Lennox L3711C Operation Manual

OPERATION MANUAL

E2008 Lennox Industries Inc.

Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS

FOR FUTURE REFERENCE

L3711C 7−Day Programmable Thermostat

The Lennox ComfortSenset 3000 Series model L3711C
7-day programmable electronic thermostat provides
excellent temperature control and has a large,
easy-to-read display. This product includes a
programmable filter change reminder, an equipment
maintenance reminder, and a system check indicator to
notify the user when the equipment requires service.

Thermostat model L3711C is suitable for non−heat pump,
single-stage heat/single-stage cool applications with either
gas or electric furnace. Also, the thermostat provides auto­changeover capability.

ComfortSenset 3000 Series
Model No. L3711C 7-Day
Programmable Thermostat

CONTROLS

506072−01
02/08
Supersedes 505,067M

Table of Contents

7−Day Programmable Thermostats 1. . . . . . . . . . . . . . .

General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . .

Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . .

DAY/TIME − Set Day and Time 2. . . . . . . . . . . . . . . . . .

HEAT − Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . .

COOL − Cool Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . .

AUTO − Using the Autochangeover Mode 3. . . . . . . . .

HOLD − Temperature Hold Mode 4. . . . . . . . . . . . . . . .

PROG − Thermostat Programming 4. . . . . . . . . . . . . . .

COPY − Copy a Program 5. . . . . . . . . . . . . . . . . . . . . . .

FAN − Controlling Fan Operation 5. . . . . . . . . . . . . . . . .

Displaying Outside Temperature 5. . . . . . . . . . . . . . . . .

SETTINGS − Filter /Maintenance Reminder 5. . . . . . .

Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . .

Removing/Installing Thermostat 6. . . . . . . . . . . . . . . . .

Default Thermostat Settings 6. . . . . . . . . . . . . . . . . . . .

Thermostat Output Table 7. . . . . . . . . . . . . . . . . . . . . . .

Technical Specifications 7. . . . . . . . . . . . . . . . . . . . . . . .

Litho U.S.A.

General

These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.

Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox model
L3711C thermostat. Refer to the installation manual for in­structions regarding installation and wiring of the thermo­stat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis­play will appear as shown in figure 1.

Copy tofrom

PROG

A B C D

HOLD

FAN ON
AUTO

FILTER

MAINTENANCE

OUTROOM

i88

Figure 1. Initial Power−Up Display

All display segments are momentarily activated. This oc­curs as a normal part of thermostat initialization.

MO TU WE TH FR SA SU

AM

I8:88

PM

COOL SETPOINT

SERVICE

88

HEAT SETPOINT

°

88

°

COOL

OFF

AUTO

EMG.
HEAT

°

Hi
Lo

02/08 506072−01

*2P0208* *P506072-01*

Within a few seconds, the HOME screen appears (see fig­ure 2) with default settings as shown. After about 1 minute
of initialization time, the actual room temperature will be
displayed.

PROG
A B C D

HOLD

FAN ON
AUTO

MO
AM

PM

ROOM

I0:26

COOL

AUTO

°

EMG.
HEAT

OFF

70

Figure 2. Home Screen

At this point, the thermostat will be fully functional; its de­fault temperature setpoint (not shown) is 70°F. At this
point, if the equipment has been fully powered and if a heat
demand were present, the system would begin operating.

NOTE − Temperature scale default is Fahrenheit units but
may be reset to show Celsius, if desired. See page 7.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right−
hand side of the thermostat (see figure 3).

IMPORTANT

Do NOT begin pressing buttons until after you read
the following section describing each button.

A pale blue display backlight illuminates for 30 seconds
each time any button is pressed.

When the PROG or DAY/TIME button is pressed, a field
begins flashing, expecting another input. Start making
changes within 15 seconds or the HOME screen will re­turn.

Heat

Cool

Prog

Auto

Day/Time

Copy

(DOOR

Fan

Settings

Hold

Enter

(Outside)

OPEN)

Figure 3. Thermostat Buttons

When an Arrow, HOLD, HEAT, or COOL button is pressed,
SETPOINT and the temperature setting appears for 15
seconds. If desired, start making changes within 15 sec­onds or the HOME screen will return. The backlight will
turn off 15 seconds after the HOME screen reappears.

