Honeywell VVT User manual

J. H. • 7-92 • © Honeywell Inc. 1992 • Form Number 69-0726
VVT, VVT-HC (T641A,C)
Floating Control Thermostats
Installation Instructions for the Trained Service Technician.
Application
TheVVTandVVT-HCThermostatsprovidespdtoutputs
to control floating actuators in applications such as variable
air volume (VAV) terminal units.
—VVT (T641A): standard spdt floating control
thermostat.
—VVT-HC (T641C): provides manual heat/cool
changeover switch.
Operation
FLOATING CONTROL
The control provided by the thermostat is conventionally
calledfloatingcontrol.Duringfloatingcontrol, avariationof
two-position control, the thermostat provides a three output
control, which is Advance motor, Reverse motor, and Hold.
On a change in temperature, the thermostat drives the
actuatorto an intermediateposition and thenopens the circuit
to the actuator. The actuator remains in this position until
there is a temperature change at the thermostat. The actuator
is said to float between the limits of the thermostat to satisfy
various load requirements.
VAV SYSTEMS
VAV systems control the temperature within a space by
varying the volume of supply air. Air is delivered to the space
at a fixed temperature. The volume of supply air is controlled
by the space thermostat modulating the supply air damper.
Whenfullheatingandcoolingflexibilityisrequiredinazone,
it is handled by perimeter heating, or reheat capability in the
air terminal units. As individual zones shut down, the total air
flowinthesystemisregulatedbyacentralductstaticpressure
controller. The fan system is sized to handle an average peak
load, not the sum of the individual peaks. Because each zone
peaksat a different time ofday, extraair is borrowed from the
off-peak zones. This transfer from low-load to high-load
zones occurs only in true VAV systems.
Pressure dependent systems do not incorporate an indi-
vidual zone air flow sensor and depend on a stable system
pressure to maintain flow. These systems require slower
motorssuchasthesevenminutedampers,whicharetypically
controlled by the VVT (T641A) or VVT-HC (T641C) Ther-
mostats.
HEAT ANTICIPATION/COOL ANTICIPATION
Control of heating or cooling units with a thermostat does
notallow forthe temperatureto remainexactly atthe thermo-
stat set point, but varies within a certain temperature range.
Anticipation is added to the thermostat to reduce
this range.
The anticipator is a small resistive heater in the thermostat
that heats when the system is on or off. The heat produced by
theanticipatorraisestheinternalbimetaltemperatureslightly
faster than the surrounding room temperature. The thermo-
stat anticipates the need to shut off the heating system sooner
thanit would if affected byroom temperature only. The VVT
(T641A) or VVT-HC (T641C) have fixed or voltage antici-
pation.
Installation
WHEN INSTALLING THIS PRODUCT…
1. Read these instructions carefully. Failure to follow
them could cause a hazardous condition.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for your
application.
3. Installer must be a trained experienced service
technician.
4. After installation is complete, check out product op-
eration as provided in these instructions.
CAUTION
1. Disconnect power supply to prevent electrical
shock or equipment damage.
2. Topreventinterferencewiththethermostatlink-
age, keep wire length to a minimum and run
wires as close as possible to the subbase.
3. Donotovertightenthermostatcaptive 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:Anincorrectlyleveledthermostatwill cause
the temperature control to deviate from set point. It is
not a calibration problem.
!

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
backinto the wall later. Thread wires throughhole inpacking
materialsaved in step1. Connectthewires tothe 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:Anincorrectlyleveledthermostatwillcause
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
ensureproper thermostat calibration and operation,
the Cterminal 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
1L1
(HOT) L2
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
!
Fig. 1—Functional equivalent anticipator circuit of thermostat.

3 69-0726
Fig. 2—Thermostat components and leveling procedure.
80
70
60
50
;;;;;
SPIRIT LEVEL WALLPLATE
HEATING
CONTACT
MOUNTING
HOLES (4)
COOLING
CONTACT
INTERNAL
SET POINT
LEVER
FRONT OF THERMOSTAT
(COVER REMOVED)
YC
X
W
R
MOUNTING
HOLES (4)
BACK OF VVT(T641A)
4C
X
6
5
MOUNTING
HOLES (4)
BACK OF VVT-HC (T641C)
Fig. 3—Mounting thermostat using accessory wallplate.
80
70
60
50
WARM
COOL
HONEYWELL PART NO. 221618
ACCESSORY WALLPLATE
THERMOSTAT BASE
MOUNTING
SCREWS (4)
THERMOSTAT COVER
M6111
EXTERNAL
SET POINT LEVER
M6110

M6113
1L1
(HOT)
L2
5R
C4
W6Y
1 234
567
8
1L1
(HOT)
L2
5R
C4
W6Y
CW
(OPEN)
COM
CCW
(CLOSED)
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
VVO BD
DAMPER CDO-52
VVA RD
DAMPER
VVT (T641A)
OR
VVT-HC (T641C)
Settings
TEMPERATURE SETTING
Move the heating and cooling set point levers to the
desired comfort positions. See Fig. 3.
SWITCH SETTING
TheVVT-HT(T641C)hasamanualheat/coolchangeover
switch. With this switch set in the cool position, wire to
damper actuator as shown in Fig. 4. Be sure to determine
direction of damper opening for correct wiring between the
thermostat and the actuator. The changeover switch can be
placedin the heatposition to reverseaction at terminals4 (W)
and 6 (Y).
Checkout
WiththeVVT(T641A)orVVT-HC(T641C) Thermostat
controlling the damper or equivalent actuator, lower the set
point of the thermostat to call for cooling. Observe the
operationofthemotor.Ifthedamper is closed, itshouldbegin
to open. If not, adjust the set point of the thermostat higher to
determine if the wiring is correct. If no movement is ob-
served, check for the presence of 24 Vac between terminals
of the motor during a call for cooling. With the proper wiring
and 24 Vac present, the actuator should operate correctly. If
24 Vac is not present on a call for cooling, replace the
thermostat.
To check out the damper when controlled by the thermo-
stat, determine the direction the damper shaft moves to open
thedamper.Place24Vacacrosstheappropriatecommonand
openterminal to energize the actuatorafter disconnectingthe
external wires. The damper should begin to open the damper.
If the motor does not run, try switching the 24 Vac across the
opposite terminals to determine if the damper will begin to
close. Replace the damper if the motor does not run in either
direction.
Fig. 4—Dampers used with VVT (T641A) and VVT-HC (T641C) Thermostats for Type B damper applications.
Y terminal energizes counterclockwise (ccw) winding on call for cooling, driving motor open.
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