Honeywell T921F Thermostat User Manual

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T921A,B,E-G Proportional

Control Thermostats

T921 Thermostats provide 3-wire, low voltage

proportionalcontrolforSeries90(135ohm)valve

motors, damper motors, and balancing relays in

heating or cooling system applications.

■

T921A

■ T921B

■ T921E

■ T921F

■ T921G

Accessoryfaceplatesavailableforhorizontalmount-

ing of T921A,B,E models.

■ A bellows element adjusts the potentiometer slider

to regulate motor operation.

■

COOL-HEAT changeover switch in the T921B.

Night setback mechanism and switch in the T921E.

■ Various temperature ranges are available.

■ All models are available with a thermometer and a

locking cover.

A spdt (single pole double throw) Class 2 auxiliary

switch in the T921F,G, which operates at the low

(T921F) and high (T921G) end of the throttling

range.

CONTENTS

Specifications ................................................. 2

Ordering Information ..................................... 2

Installation ..................................................... 4

Setting and Adjusting ..................................... 7

Operation ....................................................... 7

J. D. • Rev. 1 1- 94 • ©Honeywell Inc. 1994 • Form Number 66 00 -- 22 22 44 22 —— 22

T921A,B,E-G

SPECIFICATIONS • ORDERING INFORMATION

Specifications

THERMOMETER: Bimetal. Scale ranges T921A only:

45°to 75° F [7° to 24° C]. All other models: 60° to 90° F

[16° to 32° C], 15°to 35° C [59° to 95°F]. T921A is also

available with a blank cover and no thermometer.

AUXILIARY SWITCH DIFFERENTIAL:

T921F: 2° F [1° C].

TRADELINE MODELS

TRADELINE models are selected and packaged to

provide ease of stocking, ease of handling and maximum

replacement value. TRADELINE model specifications

are the same as those of the standard models except as noted

below.

TRADELINE MODEL AVAILABLE:

T921G: 1° F [0.5° C].

T921A Thermostat for vertical or horizontal mounting.

TEMPERATURE RANGE AND SCALE:

THROTTLING RANGE:

Fixed.

56° to 84° F [13° to 29°].

T921A: 2.5° F [1° C] midscale.

ADDITIONAL FEATURES:

T921B,E: 4° F [2° C].

T921F: 6° F [3° C].

T921G: 5° F [2.5° C].

•

TRADELINE packed with cross-reference label

and special TRADELINE instructions.

•

T6051A may be used in electric heat systems.

They all include slotted sides and an add-on faceplate

to allow the thermostat to be mounted horizontally.

They also include the 127246A Adapter Plate As-

sembly for vertical mounting on a horizontal conduit

box or for horizontal mounting on a vertical conduit

box.

Variable.

T921A model available with potentiometer for 5° to

6° F [2.5 to 3° C] throttling range.

ELECTRICAL RATINGS:

Voltage: 24 to 30 Vac.

Auxiliary Switch Contact Rating (When Used For Pilot

Duty): 100 VA at 30 Vac.

DIMENSIONS:

STANDARD MODEL

Refer to Fig. 1.

MODELS:

ACCESSORIES (ORDER SEPARATELY):

127246A Adapter Plate Assembly for mounting all mod-

els vertically on a horizontal conduit box. (T921

modelsareshippedwithafaceplateforverticalmount-

ing.)

T921A: Heating or cooling applications.

T921B: Is the same as the T921A but includes a cool-

heat changeover switch.

T921E: Includes a switch and heater that provide a night

setback of approximately 10° F [5.5° C].

T921F: Includes an spdt low voltage Class 2 auxiliary

switch that operates at the low end of the throttling

range.

When mounting the T921A,B,E horizontally, see

Table 1 to order the faceplate with the appropriate

scale. NOTE: Do not mount the T921F,G horizon-

tally.

T921G: Includes an spdt low voltage Class 2 auxiliary

switch that operates at the high end of the throttling

range.