DAY/TIME − Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour,
minute, and day of week as follows:

1. AM12" will flash on the screen. Press the UP/DOWN
arrows to change the hour. (AM" or PM" must corre­spond to time of day.) Press the DAY/TIME button OR,

if adjusting for daylight savings time, pressing the EN­TER button stores the single change and exits to the
HOME screen, bypassing minutes and day of week.

2. Minutes will flash. Use the UP/DOWN arrow button to
display the minutes past the hour. Press the DAY/
TIME button.

3. Day MO" (Monday) will flash. Use UP or DOWN arrow
buttons to display the current day. Day selections are
abbreviated as MO, TU", WE", TH", FR", SA",
and SU". Press the DAY/TIME button.

4. The HOME screen reappears; confirm day and time
are correct. This completes day and time setting.

506072−01 02/08

Page 2

HEAT − Using the Heat Mode

COOL − Using the Cool Mode

Enabling and Disabling Heat Mode

The thermostat must be in the heat mode to control the
heating equipment. Press the HEAT button to enable or
disable heat mode. If the thermostat is in cool or off mode,
pressing the HEAT button enables the heat mode (indi­cated by HEAT in the lower right corner − see figure 4).

Heat

Cool

Prog

Auto

5:30

Day/Time

Copy

82

(DOOR

°

°

OPEN)

OFF

HEAT

Fan

Settings

Hold

Enter

(Outside)

70

66

Figure 4. Turn Heat ON/OFF

If the thermostat is in heat mode, heat mode is disabled
when the HEAT button is pressed. This is indicated by OFF
near the right side of the display as shown in figure 5.

ROOM

75

°

HEAT SETPOINT

75

Figure 5. Heat/Cool Mode Disabled

Heating Demand

Set the thermostat to heat mode to control the heating
equipment. Then, if the room temperature is lower than the
temperature setpoint, as shown in figure 6, the thermostat
detects a heating demand and will activate the heating
equipment to satisfy the demand.

ROOM

72

°

HEAT SETPOINT

75

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode as
desired. If the thermostat is in heat or off mode, cool mode
is enabled when the COOL button is pressed. This is indi­cated by COOL on the right side of the display (see figure

7).

Heat

Cool

Prog

Auto

i0:30

Day/Time

Copy

70

(DOOR

Fan

Settings

Hold

Enter

(Outside)

75

66

Figure 7. Turn Cool ON/OFF

If the thermostat is in cool mode, pressing the COOL but­ton disables cool mode (indicated by OFF, similar to figure

5).

Cooling Demand

Set the thermostat to cool mode to control the cooling
equipment. Then, if the room temperature is higher than
the temperature setpoint, as shown in figure 7, the thermo­stat detects a cooling demand and will activate the cooling
equipment to satisfy the demand.

Cooling operation is indicated by flashing snowflake"
icons in the display. When the actual temperature drops
below the temperature setpoint, the snowflake icons will
disappear. This indicates that the cooling demand has
been satisfied and that the cooling equipment has been
turned off.

NOTE − If no buttons are pressed during a demand for
cooling, the equipment must operate for at least 4 minutes.
After a demand has been satisfied, cooling equipment op­eration is locked out for 5 minutes. If another cooling de­mand occurs during this 5−minute interval, COOL" and the
snowflakes will flash; however, the cooling equipment will
not operate until the 5−minute delay has elapsed.

NOTE − The cooling setpoint cannot be lower than the
heating setpoint. Also, the difference between the cooling
and heating setpoint must be at least 4 degrees.

AUTO − Using the Autochangeover Mode

OPEN)

Figure 6. Heating Demand

Heating operation is indicated by a flame icon in the lower
right corner. When the actual temperature rises above the
temperature setpoint, the flame icon will disappear. This
indicates that the heating demand has been satisfied and
that the heating equipment has been turned off.

NOTE − Heating equipment is activated for at least 3 min­utes if no buttons are pressed during the demand interval.

When in either heat mode or cool mode, autochangeover
can be enabled or disabled by pressing the AUTO button. If
enabled, AUTO appears at the lower right corner of the dis­play. The thermostat will then automatically change over
from heating to cooling and vice versa, to keep the room
temperature in between the heating and cooling setpoints.
Autochangeover can be used in either of the thermostat
hold modes, or when the thermostat program is running.
These modes are described later.

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L3711C 7-DAY PROGRAMMABLE THERMOSTAT