Honeywell T8624C User Manual

T8624C,D (5-1-1 Day

Programming) Chr onotherm

III Fuel Saver Thermostats

The T8624C,D Chronotherm III Program­mable Fuel Saver Thermostats provide auto­matic control of multistage heating/cooling sys­tems and offer users the highest standard of
comfort and convenience available with energy
savings.

■ Different schedules may be selected for week-

days, Saturday and Sunday.

■ Can be programmed in hand (with batteries in-

stalled) or on wall to provide up to four tempera-

ture settings per day.

■ Large digital clock (liquid crystal display) indi-

cates continuous time, day, current period and

room temperature.

■ Adaptive Intelligent Recovery™ brings room tem-

perature 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, re-

quiring an extra (24V) wire to thermostat.

■ Fan operation switch to select either independent

or direct thermostat control of fan in heating
included on back of select models.

CONTENTS

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

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

Selection/Application .....................................4

Installation .....................................................5

Checkout.......................................................11

Programming the Thermostat ......................14

Operating the Thermostat ............................18

Troubleshooting ...........................................21

Glossary .......................................................22

®

C.H. • 9-93 • ©Honeywell Inc. 1993 • Form Number 68-0134

1 68-0134

T8624C,D
SPECIFICATIONS • ORDERING INFORMATION

Specifications

IMPORTANT: The specifications given in this publi-

cation 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.

TRADELINE® MODELS

TRADELINE models (see Table 1) are selected and

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

LIGHT-EMITTING DIODE (LED): SYSTEM LED

lights during thermostat ON cycle.
VOLTAGE RATING: 15 to 30 Vac.
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].

TABLE 1—TRADELINE MODELS.

Thermostat

Model

Number

T8624C 2 1 Auto HEAT-AUTO-COOL-OFF ON-AUTO Multistage
T8624D 2 2 Auto HEAT-AUTO-COOL-OFF ON-AUTO Multistage
T8624D 2 2 Manual HEAT-OFF-COOL ON-AUTO Multistage

Stages Changeover Switching

Heat Cool

Type

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

thermometer 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—factory-set at
6 cph; field-adjustable to 1,3,6 or 9 cph.

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

minimum off-time of five minutes.

FINISH: Beige matte with decorative brushed metal

faceplate or Premier White™.

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 dimensions.
TYPICAL KEYPAD: See Fig. 2.
ACCESSORIES:

TG586A Locking Cover.

TG512 Versaguard™ Universal Thermostat Guard.

System Fan

Application

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—

1. Model number. 3. System, fan switching desired.

2. Number of heat and cool stages desired. 4. Application.

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

Fig. 1—T8624 Subbase mounting dimensions in in. [mm].

13

1

16

[46]

5

5

16

[135]

5

3 [83]

16

3

4 [121]

4

M5181A

7 [179]

Fig. 2—Typical thermostat keypad.

4

[104]

T8624C,D

SPECIFICATIONS

31

1

32

[50]

3

32

SET
PRESENT
DAY/TIME

HOLD
TEMP

PROGRAM

HEAT/COOL

HEAT AUTO

RUN

DAY

SET

COOL

AM

WED

LEAVE

PERIOD

WAKE

SLEEP

OFF

LEAVE

RETURN

HEAT ON

TEMPERATURE

TIME

AHEAD

BACK COOLER

ON AUTO

ROOM

PRESENT

SETTING

WARMER

SYSTEM

SKIP

NEXT

PERIOD

CHANGE
TO LAST

PERIOD

FAN

M2998

3 68-0134

T8624C,D
SELECTION/APPLICATION

Selection/Application

The T8624 Thermostat uses the latest microelec­tronic design and control technology to provide home
and building owners with the highest level of comfort
available and optimal energy savings in a package that is
easy to use and easy to live with.

The following section is a guide to selection and
application of the best thermostat to meet individual
needs.

PROGRAMMING

Does the thermostat selected accommodate the
customer’s daily schedule, lifestyle or work schedule?

