Honeywell T8621A User Manual

Chronotherm™ III Fuel

Saver Thermostats

The T8621A,C,D Chronotherm III Program­mable Fuel Saver Thermostats provide auto­matic control of single or multistage heating/
cooling systems and offer users the highest
standard of comfort and convenience available
with energy savings.

T8621A,C,D

■ Full seven-day program capability; different sched-

ules may be selected for every day.

■ Can be programmed in hand (with batteries in-

stalled) or on wall to provide up to four temperature

settings per day.

■ Large digital clock (liquid crystal display) indi-

cates continuous time, day, current period and

room temperature.

■ Adaptive Intelligent Recovery™ brings room

temperature to programmed temperature at pro-

grammed time, maximizing comfort and energy

savings.

■ Temperature control program maintains tempera-

ture within 1° F of setpoint.

■ Temporary program override available by using—

—WARMER and COOLER keys

—SKIP next period key

—CHANGE to last period key

■ HOLD TEMP key provided for indefinite pro-

gram override (vacation/holiday).

■ Installer self-test and time delay override save

installation time.

■ SYSTEM light-emitting diode (LED) indicates

system is energized.

■ Models available with automatic or manual heat/

cool changeover.

■ Batteries included provide power to maintain

clock and memory during power failures.

■ Switching subbase with wiring terminals included.

■ Powered directly from control transformer, requir-

ing an extra (24V) wire to thermostat.

■ Fan operation switch included on back of SUPER

TRADELINE models to select either indepen­dent or direct thermostat control of fan in heating.

■ Models available with separate sensor for remote

mounting.

CONTENTS

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

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

Selection/Application ................................... 5

Installation ................................................... 7

Checkout..................................................... 17

Programming the Thermostat ....................19

Operating the Thermostat ..........................25

Operation ................................................... 28

Troubleshooting ......................................... 29

Glossary ..................................................... 30

Table of Contents ....................................... 31

C. H. • Rev. 8-92 • ©Honeywell Inc. 1992 • Form Number 68-0058—1

1 68-0058—1

T8621A,C,D
SPECIFICATIONS • ORDERING INFORMATION

Specifications

IMPORTANT: The specifications given in this publica-

tion do not include normal manufacturing toler­ances. Therefore, this unit may not exactly match
the listed specifications. Also, this product is
tested under closely controlled conditions, and
some minor differences in performance can be
expected if those conditions are changed.

SUPER TRADELINE FEATURE: Fan operation switch

on back of thermostat to select either independent or
direct thermostat control of fan in heating.

TRADELINE MODELS

TRADELINE models, see Table 2, are selected and pack-

aged to provide ease of stocking and handling and also
maximum replacement value.

SUPER TRADELINE MODEL

SUPER TRADELINE controls, see Table 1, offer fea-

tures not available on TRADELINE models and are

designed to replace a wide range of Honeywell and

competitive controls.

TABLE 1—SUPER TRADELINE MODEL.

Thermostat

Model Stages Changeover Switching

Number Heat Cool Type System Fan Application

T8621D 2 2 Manual HEAT-OFF-COOL ON-AUTO Multistage

LIGHT-EMITTING DIODE (LED): SYSTEM LED

lights during thermostat ON cycle.

VOLTAGE RATING: 15 to 30 Vac.

Ordering Information

When purchasing replacement and modernization products from your TRADELINE® wholesaler or distributor, refer to the
TRADELINE Catalog or price sheets for complete ordering number, or specify—

1. Model number; SUPER TRADELINE, if desired. 4. Remote temperature sensing, if desired.

2. Number of heat and cool stages desired. 5. Application.

3. System, fan switching desired.

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

1. Your local Honeywell Home and Building Control Sales Office (check white pages of your phone directory).

2. Home and Building Control Customer Satisfaction
Honeywell Inc., 1885 Douglas Drive North
Minneapolis, Minnesota 55422-4386 [phone]

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.

2

SPECIFICATIONS

TABLE 2—TRADELINE MODELS.

Thermostat

Model Stages Changeover Switching

Number Heat Cool Type System Fan Application

T8621A* 1 1 Auto HEAT-AUTO- ON-AUTO Single stage

COOL-OFF

T8621C 2 1 Auto HEAT-AUTO- ON-AUTO Multistage

COOL-OFF

T8621D* 2 2 Auto HEAT-AUTO- ON-AUTO Multistage

COOL-OFF

*Model available with separate sensor for remote mounting.

