Honeywell T8400C Thermostat User Manual

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T8400C and T8401C

Electronic Thermostats

INSTALLATION INSTRUCTIONS

The T8400C and T8401C Thermostats provide single-

INSTALLATION

stage, non-programmable temperature control for 24V

heating-cooling systems with manual changeover from

heat to cool. Heating cycle rate is selectable at 1, 3, 4, 5,

When Installing this Product…

, or 9 cph. Cooling cycle rate is fixed at 3 cph.

Read these instructions carefully. Failure to follow

them could damage the product or cause a hazard-

ous condition.

Check the ratings given in the instructions and on

the product to make sure the product is suitable for

your application.

Temperature indication can be set for °F or °C.

The T8400C Thermostat is powered through the heating/

cooling system controls. The T8401C Thermostat is

powered directly from the system transformer. Batteries

are not required because setpoints are held permanently

by non-volatile memory for all models.

Installer must be a trained, experienced service

technician.

All TRADELINE® models include a thermostat, wallplate

4. After installation is complete, check out product

(for wiring and mounting thermostat) and owner’s guide.

operation as provided in these instructions.

The T8400C SUPER TRADELINE® model also includes

two decorator cover plates for covering wallmarks.

CAUTION

Electrical Shock or Equipment Damage

Hazard.

Can shock individuals or short equipment

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.

circuitry.

Disconnect power supply before installation.

Contact your local waste management authority

for instructions regarding recycling and the

proper disposal of an old control containing

mercury in a sealed tube.

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.

U.S. Registered Trademark

69- 1480- 1

T8400C AND T8401C ELECTRONIC THERMOSTATS

YES

5 FEET

1.5 METERS]

[

M10308

Fig. 1. Typical location of thermostat.

The shape of the terminals permits insertion of straight or

wraparound wiring connections; either method is

acceptable. See Fig. 4.

Mounting Decorator Cover Plate and

Wallplate to Wall

IMPORTANT

The T8400C Thermostat is powered through the heating/

cooling system controls and is adaptable to most 4-wire,

18 to 30 Vac heating-cooling systems.

Level only for appearance. The thermostat func-

tions normally even when not level.

NOTE: Only SUPER TRADELINE® models have the

cover plate.

The T8401C Thermostat is powered directly from the

system transformer and is adaptable to most 5-wire, 18

to 30 Vac heating-cooling systems. Refer to Fig. 5 and 6

for typical wiring hookups.

Mount decorator cover plate (SUPER TRADELINE®

model only), wallplate, T8400C or T8401C, and the

screws provided (see Fig. 2) as follows:

5-3/4 IN. x 5-3/4 IN.

DECORATOR

Place the desired decorator cover plate and the

wallplate at the desired location on the wall.

Pull the thermostat wire through the entrance hole

on the decorator cover plate, then through the wall-

plate entrance hole.

COVER PLATE

WALL

Select the two mounting holes that best fit the

application.

Fasten the decorator cover plate and the wallplate

to the wall using the anchors and screws provided.

After wiring the wallplate, plug the hole to prevent

drafts from affecting the thermostat; see Wiring

section.

WALL

ANCHORS (2)

Wiring

IMPORTANT

Use an 18-gauge maximum wire for wiring the

T8400C and T8401C Thermostats.

All wiring must comply with local electrical codes and

ordinances. Disconnect the power supply to prevent

electrical shock or equipment damage.

3-7/8 IN. x 3-7/8 IN. DECORATOR COVER PLATE (SELECT MODELS).

DRILL 3/16 INCH HOLES (IF DRYWALL) OR 7/32 (PLASTER OR WOOD)

NOTE: To ensure proper mounting of thermostat,

restrict all wiring to the shaded area on the left

side of the terminals. See Fig. 3.

WHEN USING WALL ANCHORS.

M11041C

Fig. 2. Mounting decorator cover plate

and wallplate to wall.

69-1480-1

T8400C AND T8401C ELECTRONIC THERMOSTATS

KEEP WIRING IN

SHADED AREA

T8400C, T8401C

ALTERNATE MOUNTING

SCREW HOLE

COOLING

CONTACTOR

FAN

RELAY

MOUNTING

SCREW

HOLE

(HOT)

OIL PRIMARY

CONTROL

HOT)

(

24V

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

ALTERNATE

MOUNTING

SCREW HOLE

IN T8401C INSTALLATIONS, CONNECT C TERMINAL.

