Lennox ComfortSense L7742U User guide

05/09 506228−01
*2P0509* *P506228-01*
E2009 Lennox Industries Inc.
Dallas, Texas, USA
Shipping and Packing List
1 − ComfortSense
®Model L7742U touch screen, 7−day program-
mable thermostat
2 − Mounting screws (M3.5x25mm self−tapping screws)
2 − Wall Anchors
1 each − Installation Quick-Start Guide, Programming & Application
Guide, Homeowner’s Manual, Warranty card, Warranty Audit tag
PROGRAMMING AND
APPLICATION GUIDE
ComfortSense®7000 Series
Model L7742U Touch Screen Programmable Thermostat
CONTROLS
506228−01
05/09
Supersedes 04/09
IMPORTANT
Read this manual before programming the thermostat.
Use this thermostat only as described in this manual.
IMPORTANT
In all applications, the ComfortSense®Model L7742U thermo-
stat can only be used with all residential units and approved
commercial split-system matches, and those which meet the
following installation criteria:
Sinstallation uses 18 GAUGE thermostat wire or larger,
Sthermostat wire run length DOES NOT EXCEED 300’ (91m),
Sload from any thermostat connection is 1 AMP or LESS.
If used with Harmony II®Zone Control System, consult Applica-
tion Note H−04−5.
Litho U.S.A.

506228−01 05/09 Page 2
Table of Contents
ComfortSense
®Model L7742U Thermostat 3. . . . . . . . . . . . .
Features 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Touch Screen Display 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Home ScreenCurrent Conditions & Temp. Settings 5. . . . .
Controlling the Heat/Cool Modes of Operation 6. . . . . . . . . . .
Controlling the Fan Operation 7. . . . . . . . . . . . . . . . . . . . . . . . .
Controlling the Schedule 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Schedule TabProgramming 8. . . . . . . . . . . . . . . . . . . . . . . . .
Options TabReminders & User Settings 10. . . . . . . . . . . . . . .
Options TabInstaller Settings 13. . . . . . . . . . . . . . . . . . . . . . . .
Resetting Program to Factory Conditions 16. . . . . . . . . . . . . . .
EPA ENERGY STAR®Recommended Setpoints 17. . . . . . . . .
Humidification 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dehumidification 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Humiditrol
®Enhanced Dehumidification Accessory (EDA) 22.
Stage Delay and Differential Settings 24. . . . . . . . . . . . . . . . . . .
Temporary Temperature Change (Pausing the Schedule) 31. .
Optional Remote Outdoor Sensor 32. . . . . . . . . . . . . . . . . . . . . .
Service Reminders 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit Part and Serial Numbers 33. . . . . . . . . . . . . . . . . . . . . . . . .
Memory Protection 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix A. Flow Diagrams & Wiring Diagrams 34. . . . . . . . . .
Appendix B. Diagnostic Info. & Available System Settings 39.
NOTE − This thermostat is equipped with automatic compressor
protection to prevent potential damage due to short cycling or extended
power outages. The short cycle protection provides a 5−minute delay
between heating or cooling cycles to prevent the compressor from be-
ing damaged.
CAUTION
This is a 24VAC low−voltage thermostat. Do not install on volt-
ages higher than 30VAC.
Do not short (jumper) across terminals on the gas valve or at the
system control to test installation. This will damage the thermo-
stat and void the warranty.
WARNING
Always turn off power at the main power source by switching
the circuit breaker to the OFF position before installing or re-
moving this thermostat.
All wiring must conform to local and national building and elec-
trical codes and ordinances.
Do not switch system to cool if the outdoor temperature is be-
low 45°F (7°C). This can damage the cooling system.
These instructions are intended as a general guide and do not super-
sede local codes in any way. Consult authorities having jurisdiction be-
fore installation.
Check thermostat for shipping damage. If you find any damage, imme-
diately contact the last carrier.