T8621A,C,D

CURRENT RATING: 1.6A maximum total per stage.
OPERATING HUMIDITY RANGE: 5 to 90 percent

relative humidity, noncondensing.

OPERATING AMBIENT TEMPERATURE RANGE:

40° F to 110° F [4° C to 43° C].

SETPOINT RANGE: 45° F to 88° F [7° C to 31° C].
CALIBRATION: Self-calibrating thermostat and ther-

mometer to ±1° F.

SHIPPING TEMPERATURE: -20° F to +120° F [-29° C to

+49° C].

CYCLES PER HOUR ADJUSTMENT:

Heating: First stage of 2-stage heat models—fixed at

3 cph. Second stage of 2-stage heat models or
heat stage of single-stage heat models—factory­set at

Fig. 1—T8621 Subbase mounting dimensions in in. [mm].

6 cph; adjustable for other systems.

Cooling: Factory-set at 3 cph (not field adjustable);

minimum off-time of five minutes.

FINISH: Beige matte with decorative brushed metal face-

plate.

DIMENSIONS: Thermostat (mounted on subbase)—7

in. [178 mm] long, 5-5/16 in. [135 mm] high, 1-3/
4 in. [44 mm] deep. See Fig. 1 for subbase dimen-

sions and Fig. 2 for sensor dimensions.
TYPICAL KEYPAD: See Fig. 3.
ACCESSORIES:

TG586A Locking Cover.

TG512 Versaguard Universal Thermostat Guard.
REPLACEMENT PARTS:

202905AA Remote Temperature Sensor Assembly.

Includes sensor, screws, anchors and instructions. See

Fig. 2 for dimensions.

31

1

32

[50]

5

5

16

[135]

M5181A

13

1

16

[46]

3

4 [121]

4

5

3 [83]

16

3

4

32

[104]

7 [179]

3 68-0058—1

T8621A,C,D
SPECIFICATIONS • SELECTION/APPLICATION

Fig. 2—202905AA Remote Temperature Sensor dimensions in in. [mm].

FRONT

3

4

32

[104]

SIDE

1

[50]

BACK

31
32

31

[50]

1

32

41

[16]

64

3

1

[35]

8

2

[51]

19

[8]

64

9

[4]

64

1

DIA.

2

[13]

[25]

1

M5244

Fig. 3—Typical thermostat keypad.

RUN

PROGRAM

SET
PRESENT
DAY/TIME

HOLD
TEMP

DAY

SET

HEAT/COOL

PERIOD

CANCEL

PERIOD

MIDDAY

COPY
FROM

WED

COPY

TO

AM

TIME

AHEAD

BACK COOLER

ROOM

HEAT ON

TEMPERATURE

PRESENT

SETTING

WARMER

FAN

SYSTEM

SKIP

NEXT

PERIOD

CHANGE
TO LAST

PERIOD

HEAT OFF

COOL

ON AUTO

M5360

4

T8621A,C,D
INSTALLATION

Fig. 9—T8621C 2-stage heat/1-stage cool thermostat with HEAT-AUTO-COOL-OFF system and AUTO-ON
fan switching.

HEATING
TRANSFORMER

4

POWER
SUPPLY

HIGH
LIMIT

HIGH
LIMIT

HEAT 1

R

2

3

C

HEAT RELAY 1

W1

1

L1
(HOT)

L2

THERMOSTAT
LOGIC CIRCUIT

SUBBASE
LOGIC/
CONTROL
CIRCUIT

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD

1

PROTECTION AS REQUIRED.
FOR SINGLE TRANSFORMER SYSTEM JUMPER R AND RC.

2

W2

Y1

G

2

RC

COOLING
TRANSFORMER

HEAT RELAY 2

COOLING
CONTACTOR

FAN RELAY

HEAT 2

SYSTEM
SWITCH

HEAT

AUTO
COOL

OFF

COOL

FAN
SWITCH

AUTO
ON

NOMINAL 24 Vac POWER MUST BE PRESENT BETWEEN R AND C FOR

3

THERMOSTAT OPERATION.

4

DENOTES THERMOSTAT TO SUBBASE INTERCONNECTION.

L1
(HOT)

L2

1

M5233

10