M11022B

Fig. 6. T8400C/T8401C heat-cool wiring

diagram in oil heating/electric cooling system.

Oil primary has its own transformer.

WIRING ENTRANCE HOLE

MOUNTING

M11023

SCREW HOLE

Mounting Thermostat to Wallplate

Fig. 3. Restrict wiring to shaded area.

Engage the tabs at the top of the thermostat and

wallplate.

Swing down the thermostat and press the lower

edge of the thermostat onto the wallplate to latch.

See Fig. 7.

DASHED LINES INDICATE TABS

ON BACK OF THERMOSTAT

FOR WRAPAROUND

STRIP 7/16 IN. (11 MM)

Set

Room

Set

Room

FOR STRAIGHT INSERTION

STRIP 5/16 IN. (8 MM)

FAN

Auto

SYSTEM

Cool Off Heat

FAN

Auto On

SYSTEM

Cool Off Heat

M11232

A ENGAGE TABS AT TOP

OF THERMOSTAT WITH

SLOTS ON WALLPLATE.

TERMINAL SCREW

Fig. 4. Wiring connections.

M18416

PRESS LOWER EDGE OF

CASE TO LATCH.

T8400C, T8401C

Fig. 7. Mounting thermostat wallplate.

COOLING

CONTACTOR

OPERATION

Setting FAN and SYSTEM Switches

FAN

RELAY

HEATING

PRIMARY

CONTROL

Fan and system settings are controlled manually by

using the switches located at the bottom of the

thermostat case. See Fig. 8.

HOT)

(

24V

FAN Switch

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND

OVERLOAD PROTECTION AS REQUIRED.

Fan switch settings are:

IN T8401C INSTALLATIONS, CONNECT C TERMINAL.

On: The fan runs continuously. Use for improved air

circulation and air quality.

M11021B

Auto: Normal setting for most homes. In cooling, the

fan starts and stops with the cooling equipment. In

heating, the fan is controlled directly by the heating

equipment and may start a few minutes after the

heating equipment turns on (on most systems).

When using an electric heat thermostat, the fan

starts and stops with the heating equipment.

Fig. 5. T8400C/T8401C heat-cool wiring diagram in

single transformer system with gas heat/electric

cooling.

69-1480-1

T8400C AND T8401C ELECTRONIC THERMOSTATS

Slide the FAN switch in the bottom left corner of the

thermostat to select the desired fan setting.

3. To increase the temperature setpoint press the s

key. Each press changes the setpoint one degree;

press and hold to change the setpoint several

degrees.

SYSTEM Switch

System switch settings control thermostat operation as

follows:

Cool: The thermostat controls the cooling system.

Off: Both heating and cooling are off.

Heat: The thermostat controls the heating system.

M14681

4. To decrease the temperature setpoint press the t

key. Each press changes the setpoint one degree;

press and hold to change the setpoint several

degrees.

Slide the SYSTEM switch in the bottom right corner of

the thermostat to select the desired system setting.

TEMPERATURE DISPLAY

M14682

Setting °F/°C Indication and Heat Cycle Rate

INCREASE

SETTING

NOTE: To save changes to the °F/°C indication and the

heat cycle rate, all seven steps must be com-

pleted.

Set

Room

DECREASE

SETTING

To set the °F/°C indication and heat cycle rate:

If the temperature is displayed in °F, set the tem-

perature setpoint to 52°F. If the room temperature

is displayed in °C, set the temperature setpoint to

11°C.

FAN

Auto On

SYSTEM

Cool Off Heat

FAN SWITCH

SYSTEM SWITCH

M18417

M14683

Fig. 8. Digital display and system

switches (FAN and SYSTEM).

OPTIONAL SYSTEM CHECKOUT

When in steps 2 and 3 only, the t key can be used to turn

heat or cool outputs on and off. Change the SYSTEM

switch setting to test heat or cool outputs. No action

takes place If the system switch is in the Off position.

Set Temperature Setpoint

NOTE: Temperature setpoint range is 40° to 99°F (5° to

7°C).

Examples:System setting at HEAT: If heat is on, the t

key turns it off; if heat is off, t turns it on.

The temperature setpoint and the room temperature are

shown separately on the digital display. The t indicator

points to Set when the temperature setpoint is displayed

and to Room when the room temperature is displayed

M14684

System setting at COOL: If cool is on, t key

turns it off; if cool is off, t turns it on.