34297B Thermostat Guard Assembly and 138541A

Mounting Plate.

133722A Thermostat Guard (clear plastic cover).

133723A Thermostat Guard (beige plastic cover).

SETTING ADJUSTMENT RANGE:

T921A,B,E-G: 56° to 84° F [13° to 29° C].

T921A,B,E-G: 13° to 29° C [56° to 84° F].

T921A: 42° to 75° F [ 5° to 24° C].

T921A,B: 66° to 95° F [19° to 35° C].

Ordering Information

When purchasing replacement and modernization products from your TRADELINE wholesaler or your distributor, refer to the

TRADELINE Catalog or price sheets for complete ordering number or specify—

. Model number.

. Scale range.

. Accessories, if desired.

If you have additional questions, need further information, or want to comment on our products or services, please write or phone:

. You local Honeywell Home and Building Control Sales Office (check the white pages of the phone directory).

. Home And Building Control Customer Satisfaction

Honeywell Inc., 1885 Douglas Drive North

Minneapolis, Minnesota 55422 1-800-468-1502

(In Canada—Honeywell Limited/Honeywell Limitee, 740 Ellesmere Road, Scarborough, Ontario M1P 2V9) International Sales

and Service Offices in all Principal Cities of the world. Manufacturing in Australia, Canada, Finland, France, Germany, Japan,

Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A.

0-2242—2

T921A,B,E-G

SPECIFICATIONS

640HX Averaging Element Mounting Kit: For mount-

ing in existing installations where access to the duct

is impractical.

Fig. 1—T921 approximate installation dimen-

sions in in. [mm].

ACCESSORY ADAPTER PLATE (127246A) FOR

MOUNTING ON HORIZONTAL CONDUIT BOX

SETTING

ADJUSTMENT

KNOB

Q615A Enclosure: To protect the device when mounted

outside; splash proof.

801534 Calibration Wrench.

HORIZONTAL CONDUIT BOX

FOR VERTICAL

CONDUIT BOX (2)

07324A Bulb Holder: For mounting the bulb in a duct.

4886A Outdoor Bulb Shield: To protect the outdoor

bulb mounting.

Fig. 2—T991B approximate installation

dimensions in in. [mm].

[

[137]

[194]

84]

145]

[

24]

KNOCKOUT FOR 1/2 INCH

CONDUIT (BOTH ENDS)

[78]

[108]

[57]

[84]

2 [51]

[57]

[10]

[86]

[57]

2-11/16 [69] INCHES FOR

T921F, G MODELS.

M9107

[135]

[

45]

TABLE 1—ACCESSORY FACEPLATE.

106]

[

Scale

Part No.

135135A

135135B

135135C

135135D

135135C^a

6° to 84° F [13° to 29° C]

3° to 29° C [56° to 84° F]

2° to 75° F [5° to 24° C]

6° to 95° F [19° to 35° C]

6° to 84° F [13° to 29° C]

[

143]

[6]

DIAMETER (3)

^aBlank faceplate.

[24]

[10]

32]

DIAMETER

[

REPLACEMENT PART:

130224 Locking Cover Knob.

OPTIONAL SPECIFICATION (USING THE T991B):

Alternate proportional control similar to the T921A, but

uses an outdoor temperature, automatic control point

reset.

T991B with 3-1/2: 1 reset and 50° to 120° F [10° to

OUTDOOR BULB SIZE VARIES INVERSELY WITH THE RESET RATIO.

9° C] temperature setting scale (when the outdoor

bulb is at 60° F [16° C]).

DIMENSIONS:

INDOOR BULB LENGTH AND DIAMETER IS 4-1/2 [114] INCH BY

/2 [13] INCH EXCEPT FOR THE AVERAGING ELEMENT WHICH IS

/8 [3] INCH DIAMETER BY 12 FT. [3 M] LONG.

Refer to Fig. 2.

