2
CAUTION
1. Disconnect power supply to prevent electrical
shock or equipment damage.
2. To prevent interference with the thermostat link-
age, keep wire length to a minimum and run
wires as close as possible to the subbase.
3. Do not overtighten thermostat captive mounting
screws, because damage to subbase threads can
result.
4. Do not short across coil terminals on relay. This
can burn out the thermostat heat anticipator.
IMPORTANT: An incorrectly leveled thermostat will cause
the temperature control to deviate from set point. It is
not a calibration problem.
LOCATION
Install the thermostat about 5 ft. [1.5 m] above the floor in
an area with good air circulation at average temperature.
Do not install the thermostat where it may be affected
by—
— drafts, or dead spots behind doors and in corners.
— 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.
MOUNTING AND WIRING
IMPORTANT: The T641 is electrically compatible and
designed to operate with actuators that have seven
minute timings for a full stroke of 90
°
(angular). Using
with motors that have timings less than seven minutes
(90
°
full stroke) will result in unstable temperature
control.
The thermostat can be mounted on a horizontal outlet box
or directly on the wall. Choose the method that best fits your
installation.
In replacement applications, check the existing thermo-
stat wires for cracked or frayed insulation. Replace any
wires in poor condition. All wiring must comply with local
codes and ordinances. The T641 utilizes a four-wire opera-
tion, so an additional transformer common wire must be
present for correct wiring and operation. See Fig. 2 for
functional schematic of T641. Screw terminals are on the
back of the thermostat. See Fig. 3.
The part no. 221618 Cover Plate is available when replac-
ing a competitive device that has left marks on the wall. See
Fig. 4.
1. Grasp the thermostat cover at the top and bottom with
one hand. Pull outward on bottom edge of the cover until it
snaps free of the thermostat base. Carefully remove and save
the packing material surrounding the mercury switches. See
Fig. 3.
2. Run wiring from the actuator (if necessary) to the
location. If the wiring is plastered into the wall, make a hole
next to the cable and loosen the wires so they can be pushed
back into the wall later. Thread wires through hole in packing
material saved in step 1. Connect the wires to the terminals on
the back of the thermostat. See Figs. 5 and 6.
3. Push the excess wire back through the hole and plug
any opening with packing material to prevent drafts that may
affect thermostat performance.
4. Through the thermostat two middle mounting holes,
use the screws provided to loosely secure the T641 to the wall
or outlet box.
5. Level the thermostat exactly using a spirit level or
plumb line. Tighten the two mounting screws at the middle
of the device. See Fig. 3.
Fig. 2—Functional equivalent anticipator circuit of T641.
HEAT
FALL
HEAT
ANTICIPATOR
COOL
ANTICIPATOR
COOL
RISE
SOLID STATE RELAY
SOLID STATE RELAY
N.C.
N.O.
R
Y
C
W
DAMPER CONTROL
DRIVE
CLOSED
COIL
DRIVE
OPEN
COIL
M6112
1
L1
(HOT) L2
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
X
SYSTEM OVERIDE RELAY
ON
SYSTEM
OVERIDE
2
2
OFF
ONLY T641B HAS SYSTEM OVERRIDE SWITCH.