Page 3 ComfortSensetModel L7742U Touch Screen 7−Day Programmable Thermostat
ComfortSense®Model L7742U Thermostat (Catalog No. Y2081)
Description
The ComfortSense®Model L7742U thermostat is an electronic 7−day
universal multi-stage programmable touch screen thermostat. It also
offers enhanced capabilities which include:
Shumidification measurement and control,
Sdew point adjustment control,
Sdehumidification measurement and control,
SHumiditrol
®Enhanced Dehumidification Accessory (EDA) capa-
bility,
Sequipment maintenance reminders,
Sworry−free memory storage feature,
Smenu−driven display.
This thermostat supports heat pump units or non−heat pump units, with
up to 4 stages of heating (dual fuel units) and 2 stages of cooling.
Dimensions
Screen dimensions: 3−7/16" (87 mm) width x 2−9/16" (65 mm) height
Case dimensions: 5−7/8" (149 mm) width x 4−9/16" (116 mm) height x
1−1/4" (31mm) depth
Features
Compressor Short Cycle Protection
A 5−minute compressor short cycle protection timer begins when a
compressor output is de−energized. Also, if a power loss occurs, the
system will go into compressor protection mode and display WAIT in
the display if there is a cooling or compressor heating call.
Outdoor Temperature Sensor
An outdoor temperature sensor (X2658) is required for dual fuel ap-
plications, balance points, dew point humidity control, and with Humidi-
trol®EDA.
In addition to measuring and displaying outdoor temperature, the out-
door sensor provides dew point adjustment and control for all models. If
used with this thermostat, the sensor enables optimal heating equip-
ment operation via programmable balance points.
NOTE − The outdoor sensor uses standard thermostat wiring; it
may be wired using two wires of a multi−wire cable.
When the outdoor sensor is connected, the temperature can be dis-
played in the information display area (see figure 2).
NOTE − For proper operation of Humiditrol®EDA applications, the out-
door sensor (X2658) MUST be installed.
L" Input
L" input from the equipment is used to notify the user of an outdoor
equipment fault by displaying HVAC ERROR DETECTED" when one
of the following conditions exist:
SL" terminal is activated with 24VAC and Y1 has been activated
for 5 minutes (units without LSOM, but which use Service Light
Monitor Kit), OR,
SLSOM error signal is detected on L" input and Y1 has been acti-
vated for 5 minutes.
NOTE − The L input is used for diagnostic information purposes only, it
is not intended to provide equipment protection.

506228−01 05/09 Page 4
Touch Screen Display
A
B
C
G
I
H
F
E
D
E
Figure 1. Touchscreen display
Press the screen anywhere − the first press turns on the backlight.
A Selection Tabs − Press to select: HOME (normal display),
SCHEDULE (for programming), OPTIONS (to set fan operation,
alerts, service reminders, and other user and installer settings).
B MODE − press to cycle through HEAT, COOL, AUTO
(autochangeover),OFF, EM HEAT (emergency heat).
C SCHED (schedule) − press to change between ON and OFF.
DDisplays room temperature.
EDisplays the current operation SET AT point(s). If MODE is set to
AUTO (autochangeover), both HEAT and COOL setpoints are
displayed.
FUp/down arrows used for adjusting temperature up or down; if in
AUTO (autochangeover) mode, two sets of up/down arrows ap-
pear.
GInformation display area, displays different information depending
on the tab selected:
DHOME tab: displays outdoor temperature (if outdoor sen-
sor X2658 is installed), indoor relative humidity (RH),
which mode is calling, hold settings information, service
reminders.
DSCHEDULE tab: displays the event being programmed;
DOPTIONS tab: displays a scrolling list of installer- and
user−adjustable parameters, including filter and service
reminder periods, etc.
HSchedule time adjustment, User/Installer Settings up/down ar-
rows:
DHOME screen: not visible except when executing a HOLD
SETTING)
DSCHEDULE and OPTION screens: used to adjust sched-
ule and option settings.
IDynamic keys − not visible in HOME screen unless executing a
HOLD SETTING. For SCHEDULE and OPTIONS settings, these
keys appear and change depending on the selection. See the
schedule and options sections for details.