CLEARANCE NECESSARY TO REMOVE COVER.

M9108

ACCESSORIES:

Compression fittings, immersion wells: Refer to the

appropriate specification or the TRADELINE Cata-

log.

14439 Mounting Clips: For mounting a capillary tub-

ing (averaging element) in a duct.

60-2242—2

T921A,B,E-G

INSTALLATION

Installation

ADD FACEPLATES FOR HORIZONTAL

MOUNTING (T921A,B,E ONLY)

CAUTION

T921 models are shipped with a faceplate for vertical

mounting. When mounting the T921A,B,E horizontally,

see Table 2 to order the faceplate with the appropriate scale.

NOTE: Do not mount the T921F,G horizontally.

Disconnect power supply before installation to

prevent electrical shock and equipment damage.

WHEN INSTALLING THIS PRODUCT…

. Installer must be a trained, experienced service tech-

nician.

TABLE 2—ACCESSORY FACEPLATE

Scale

Part No.

135135A

135135B

135135C

135135D

135135C^a

2. All wiring must comply with applicable electrical

6° to 84° F [13° to 29° C]

3° to 29° C [56° to 84° F]

2° to 75° F [5° to 24° C]

6° to 95° F [19° to 35° C]

6° to 84° F [13° to 29° C]

codes, ordinances and regulations.

3. Do not exceed the ratings listed on the device name-

plate.

4. After the installation is complete, conduct a thorough

checkout of the product operation.

LOCATION

^aBlank faceplate.

Locate the thermostat about 5 feet [1.5m] above the

floor in an area with good air circulation at average room

temperature.

Affix the accessory faceplate when mounting the

T921A,B,E models horizontally with contemporary cov-

ers. Peel the backing strip from the faceplate and place it

lightly over the vertical faceplate. Align the edges and

corners and make sure the scales align with the markings.

Press firmly over the entire surface. Do not attempt to

reapply once the faceplate has been mounted.

Do not mount the thermostat where it can be affected by:

—

drafts, or dead spots behind doors and in corners.

hot or cold air from ducts.

radiant heat from the sun or appliances.

concealed pipes and chimneys.

unheated (uncooled) areas such as an outside wall

behind the thermostat.

MOUNTING

Fig. 3—Vertical mounting of T921A,B,E-G

Thermostats on vertical conduit box.

T921A,B,E Thermostats can also be mounted

horizontally on horizontal conduit box using

add-on faceplate. (Do not mount T921F,G

horizontally.)

1. Disconnect power supply before installation to pre-

vent electrical shock and equipment damage.

2. Loosen the locking screw at the bottom of the case

with an Allen wrench.

3. Lift off the thermostat cover.

. Remove the mounting screws that secure the thermo-

NOTE: ACCESSORY FACEPLATE FOR USE WHEN

THE THERMOSTAT IS MOUNTED HORIZONTALLY.

PEEL OFF BACKING AND APPLY OVER VERTICAL

FACEPLATE AFTER MOUNTING IS COMPLETE.

stat to the backplate and remove the backplate.

. Fasten the backplate to the conduit box (see Fig. 3).

Use the 127246A Adapter Plate Assembly (ordered sepa-

rately) to mount the thermostat vertically on the horizontal

conduit box; or to mount the thermostat horizontally on the

vertical conduit box (see Fig. 4).

CONDUIT

BOX

MOUNTING

SCREWS

NOTE: When an accessory adapter plate is used, fasten the

adapter plate to the conduit box with the two screws

provided. Then fasten the backplate to the adapter plate.

BACKPLATE

6. Make all electrical connections to the terminals on

60 70 80 90

LOCKING

SCREW

the back of the thermostat before mounting the instrument

on the backplate. Refer to the Wiring section.

H O N E Y W E L L

COVER

M9037

7. Mountthethermostatonthebackplatewiththemount-

ing screws.

8. After performing the checkout tests, replace the ther-

mostat cover and tighten the locking screw.

