later.
HEAT AUTO COOL OFF
Fig. 1—Removing thermostat from subbase.
Form Number 69-0330—3
©Honeywell Inc. 1990