Device Programming

T8624C,D 5-1-1 (Mon-Fri,

Sat, Sun)

T8621A,C,D 7-day (each

day different)

T8600,01,02,03* 5-1-1 (Mon-Fri,

Sat, Sun)

The choices are:

*Model not currently available to control multistage

equipment.

IF NEW CONSTRUCTION APPLICATION, CON­SIDER:

• Equipment type (see manufacturer specifications).
—Staging required.
—System switching required.
—Fan switching required.

• Control wiring—number of conductors required

to operate equipment and thermostat.

IMPORTANT: The T8624 requires an additional con-

ductor to transformer common to provide continu­ous 24V power for thermostat operation.

IF RETROFIT/REPLACEMENT APPLICATION,
CONSIDER:

• Equipment requirements.
— Staging (heat stages, cool stages).
— System switching (manual: HEAT-OFF-COOL;

automatic: HEAT-AUTO-COOL-OFF). Emer­gency heat for heat pump application not pro­vided on T8624.

Daily

Temperature

Selection

4 heat and

4 cool

4 heat and

4 cool

4 heat and

4 cool

programmming and the override features that will best
suit the application? The choices are:

SINGLE-STAGE HEAT PUMPS

one option is to use a T8624C or D (see Fig. 8).
ing programmable thermostat. The T8624D is a two-

stage heating, two-stage cooling programmable thermo­stat. What both thermostats have in common is separate
W1 and W2 (first and second stage heat) terminals. In
both cases, the W1 can be used for changeover in heat­ing.

stage heating and first-stage cooling energized through
the Y terminal), simply jumper Y1 and W1.

cause the compressor to cycle on and off during recov­ery.

cool are set for hot water systems, the second stage of the
T8624 must be adjusted. Turn the cycle rate adjustment
screws to the hot water setting on both the T8624C and
D to achieve the cycle rate appropriate for heat pumps.

normally closed relay.
stage heat pumps.

— Fan switching; does fan come on automatically

from thermostat on cooling only (typical gas/
oil heating), or on call for cool and heat (typical
electric heat with single speed fan)?

• Existing wiring
— Are there enough conductors to operate the equip-

ment and the thermostat? Can a new cable be
pulled?

IMPORTANT: The T8624 requires an additional con-

ductor to transformer common to provide continu­ous 24V power for thermostat operation.

SECURITY

Does the thermostat selected provide access to

Access

Free access to
programming
and adjustment/
override.

Restricted
access to
device.

If home/building owner has a single-stage heat pump,
The T8624C is a two-stage heating, one-stage cool-

For single-stage compressor applications (both first-

Note that the recovery algorithm of the T8624 may

Although the cycle rate for the first stages of heat and

If changeover is utilized in the cooling mode, apply a
The above application should be used only on single-

Typical

Application Device

Home or
owner-occupied
commercial
building.

Public
building.

T8624A,C,D

T8624 with
TG512 Locking
Guard or
TG586A
Locking Cover.

4

RECYCLING NOTICE

If this control is replacing a control that contains
mercury in a sealed tube, do not place your old control in
the trash. Contact your local waste management author­ity for instructions regarding recycling and the proper
disposal of your old control.

If you have any questions, call Honeywell Inc. at 1­800-468-1502.

COMPATIBILITY

The T8624 Thermostats will replace most heating/
cooling system thermostats. As long as ac power is
continuously available to the transformer, the thermostat
will be compatible with any low-volt control system.

IMPORTANT: The T8624 requires an additional con-

ductor to transformer common to provide continu­ous 24V power for thermostat operation.

WHEN INSTALLING THIS PRODUCT…

1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazardous
condition.

2. Check the ratings given on the product to make
sure the product is suitable for your application.

3. Installer must be a trained, experienced service
technician.

4. Allow thermostat to warm to room temperature
before operating.

5. After installation is complete, check out product
operation as provided in these instructions.

T8624C,D

INSTALLATION

Installation

or disconnects. Remove any existing wallplate or sub­base from wall. To avoid miswiring later, label each
wire color with the letter or number on the wiring termi­nal as the wire is removed.