0-2242—2

T921A,B,E-G

INSTALLATION

Fig. 4—Vertical mounting of T921A,B,E-G

Thermostats on horizontal conduit box.

T921A,B,E Thermostats can also be mounted

horizontally on vertical conduit box using

add-on faceplate. (Do not mount T921F,G

horizontally.)

Fig. 5—Terminals on back of thermostats.

TOP

NOTE: ACCESSORY FACEPLATE FOR USE WHEN THE THERMOSTAT

IS MOUNTED HORIZONTALLY. PEEL OFF BACKING AND APPLY

OVER VERTICAL FACEPLATE AFTER MOUNTING IS COMPLETE.

CONDUIT

BOX

BACKPLATE

MOUNTING

SCREWS

(BLACK)

T921A, B

T921E

H (HEATER)

27246A

TOP

70 80 90

ACCESSORY

ADAPTER

PLATE

LOCKING

SCREW

E Y W E L L

COVER

M9036

WIRING

Be sure all wiring must complies with applicable electri-

cal codes, ordinances and regulations.

Do not exceed the following electrical ratings:

Voltage: 24 to 30 Vac.

Auxiliary Switch Contact Ratings: 100 VA at 30

Vac.

Make all electrical connections to the terminals on the

back of the thermostat before mounting the instrument onto

the conduit box. Terminal locations for all models are

shown in Fig. 5. Note the difference in terminal designa-

tions for the auxiliary switch on the T921F and G. The H

Heater) terminal on the T921E is a black leadwire.

Typical wiring diagrams are shown in Figs. 6 through

0. Wire the T921 color-to-color when the modulating

motor must drive the valve or damper open on temperature

fall (heating application). When opposite motor action is

required, reverse the B and W connections. Refer to the

appropriate instructions when wiring the 2-position actua-

tor (Figs. 9 and 10).

AUXILIARY

SWITCH

TERMINALS

T921F

T921G

M9038

Fig. 6—Typical wiring diagram for T921A.

(

SERIES 90

MODULATING

MOTOR

T921A

(

HOT)

TRANSFORMER

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

INTERCHANGE B AND W CONNECTIONS TO REVERSE

DIRECTION OF MOTOR TRAVEL.

M5989

60-2242—2

T921A,B,E-G

INSTALLATION • SETTING AND ADJUSTING

Fig. 7—Typical wiring diagram for T921B.

Fig. 9—Typical wiring diagram for T921F.

SERIES 90

MODULATING

MOTOR

T921F

SERIES 90

MODULATING

MOTOR

T921B

(

HOT)

TRANSFORMER

(HOT)

TRANSFORMER

-POSITION

ACTUATOR

AUXILIARY

SWITCH

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

INTERCHANGE B AND W CONNECTIONS TO REVERSE

DIRECTION OF MOTOR TRAVEL.

M5992

CLASS 2 POWER SUPPLY.

INTERCHANGE B AND W CONNECTIONS TO REVERSE

DIRECTION OF MOTOR TRAVEL.

USE FOR CLASS 2 CIRCUITS. MAKES R TO B ON

TEMPERATURE FALL BELOW THROTTLING RANGE:

2˚ F [1˚ C] DIFFERENTIAL. SEE FIG. 10.

M5993

Fig. 8—Typical wiring diagram for T921E.

Fig. 10—Typical wiring diagram for T921G.

SERIES 90

MODULATING

MOTOR

T921G

TIMER SWITCH

(OPTIONAL)

T921E

HEATER

NIGHT

SETBACK

SWITCH

(HOT)

TRANSFORMER

(HOT)

2-POSITION

ACTUATOR

TRANSFORMER

SERIES 90

MODULATING

MOTOR

AUXILIARY

SWITCH

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

CLASS 2 POWER SUPPLY.

H TERMINAL IS A BLACK LEADWIRE.

