Honeywell T7400 User Manual

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Con~raiulations!
You are the owner of on&of the finest thermostats
t?“w produced by Honeywell.

The unique features of the T7400 Programmable
Commercial Thermostat,satisfy the special
requirements of commercial single zone aif

conditioning systems, and provide convenience and
temperature control accuracy that is un~oralleled in
the industrv n7is thermostat also includes enerav
saving feaiures which allow it to minimize the &rgy

needed to maintain comfort conditions by using

outdoor air for ‘We” cooling whenever possible.
A thorough review of this Owner’s Guide will help you

identify those features which will maximize comfoit,
convenience and savings in your application.

Terms and words that may not be familiar to you are
explained in the glossary at the end of this guide.

STARTUP

When power is first applied, an internal startup

prcgrom begins. This reauires 1 minute to complete.
and takes place after any total loss of power (supply

voltage and backup battery).
During this titie, default temperature set point values

exe used for temperature control. These CIIC: heating
68 F (20 C]. economizer 72 F (22 C), and cooling 78 F
(26 C]. Following the statiup period. you can enter
new set points which will @e ,used in place of these

default values.
Should a power failure occur after your time and

temperature schedule entries are made, the backup

battery will maintain your schedule. As long as either
system or battery backup power is present, your
program is available and will be used for’
temperature control.

OPERATION

IMPORTANT:
Note that the T7400 svstem will not read
instonton~usly to s&t point changes. Except os

mentioned below, the minimum stage on- and otf-

times will oIwoys be followed. Although the
temperature control monitoring occurs constantly,
the temperature display updates approximately
every 2 minutes unless the ROOM TEMPERATURE key is
depressed.

The temperature control program takes effect after
the startup period. If space temperature is far below
set point, CI stage of heat could turn on within 1
minute of startup. This is the only exception to the
heating minimum off-time of 2 minutes.

If mechanical cooling is called for. the minimum off­time of 4 minutes will elapse after the 1 minute
startup period (5 minutes total).

MINUTES

1 COOLING 1 HEATING 1

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Fig. 1 -Thermostat cycle timing illustrations

OPERATIONAL

xe temizerature = 70 F; heat 1

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MINUTES

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POWER-UP

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0 . Power on (1 st applied or after ioss of

supply voltage and backup

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battery.

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PROGRAM SCHEdJCE

Each day of the week ccl” be individually
programmed with an Occupied and an Unoccupied
period to make maximum use of schedule variations.
In addition to the Occupied and Unoccupied mode

of thermostat operation. there is CI third mode called

Intelligent Recovery”.
Occupied operation is based on 3 set points: heat.

economizer. and cool. Unoccupied operation is
based on 2 set points: heating and cooling. l%he

economizer is operational during the Unoccupied

period, but at a s&point fixed at 3 F (2 C) helow the
Unoccupied cool set point.

Fig. 2-17400 program schedule and temperature control.

Intelligent Recovery’“, based on CI set point ramping

feature, is used when switching from Unoccupied
operation to Occupied operation. This selves energy

by varying switchover time depending on
prevailing weather conditions. The time used to
achieve the occupied set point is the shortest
possible time that will still ensure comfort conditions
are reached by the occupied stat time.

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Convenient keyboard layout provides effortless

program entry. .youi avenue to maximum energy

and cost savings.
The following pages provide function-by-function

instructions to progrcrr the T7400 Programmable
Commercial Thermostat.

The following general steps are required to enter your
weekly time and temperature schedule into the
T7400. See the pages indicated for detailed

programming instructions.

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Enter the correct time and day.
(3ee pages 14 through 17.)

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Enter the temperature set points you want for programming step. ~For example. to review the
heating. economizer, and cooling system

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To review program entries. simply press the
same function keys used to begin each

ECONOMIZER temperature set point, press the

operation. ECONOMIZER key.

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(See pages 18 through 27.)

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For each day of the week. enter starting time for

For sample schedules and their programs. see
pages 32 through 37.

the periods when your building will be
occupied and unoccupied. (See pages 28
through 31.)

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SELECTING~HE DESIRED OPERATING

DISPLAY

. PRESENT TIME and ROQM TEMPERATURE keys

•~ If neither key is pressed, T7400 will automatically

(Optional)

allow you to select c@tinuous display of time or
temperature. respectively.

revert to a display of,,present time within 2
minutes of the last keypress.

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T7400 will default to Occupied mode and
control to respective Heat, Economizer. and
Cool set points of 68 F. 72 F, and 78 F until
thermostat is reprogrammed.

LOSS Of External Power

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Blinking display of time or temperature

indicates loss of external power. The backup
botteiy maintains your time and temperature
schedule during the power loss.

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Keyboard and red indicator lights exe

inoperative while the 77400 is on batteN power

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PROBLEM INDICATORS

Loss of Stored Program

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Blinking display of 3 dashes (- -) indicates 10%
of stored program. (Three steady dashes

represent an occupied or unoccupied time slot
that is not programmed.)

TEMPORARILY OVERRIDING THE
17400’s PROGRAM

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3 HOUR OCCUPIED key allows you to <activate
the temperature set points programmed for
your building’s occupied period for 3 hours.

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‘Once pressed. the 3 HOUR OCCUPIED key can

be pressed again to cancel this command,

and return the T7400 to program control.

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CONTINUOUS UNOCCUPIED key allows you to
activate the temperature set points
programmed for your building’s unoccupied
period for an indefinite time.

(optional)

Failure of Temperature Sensor

. While in the ROOM TEMP display mode. 0

display of (- “) indicates failure of wiring or
the temperature sensor.

. System will safely deenergize all heating and

cooling stages if cI sensor failure occurs.

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pressed. the CONTINUOUS UNOCCUPIED

key must be pressed again to cancel this
command, and return the 17400 to piogiam
control.

The 3.HOUROCCUPIED and

CONTINUOUS UNOCCUPIED keys cannot be
used at the same tir&The last key pressed will
be in control.

Red indicators near the display window show
when 3 HOUR OCCUPIED and
CONTINUOUS UNOCCUPIED ovenide
functions are activated.

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