2
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 VVT (T641A) and VVT-HC (T641C)
are 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 thermostat utilizes a four-wire opera-
tion, so an additional transformer common wire must be
present for correct wiring and operation. See Fig. 1 for
functional schematic of thermostat. Screw terminals are
located on the back of the thermostat. See Fig. 2.
The Honeywell part no. 221618 Cover Plate is available
when replacing a competitive device that has left marks on
the wall. See Fig. 3.
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 Fig. 4.
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 thermostat to
the wall or outlet box.
5. Level the thermostat exactly using a spirit level or
plumb line. Tighten the two mounting screws in the middle
of the device. See Fig. 3.
IMPORTANT: An incorrectly leveled thermostat will cause
the temperature control to deviate from set point. It is
not a calibration problem.
6. Install two screws in top mounting holes and tighten.
7. Replace the thermostat cover.
WARNING
Because the cooling anticipator operates con-
tinuously in the floating band, the VVT (T641A)
and VVT-HC (T641C) Thermostats incorporate a
factory offset that calibrates the thermostat. The
offset causes the thermostat to appear to be switch-
ing 10.5
°
F lower when not powered compared to
actual operation. The cooling anticipator is needed
to provide proper thermostat cycling by matching
the current draw of the damper actuator. To
ensure proper thermostat calibration and operation,
the C terminal must be used.
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.
!
Fig. 1—Functional equivalent anticipator circuit of thermostat.