INDICATOR

ROOM TEMPERATURE

Set

Room

SETPOINT TEMPERATURE

M14679

M14685

To set temperature setpoint:

Select Heat or Cool by sliding the SYSTEM switch

in the lower right corner of the thermostat to the

desired mode. See Fig. 8.

To display the temperature setpoint on the digital

display, press either the s or t key once. The tem-

perature setpoint is displayed for approxi-mately

five seconds as the indicator points to Set and

flashes.

2. Press the st keys simultaneously for more than one

second to light all segments on display and to enter

installer setup mode. When the keys are released,

a two-digit software revision code is displayed.

M14686

NOTE: In installer setup mode only, each press of the s

key momentarily displays 01. Each press of the

t key momentarily displays 02. When the keys

are released, these two-digit codes are no

longer displayed.

M14680

69-1480-1

T8400C AND T8401C ELECTRONIC THERMOSTATS

Press the s key. Factory information is displayed. A

typical example is shown, but information dis-

played varies by model. This information is for fac-

tory use only.

10. Press the s key to save all changes, exit installer

setup mode and return to normal operation.

NOTE: After exiting installer setup mode, change the

setpoint to the desired room temperature.

M14687

CHECKOUT

Press the s key again to display °C or °F.

Heating

Slide the SYSTEM switch to Heat and the FAN

switch to Auto, if available.

Press and hold the s key to raise the temperature

setting several degrees above the room tempera-

ture. After approximately ten seconds, the heating

equipment should start. In conventional systems,

the system turns on the fan through the use of a

time delay relay or through a limit control. When

using an electric heat thermostat, the fan starts

immediately.

M14688

Press the t key to change the °C or °F indication.

M14689

Press the s key to display the heat cycle rate of 1, 3,

, 5, 6, 9, or 12. If the desired cycle is displayed,

Press the t key to lower the temperature setting

below the room temperature. Heating equipment

should stop.

press the s key to exit the installer setup mode. To

change the heat cycle rate, press the t key to scroll

between 1, 3, 4, 5, 6, or 9. Stop scrolling when the

desired rate is displayed. See Table 1 for the cycle

rate options and the corresponding system equip-

ment.

Cooling

CAUTION

Low Temperature Hazard.

Operating at too low of an outdoor

temperature may cause compressor damage.

Do not operate cooling if outdoor temperature is

below 50°F (10°C). Refer to manufacturer’s

recommendations.

M14690

Table 1. Heating Cycle Rates.

System

Cycles Per Hour

Steam, radiant floor heat, gravity

1. Slide the SYSTEM switch to Cool and the FAN

switch to Auto.

Hydronic heat, condensing gas

_f_u_r_n_a_c_ea

Press the t key to lower the temperature setting

several degrees below the room temperature. After

approximately five minutes, the cooling equipment

should start. The fan starts and stops with the cool-

ing equipment.

Gas or oil forced air

Electric heat

Special applications^b

4, 5, 12

3. Press the s key to raise the temperature setting

above the room temperature. Cooling system

should shut down.

High efficiency furnace.

Refer to equipment manufacturer’s instructions.

NOTE: Steps 7 and 8 are available on select models.

NOTE: To bypass the 5 minute delay, see the Optional

System Checkout section.

Press the s key to display cooling algorithm config-

uration default.

Fan

Slide the SYSTEM switch to Off and the FAN

switch to On. The fan should run continuously.

Slide the FAN switch to Auto. In heating, the fan is

controlled directly by the heating equipment and

may start a few minutes after the heating equipment

turns on (on most systems). When using an electric

heat thermostat, the fan starts and stops with the

heating equipment. In cooling, the fan starts and

stops with the cooling equipment.

M18419A

Press the s key again to change cooling algorithm

to C1 or C3.

C1 = Standard cooling algorithm.

C3 = Aggressive cooling algorithm (can cause

overshooting).

Press the s key again. Current configuration (CC) is

displayed. A typical example is shown, but CC varies

by model. (This information is for factory use only.)

Make certain all equipment responds properly to the

thermostat.

M18420

69-1480-1

Automation and Control Solutions

Honeywell Honeywell Limited-Honeywell Limitée

985 Douglas Drive North

Golden Valley, MN 55422

35 Dynamic Drive

Scarborough, Ontario

M1V 4Z9

69-1480-1 G.H. Rev. 2-02

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