M5988A

INTERCHANGE B AND W CONNECTIONS TO REVERSE

DIRECTION OF MOTOR TRAVEL.

USE FOR CLASS 2 CIRCUITS. MAKES R TO B ON

TEMPERATURE RISE ABOVE THROTTLING RANGE:

1˚ F [0.5˚ C] DIFFERENTIAL. SEE FIG. 11.

M5996

Setting and Adjusting

ADDITIONAL FEATURES:

TEMPERATURE SETTING

Adjust all T921 models at the top of the thermostat for

vertically mounted models and on the left side for horizon-

tally mounted models using the setting adjustment knob or

an Allen wrench (see Fig. 11). The device is shipped with

the temperature setting indicator at the center of the tem-

perature range. Without removing the cover, turn the set-

ting adjustment knob or use an Allen wrench so the indica-

tor is at the desired average room temperature.

T921B SUMMER-WINTER CHANGEOVER

TheT921Bincludesasummer-winterchangeoverswitch.

It is labeled COOL-HEAT. For horizontally mounted

models, this switch is located on the left side of the

thermostat. For vertically mounted models, it is lo-

cated on the top of the thermostat (see Fig. 11).

T921E NIGHT SETBACK

The T921E includes a manual night setback switch

located on the top of the thermostat (see Fig. 11).

0-2242—2

T921A,B,E-G

SETTING AND ADJUSTING • OPERATION

This switch energizes a heater that offsets the ther-

mostat approximately 10° F [6° C], lowering the

temperature for night operation. Leave this switch in

the OFF position for normal operation; turn it to the

ON position for lower night time temperature.

Fig. 11—Internal view of vertically mounted

T921 (horizontally mounted model is similar).

POTENTIOMETER

WIPER

SETTING

ADJUSTMENT KNOB

CALIBRATION

IMPORTANT: Do not recalibrate unless the thermostat

continues to be out-of-adjustment after several hours

of operation.

TEMPERATURE

SETTING

INDICATOR

LOCK SCREW

T921 Thermostats are calibrated at the factory so when

the room temperature matches the setpoint temperature, the

wiper is at the center of the active potentiometer winding.

If the thermostat is out of calibration, proceed as follows

(

see Fig. 11):

1. Remove the thermostat cover.

. Turn the thermostat setting adjustment knob or an

BELLOWS

Allen wrench until the valve or damper motor is at mid-

point.

. Loosen the indicator lock screw and move the indica-

tor to room temperature. Tighten the lock screw.

. Replace the thermostat cover. Recheck the calibra-

SUMMER-WINTER (COOL-HEAT) CHANGEOVER SWITCH ON

T921B ONLY; NIGHT SETBACK SWITCH ON T921E ONLY. M9039

tion and repeat the procedure if necessary.

Operation

In the T921, a vapor-filled bellows moves the potenti-

ometer wiper by expanding or contracting in proportion to

temperature changes. As the wiper moves, the appropriate

motor winding is energized, opening or closing the valve or

damper to compensate for the temperature change in the

controlled area.

Fig. 12—T921F auxiliary switch operation.

TEMPERATURE

3˚ F

[+1.5˚ C]

THROTTING

RANGE (6˚ F [4˚ C])

Operation of the auxiliary switch in the T921F,G is

shown in Figs. 12 and 13.

See Table 3 for the throttling range of each thermostat.

The T921F Auxiliary Switch makes R-W at the low end of

the throttling range on temperature rise and makes R-B at

SETPOINT

TEMPER-

ATURE

° F [1° C] below the low end of the throttling range on

temperature fall.

The T921G Auxiliary Switch makes R-W at the high

end of the throttling range on temperature fall and R-B at

TEMPERATURE

FALL

3˚ F

R-W MAKES

[

-1.5˚ C]

° F [0.5° C] above the high end of the throttling range on

˚ F [1˚ C]

temperature rise.

