Honeywell T8400C1099, T8401C1031 User Manual

T8400C1099, T8401C1031

Electronic Thermostats

The T8400 and T8401 Thermostats provide single-stage,
non-programmable temperature control for 24V heating­cooling systems with manual changeover from heat to
cool. Heating cycle rate is selectable at 1, 3, 4, 5, 6, 9, or
12 cph. Cooling cycle rate is fixed at 3 cph. Temperature
indication can be set for °F or °C.

The T8400 Thermostat is powered through the heating/
cooling system controls. The T8401 requires a common
wire for operation. Batteries are not required because
setpoints are held permanently by non-volatile memory.

The T8400 and T8401 models include a thermostat,
wallplate (for wiring and mounting thermostat) and
owner’s guide.

MERCURY 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 an old control containing
mercury in a sealed tube.

INSTALLATION

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 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
operation as provided in these instructions.

INSTALLATION INSTRUCTIONS

CAUTION

Electrical Shock or Equipment Damage
Hazard.
Can shock individuals or short equipment
circuitry.

Disconnect power supply before installation.

Location

Install the thermostat about 5 ft (1.5m) above the floor in
an area with good air circulation at average temperature.
See Fig. 1. Do not install 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.

This thermostat is a precision instrument and was
carefully adjusted at the factory. Handle it carefully.

Mounting Wallplate to Wall

IMPORTANT

Level only for appearance. The thermostat func­tions normally even when not level.

Mount the T8400 and T8401 with the screws provided
(see Fig. 2) as follows:

1. Place the wallplate at the desired location on the
wall.

2. Pull the thermostat wire through the entrance hole
on the wallplate.

3. Fasten the wallplate to the wall using the anchors
and screws provided.

4. After wiring the wallplate, plug the hole to prevent
drafts from affecting the thermostat; see Wiring
section.

® U.S. Registered Trademark
Copyright © 2002 Honeywell • • All Rights Reserved

69-1484-2

T8400C1099, T8401C1031 ELECTRONIC THERMOSTATS

M12202A

M12580

FAN OPERATION (FUEL) SWITCH

NO

WALL

MOUNTING
SCREWS (2)

1

WHEN USING WALL ANCHORS, DRILL 3/16 INCH
HOLES FOR DRYWALL, 7/32 INCH HOLES FOR
PLASTER OR WOOD.

WALL
ANCHORS (2)

1

WALLPLATE

Fig. 2. Mounting wallplate to wall.

YES

NO

5 FEET

[1.5 METERS]

Fig. 1. Typical location of thermostat.

Wiring

IMPORTANT

Use an 18-gauge maximum wire to wire the
T8400 and T8401 Thermostats.

All wiring must comply with local electrical codes and
ordinances. Disconnect the power supply to prevent
electrical shock or equipment damage.

NOTE: To ensure proper mounting of thermostat,

restrict all wiring to the shaded area. See Fig. 4.

The shape of the terminals permits insertion of straight or
wraparound wiring connections; either method is
acceptable. See Fig. 5.

Refer to Fig. 6 through 10 for typical wiring hookups.

NO

M11338

Setting Fan Operation (Fuel) Switch

The fan operation (fuel) switch is preset at the factory in
the F position. See Fig. 3. This is the correct setting for
most systems. If this system is an electric heat system,
set the switch to the E position. The E setting allows the
fan to turn on immediately with the heating or cooling
equipment in a system where the G terminal is
connected.

69-1484-2 2

E

F

Fig. 3. Fan operation (fuel) switch.

T8400C1099, T8401C1031 ELECTRONIC THERMOSTATS

)

A

T)

L
(

L

L
(

L

0

KEEP WIRING IN
SHADED AREA

G

Rc

R

W

Y

MOUNTING
SCREW HOLE

WIRING ENTRANCE
HOLE

Fig. 4. Restrict wiring to shaded area

(T8400C1099 shown).

FOR STRAIGHT INSERTION
TERMINAL
SCREW

STRIP 5/16 IN. (8 MM)

G

Rc

B

O

MOUNTING
SCREW HOLE

M16432

FOR WRAPAROUND
STRIP 7/16 IN. (11 MM

G
Rc

2

R
W

Y

1

L1
(HOT)

L2

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

1

OVERLOAD PROTECTION AS REQUIRED.
FACTORY INSTALLED JUMPER.

2

Fig. 6. Typical hookup of T8400C1099 in heat-cool

1
1

HOT)

2

COOLING
TRANSFORMER

1

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

2

REMOVE RC TO R JUMPER WHEN INSTALLED ON A TWO TRANSFORMER
SYSTEM.

3

CAN BE USED FOR CHANGEOVER VALVE ON SINGLE-STAGE HEAT
PUMP SYSTEMS.

4

POWER TO R TERMINAL IS REQUIRED WHEN THE SYSTEM SWITCH IS IN
THE OFF POSITION.

Fig. 7. Typical hookup of T8400C1099 in heat-cool

B
O

HEATING
PRIMARY

24V

CONTROL

system with single transformer.

G

Rc

R

2

W
Y

3

FAN

COOL

RELAY

DAMPER

COMPRESSOR
CONTACTOR

HEAT
RELAY

system with two transformers.

4

B
O

HEAT
DAMPER

3

FAN
RELAY

COOLING
CONTACTOR

M13275

HEATING
TRANSFORMER

M12562

1

L1
(HO

L2

R

W

B

Y

Fig. 5. Wiring connections

(T8400C1099 shown).

O

M13274

HOT)

TRANSFORMER

Fig. 8. Typical hookup of T8400C1099 in single-stage

G

Rc

3

R

W

4

Y

1

1

2

1

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

CAN BE USED FOR CHANGEOVER VALVE ON

2

SINGLE-STAGE HEAT PUMP SYSTEMS.

3

FACTORY INSTALLED JUMPER.

4

FIELD INSTALLED JUMPER.

COMPRESSOR

24V

2

B

2

O

heat pump systems.

HEAT
CHANGEOVER

COOL
CHANGEOVER

FAN
RELAY

M2088

3 69-1484-2