Page 5 ComfortSensetModel L7742U Touch Screen 7−Day Programmable Thermostat
Home ScreenCurrent Conditions & Temperature Settings
INFORMATION
DISPLAY AREA
COOLING
TUE OCT 23 1:15PM
Figure 2. Home Screen
The HOME screen (figure 2) displays indoor temperature and outdoor
temperatureif the outdoor sensor is installed. Other system operational
information,such as indoor relative humidity (if turned on in user set-
tings), dehumidifying, cooling or heating, will alternately be displayed in
the information display.
Equipment operation information appears in the boxes along the left
side of the home screen to indicate cooling or heating equipment opera-
tion setting, and whether scheduled programming is ON or OFF. From
these boxes, users can change the unit’s mode to HEAT, COOL, AUTO
(autochangeover− default), EM HEAT (emergency heat for heat pump
applications including dual fuel and HP with Electric Heat), or OFF.
The user can also decide whether to operate the unit per the program-
mable schedule, or in a non−programmable mode using the SCHED
box.

506228−01 05/09 Page 6
Controlling Heat/Cool Modes of Operation
On initial power up or after an a power loss over 2
hours, the thermostat powers up at the HOME
screen in the AUTO position. If it powers up after a
power loss of less than 2 hours, it assumes the last
mode set. Pressing MODE repeatedly scrolls
through all the modesAUTO, EM HEAT, COOL,
HEAT, then back to OFF.
HEAT, COOL and OFF modes are as each name implies. AUTO
(autochangeover) allows the thermostat to switch between Heating
and Cooling, whichever mode is dictated by the indoor temperature.
EM HEAT (emergency heat) bypasses the first stage of heating (any
stage[s] of heat pump heating) and goes directly to the heat stage used
for maximum heating to more quickly warm a very cold house.
When the indoor temperature decreases or increases, the HEATING or
COOLING cycle will turn on based on the displayed mode. When the
HVAC system is on, the INFORMATION DISPLAY AREA (shown in fig-
ure 3) will display one or several operational messages (listed in the
table below). If the outdoor sensor is connected and is turned on in user
settings, outdoor temperature will be included in the displays. The table
below summarizes the information messages.
When the faults, errors, and service information displays appear, dy-
namic keys will appear under the second line entries, REMIND,
CLEAR, SERVICE, or RESET. Press the box to perform the action.
INFORMATION DISPLAY AREA
Figure 3. Home Screen
Information Display Area table
Faults, Errors, and Service Information Operating Information
TEMP SENSOR ERROR, MEMORY ERROR
CALL FOR SERVICE
Top line: fault/error
Bot. line: action
SET DATE/TIME
Default DATE/TIME (MON JAN 1 12:00 PM)
[First time start up msg]
NO OUTDOOR SENSOR
CALL DEALER INFO
Top line: fault/error
Bot. line: action
HEATING, COOLING, HUMIDIFYING, DEHUMIDIFYING,
SYSTEM OFF, OUTDOOR TEMP xxF, INDOOR RH xx%,
MON SEP 24 3:OO PM
Top line: operation msgs
Bottom line: date & time
REPLACE: MEDIA FILTER; UV LAMP; HUM PAD; METAL INSERT
REMIND RESET
Top line: serv. req’d
Bot. line: action
SCHEDULE ON, SCHEDULE OFF, WAIT, FAN ON, FAN CIRC
MON SEP 24 3:OO PM
Top line: operation msgs
Bottom line: date & time
ROUTINE SYS CHECK−UP
REMIND RESET
Top line: serv. req’d
Bot. line: action
HOLD SETTING UNTIL PRESS SCHED TO
MON SEP 24 3:OO PM RESUME PROGRAM
[Alternating msgs during
a held schedule]
NO OUTDOOR SENSOR, HUM SENSOR ERROR, HVAC ERROR DETECTED
REMIND SERVICE
Top line: fault/error
Bot. line: action
DEALER INFORMATION (Edited to show dealer contact informa-
tion [2 lines])
Contact
Installing Dealer