TEMPERATURE

RISE

DIFFERENTIAL

R-B MAKES

M5990

TABLE 3—THERMOSTAT THROTTLING RANGES

Model

T921A

T921B

T921E

T921F

T921G

Throttling Range

2.5° F [1.5° C] midscale

4° F [2° C]

6° F [4° C]

5° F [3° C]

60-2242—2

T921A,B,E-G

OPERATION␣

T921B

Fig. 13—T921G auxiliary switch operation.

1. Place the changeover switch (see Fig. 11) in the

HEAT position and follow steps 1 through 3 of the T921A

procedure.

2. Move the switch to the COOL position and repeat

steps 1 through 3 of the T921A procedure.

3. If the valve or damper responds properly to the

thermostat, move the setpoint to the desired temperature.

TEMPERATURE

FALL

R-B MAKES

[

2.5˚ F

1˚ F [0.5˚ C]

DIFFERENTIAL

+1.5˚ C]

R-W MAKES

TEMPERATURE

RISE

T921E

SETPOINT

TEMPER-

ATURE

1. Place the night setback switch (see Fig. 11) in the

OFF position and follow steps 1 through 3 of the T921A

procedure.

THROTTING

RANGE (5˚ F [3˚ C])

. Move the setpoint 5° F [3° C] above room tempera-

ture; the valve or damper should open.

. Move the night setback switch to the ON position; as

-2.5˚ F

[

-1.5˚ C]

the heater in the thermostat warms up, the valve or damper

should be driven toward the closed position. Allow 30

minutes for the heater and bellows to warm up.

M5991

. If the valve or damper responds properly to the

CHECKOUT

thermostat, move the setpoint to the desired temperature.

After the thermostat is wired and mounted, check to be

sure the thermostat and controlled equipment are function-

ing properly. Before proceeding, allow from one to three

hours for the system to stabilize.

T921F

1. Follow steps 1 through 3 of the T921A procedure.

2. Move the setpoint at least 10° F [6° C] above room

temperature. The auxiliary switch should be make R-B and

the valve or damper should be open (for heating applica-

tion). Lower the setpoint gradually; the auxiliary switch

should make R-W before the setting indicator reaches room

temperature. As the setting indicator moves below room

temperature, the valve or damper should be driven closed.

3. If the valve or damper responds properly to the

thermostat, move the setpoint to the desired temperature.

T921A

1. Set the temperature setting indicator to room tem-

perature by using the setting adjustment knob, or an Allen

wrench (see Fig. 11). The valve or damper motor should be

at midpoint.

2. Move the setpoint 5° F [3° C] below room tempera-

ture. In a heating application, the valve or damper should

close; in a cooling application, the valve or damper should

open. If the valve or damper is driven in the opposite

direction, interchange the wires at the B and W terminals.

T921G

1. Follow steps 1 through 3 of the T921A procedure.

. Move the setpoint at least 6° F [4° C] below room

NOTE: If a proportional action limit control is used, the

motor may not move the damper or valve all the way

closed or open. Check the limit action after interchang-

ing the wiring.

temperature. The auxiliary switch should be made R-B and

the valve or damper should be closed (for heating applica-

tion). Raise the setpoint gradually; the auxiliary switch

should make R-W before the setting indicator reaches room

temperature. As the setting indicator moves above room

temperature, the valve or damper should open.

3. Move the setpoint 5° F [3° C] above room tempera-

ture. In a heating application, the valve or damper should

open; in a cooling application, the valve or damper should

close.

4. If the valve or damper responds properly to the

thermostat, move the setpoint to the desired temperature.

4. If the valve or damper responds properly to the

thermostat, move the setpoint to the desired temperature.

Home and Building Control

Helping You Control Your World

Honeywell Inc.

Honeywell Limited—Honeywell Limitée

740 Ellesmere Road

985 Douglas Drive North

Golden Valley, MN 55422

Scarborough, Ontario

M1P 2V9

QUALITY IS KEY

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