NEW INSTALLATION

Run cable to a hole at the selected wall location for the
thermostat, and pull about 3 in. [76 mm] of wire through
the opening. Color-coded, 18-gauge thermostat cable with
at least one conductor for each wiring terminal is recom­mended. Good service practice recommends selecting
cable with one or two more conductors than the immedi­ate application requires.

MOUNTING SUBBASE
IMPORTANT: Before mounting, set the system switch

to the OFF position.

NOTE: The subbase does not require leveling for proper

operation, but only for appearance.

Fig. 3—Removing thermostat from subbase.

CAUTION

!

Disconnect power supply to prevent electrical
shock or equipment damage.

LOCATION

Install thermostat and subbase about 5 ft [1.5m] above
the floor in an area with good air circulation at room
temperature.

Do not install thermostat where it may be affected by:

— drafts or dead spots behind doors, in corners or

under cabinets.

— hot or cold air from ducts.

— radiant heat from sun or appliances.

— concealed pipes and chimneys.

— unheated (uncooled) areas such as an outside wall

behind the thermostat.

REPLACING AN EXISTING THERMOSTAT

Turn off thermostat power at furnace or boiler. A two­transformer system may require turning off two switches

H

E

A

T

A

U

T
O

C

O

O

L

O
F

F

F
A

N

O

N

A

U
T

O

M 844

Remove thermostat from subbase (Fig. 3).

Mount the subbase directly onto the wall with the
screws and anchors included. If drywall construction,
use plastic anchors. Use the subbase as a template, and
with a pencil, mark the two mounting screw positions
(Fig. 4). Use
3/16 in. bit to drill holes for anchors. Gently tap anchors
into holes until they are flush with the wall surface.
Thread wires through the center opening of the subbase.
Then mount the subbase using the two screws provided.
Gently tighten the screws, level the top surface of the
subbase, and securely tighten the screws.

5 68-0134

T8624C,D
INSTALLATION

Fig. 4—Mounting subbase on wall.

WALL

WIRES THROUGH
WALL OPENING

WALL
ANCHORS
(2)

MOUNTING
HOLES

SUBBASE

MOUNTING
SCREWS (2)

M846

WIRING

All wiring must comply with local electrical codes

and ordinances.

Disconnect power before wiring to prevent electrical

shock or equipment damage.

The shape of the terminal barrier permits insertion of
straight or conventional wraparound wiring connections.
Either method is acceptable.

Push excess wire back into the hole, and plug the hole
with nonhardening caulk, putty or insulation to prevent
drafts from affecting thermostat operation.

NOTE: Restrict wiring to the recessed area surrounding

the terminals (Fig. 5) to assure thermostat/subbase

contact.

Refer to Figs. 6-8 for typical hookups of subbase and
thermostat.

ADJUSTING CYCLE RATE

To customize the thermostat cycling performance to
various types of heating equipment, cycle rate adjust­ment screws are provided on the back of the thermostat
to provide optimum room temperature control.

NOTE: Most applications will not require a change in

cycle rate.

The room air temperature will normally vary slightly
from the comfort temperature setting with the cycling of
the furnace or air conditioner.

The heating cycle rate of this thermostat is factory-set
for gas/oil warm air heating. The cooling cycle rate is
factory-set and cannot be adjusted. The heating cycle
rate can be adjusted by turning one or both cycle rate
adjustment screws located on the back of the thermostat.

Fig. 5—Restrict wiring to recessed area
surrounding terminals.