Page 7 ComfortSensetModel L7742U Touch Screen 7−Day Programmable Thermostat
Controlling the Fan Operation
Fan Modes
If backlight is not on continuous, press the screen
anywhere to turn on the backlight. Press the
OPTIONS tab to access the FAN mode control.
Press FAN button; repeated presses scroll through
all the modes, AUTO, ON, and CIRC (circulate).
SAUTOthe fan is following schedule.
SONthe fan is NOT following the schedule and runs continuously
until it is changed from the OPTIONS screen.
SCIRCthe fan is following schedule and cycles during periods of
equipment inactivity. Cycle time is dependent on user settings
FAN CIRCULATE (Page 11).
If FAN mode displays AUTO and ON or CIRC was selected during
scheduling for the current period, the thermostat will indicate the current
fan mode in the information display (FAN ON or FAN CIRC).
In the CIRC mode, the user can cycle the fan for a programmed
percentage of active time per hour, during periods of equipment
inactivity (i.e., heating or cooling equipment not running). The fan is ON
for 5 minutes at a time. The user may change the percentage of ON time
that the fan is on (see FAN CIRCULATE [Page 11]):
Fan Program
The user can program the fan to be ON, AUTO, or CIRC during a
program event period. While scheduling the event, if the fan is set to
ON, it will remain on during the entire event. If it is set to CIRC, it will
circulate during equipment inactivity per user programmable cycles
(see FAN CIRCULATE, Page 11). If set to AUTO, the fan will come on
with the equipment to serve the heating/cooling demand and go off
accordingly.
NOTE − When the OPTIONS screen FAN mode is changed to ON or
CIRC, whatever was scheduled is ignored − the fan will either be ON or
it will CIRCULATE per the user−programmed intervals (USER
SETTINGS − FAN CIRCULATE (Page 11). When FAN − AUTO is
selected in the OPTIONS screen, the schedule is followed.
Controlling the Schedule
If backlight is not on continuous, press the screen
anywhere to turn on the backlight.
From the HOME screen press SCHED; repeated
presses toggle the schedule ON and OFF. If ON, the
system follows the program developed by the user
(Page 8).
If OFF, the system operates as a non−programmable thermostatthe
user must make changes when desired. The autochangeover feature
continues to operate based on the manual user inputs.
The fan mode is displayed on the SCHEDULE screen when program-
ming the thermostat and can be changed only during schedule editing
(after EDIT is pressed). Fan settings in OPTIONS screen will OVER-
RIDE the scheduled fan operation.

506228−01 05/09 Page 8
Schedule tabProgramming
If backlight is not on continuous, press the screen anywhere to turn on
the backlight. Press the SCHEDULE tab along the top of the screen.
The display changes to programming mode (figure 4) and shows the
current settings.
EVENTS DAILY 2 OR 4The thermostat may be programmed for two
or four (default) events per day. The names for the events are: WAKE,
LEAVE, RETURN, and SLEEP. The selected time for an event to occur
is based on when you want the event to begin. Four events (default) are
common for working households. To change to two events per day, see
page 11. When set for two events per day, the display would appear as:
WAKE (or SLEEP) PERIOD BEGINS".
WAKE PERIOD BEGINS
5:OOAM
Figure 4. Schedule Screen
Programmingmay be performed in groups of days or individual days,
as follows:
AMON TO SUN − allows every day to be set the same.
BMON TO FRI (weekday programming) and
SAT TO SUN (weekend programming).
CMONDAY through SUNDAY allows individual days of the week to be
programmed separately.
NOTE − After using one of the groups of days described above, the
program allows you to subsequently change individual days to suit your
needs.
To get to the different groupings of days, press EDIT, then press NEXT
repeatedly to scroll to the desired grouping.
Programming Complexity
The programming process for groups of days or individual days is the
same, except in the amount of times required to go through the process.
Full WeekThe least complex program is the full week MON TO
SUN" program, wherein the events for every day of the week are the
same. This requires one time through the event programming process.
Work WeekNext in complexity to the full week program is the work
week program wherein the events are set for a typical work week (MON
TO FRI) and different events are set for the weekend (SAT TO SUN).
This requires two times through the events.
Day by DayMost complex because this requires going through the
programming process 7 times.

Page 9 ComfortSensetModel L7742U Touch Screen 7−Day Programmable Thermostat
Schedule tabProgramming (continued)
Days & Events Programming process
Action Display shows...
1 Press SCHEDULE tab SCHEDULE screen
2 Press EDIT UP/DOWN arrows on right−hand
side of screen; EDIT changes to
CANCEL
3 Press NEXT to highlight the de-
sired grouping of days
Days change to match selected
group, e.g. MON TUE WED THU FRI
4 Press an event: WAKE (default),
LEAVE, RETURN, & SLEEP to
select for programming
Filled triangle above event
indicates which event is selected
for change
5 Press UP/DOWN arrows to
select desired temperature
After change is made, SAVE
appears in the bottom right−hand
of the screen
6 Press FAN repeatedly to select
desired fan mode
Fan indicator displays selection
(ON, AUTO, or CIRC)
7 Press UP/DOWN arrows to
adjust start time for
selected event
Information area displays start
time
8 Repeat steps 4 − 7 for all remaining events.
(If you selected other than MON TUE WED THU FRI SAT SUN), continue;
otherwise, skip to step 11.
9 Press NEXT for the next group
or the next day
Days change to match selected
group, e.g. SAT SUN
10 Repeat steps 3 through 8 for the remaining days, if necessary.
11 Press SAVE when all events and
days are programmed as desired
The changes are made and the
schedule screen reappears.
24
6
1
7
5
WAKE PERIOD BEGINS
5:OOAM
911
3
Figure 5. Programming days and events

506228−01 05/09 Page 10
Options tabReminders/User Settings
CLEAN button [OPTIONS TAB > [CLEAN] ]
When you select the OPTIONS tab, two buttons appear near the bot-
tom of the screen labeled CLEAN and ENTER. Press the CLEAN but-
ton to deactivate the touch" zones for 30 seconds. Clean the screen
with a soft cloth and a mild glass cleaning solution.
The Options screen provides user and installer access to the various
features for setup and access to the reminders.
REMINDERS
USER SETTINGS
Reminders [OPTIONS TAB > REMINDERS > [ENTER] ]
Set timers from 1 to 24 months in either calendar time or system run
time. Reminders appear when it is time to service the following (for
more details on REMINDERS, see Page 33):
REPLACE MEDIA FILTER
DUE FRI JUN 12 O9
REPLACE UV LAMP
DUE FRI SEP 11 O9
ROUTINE SYS CHECK−UP
DUE IN 216O HOURS
PURE AIR MAINTENANCE
DUE FRI SEP 11 O9
REPLACE HUM PAD
DUE FRI JUN 12 O9
(CUSTOM REMINDER 1)
DUE WED OCT 21 09
User Settings [OPTIONS TAB > USER SETTINGS > [ENTER] ]
12 OR 24 HOUR Page 10
BACKLIGHT INTENSITY Page 12
BACKLIGHT SETTING Page 12
COOLING LIMIT Page 12
DATE/TIME Page 10
DISPLAY INFO Page 11
EVENTS DAILY 2 OR 4 Page 11
F/C Page 10
FAN CIRCULATE Page 11
HEATING LIMIT Page 12
HUMIDITROL ADJUST Page 12
HUMIDITY SETTING Pages 12, 20, 22
SECURITY LOCK Page 12
VIEW CONTACT INFO Page 11
Press the OPTIONS tab; use the arrows to select USER SETTINGS.
Press ENTER.
USER SETTINGS
INSTALLER SETTINGS
The following items are available for modifying. Follow the instructions
for each parameter.
DATE/TIMESet month, day, year, hour, and minute using DATE/
TIME option. Select DATE/TIME; press ENTER. Small, filled up-arrow
is the selected column; use up/down arrows to adjust; press box below
each small up-arrow to select each column. Adjust; press SAVE.
FEB 11 2OO9 12PM 49
MON DAY YR HR MIN
CANCEL||||||SAVE|
F/Cdefault is Fahrenheit; to change to Celsius, scroll to F/C; press
ENTER. Use arrows to change to C; press SAVE.
F OR C
DEFAULT(F) F
12 OR 24 HOUR clockdefault is 12H; to change, scroll to 12 OR 24
HOUR; press ENTER. Use arrows to change to 24H; press SAVE.
12 OR 24 HOUR
DEFAULT(12HR) 12H