FOR STRAIGHT
INSERTION –
STRIP 5/16 in. [8 mm]

FOR WRAPAROUND –
RESTRICT
WIRING TO
THIS AREA

FRONT VIEW OF

TERMINAL AREA

WIRING TO BE BELOW
THIS SURFACE

CROSS-SECTIONAL VIEW OF

TERMINAL AREA

STRIP 7/16 in. [11 mm]

TOP SURFACE
OF SUBBASE

M 847

In multistage heat systems, the cycle rate adjustment
applies to the highest stage of heat only. Screws should
be backed out about one-half to one turn, or be turned in
until tight. See Fig. 9.

TIME/TEMPERATURE CONVERSION
(SOME MODELS)

The display readout may be converted between 12

and 24 hour clock or °C and °F using screws 2A and 2B
as indicated in Fig. 9.

FAN OPERATION OPTION SWITCH
(SELECT MODELS ONLY)

Select models include a fan operation option switch
on the subbase that is visible before the thermostat is
mounted on the subbase. The switch should be in electric
heat position for electric heating systems that do not
have independent fan control.

INSTALLING BATTERIES

Three AAA alkaline batteries are included to provide
backup to prevent program loss in case of power outage.
Install batteries in back of thermostat as shown in Fig.

10.

Without battery backup, the program will remain
about 30 seconds in event of power loss.

IMPORTANT: When batteries are first installed, the

display will flash 1:00 PM and 32°. The tempera­ture will stay at 32

°

F until the thermostat is

powered from the system wiring.

When the batteries are low, the display will flash
REPL BAT. Homeowner will have 20-30 seconds to
install new batteries after removing old batteries from
back of thermostat. After 20-30 seconds, it will be nec­essary to reprogram. REPL BAT indication will disap-

6

T8624C,D

INSTALLATION

Fig. 6—T8624C 2-stage heat/1-stage cool thermostat with HEAT-AUTO-COOL-OFF system and AUTO-ON
fan switching.

HEATING
TRANSFORMER

R

2

3

C

W1

W2

Y1

G

2

RC

HEAT RELAY 1

HEAT RELAY 2

COOLING
CONTACTOR

FAN RELAY

COOLING
TRANSFORMER

THERMOSTAT
LOGIC CIRCUIT

4

POWER
SUPPLY

SYSTEM
SWITCH

SUBBASE
LOGIC/
CONTROL
CIRCUIT

HIGH
LIMIT

HIGH
LIMIT

FAN
SWITCH

HEAT 1

HEAT 2

HEAT

AUTO

COOL

OFF

COOL

AUTO
ON

1

L1
(HOT)

L2

L1
(HOT)

L2

1

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.

2

FOR SINGLE TRANSFORMER SYSTEM JUMPER R AND RC.

3

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

4

DENOTES THERMOSTAT TO SUBBASE INTERCONNECTION.

M5233

7 68-0134

T8624C,D
INSTALLATION

Fig. 7—T8624D 2-stage heat/2-stage cool thermostat with HEAT-AUTO-COOL-OFF system and AUTO-ON
fan switching.

4

POWER
SUPPLY

THERMOSTAT
LOGIC
CIRCUIT

SUBBASE
LOGIC/
CONTROL
CIRCUIT

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.

FOR SINGLE TRANSFORMER SYSTEM, JUMPER R AND RC.

2

NOMINAL 24 Vac POWER MUST BE PRESENT BETWEEN

3

R AND C FOR THERMOSTAT OPERATION.

DENOTES THERMOSTAT TO SUBBASE INTERCONNECTION.

4

AVAILABLE ON T8624D MODELS ONLY.

5

HEAT

AUTO
COOL

OFF

SYSTEM
SWITCH

HIGH
LIMIT

FAN
SWITCH

AUTO

R

HEAT 1

HEAT 2

COOL 2

COOL 1

2

W1

2

3

C

W2

5
Y2

Y1

G

RC

COOLING
TRANSFORMER

HIGH
LIMIT

ON

L1
(HOT)

L2

HEATING
TRANSFORMER

HEAT RELAY 1

HEAT RELAY 2

COOLING
CONTACTOR 2

COOLING
CONTACTOR 1

FAN RELAY

L1
(HOT)

L2

M3765

1

1

8