Filter
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07/05 505,068M
*2P0705* *P505068M*
Page 1
E2005 Lennox Industries Inc.
Dallas, Texas, USA
RETAIN THESE INSTRUCTIONS
FOR FUTURE REFERENCE
51M39 Merit
®
Series Thermostat
The Lennox Merit
®
Series 7 day programmable electronic
thermostat 51M39 provides excellent temperature control
and 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 51M39 is suitable for non-heat pump, two-
stage heat/two-stage cool applications using a gas or elec-
tric furnace. Also, the thermostat provides autochange-
over capability.
OPERATION
MANUAL
51M39 Merit
®
Series
7 Day Programmable Thermostat
CONTROLS
505,068M
07/05
Table of Contents
51M39 Series Thermostat 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 4. . . . . . . . .
HOLD − Temperature Hold Mode 4. . . . . . . . . . . . . . . .
PROG − Thermostat Programming 4. . . . . . . . . . . . . . .
COPY − Copy a Program 6. . . . . . . . . . . . . . . . . . . . . . .
FAN − Controlling Fan Operation 5. . . . . . . . . . . . . . . . .
Displaying Outside Temperature 6. . . . . . . . . . . . . . . . .
SETTINGS − Filter /Maintenance Reminder 6. . . . . . .
Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removing/Installing Thermostat 7. . . . . . . . . . . . . . . . .
Default Thermostat Settings 7. . . . . . . . . . . . . . . . . . . .
Thermostat Output Table 7. . . . . . . . . . . . . . . . . . . . . . .
Technical Specifications 8. . . . . . . . . . . . . . . . . . . . . . . .
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 thermo-
stat 51M39. 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 dis-
play will appear as shown in figure 1.
HEAT SETPOINT
COOL
OFF
AUTO
EMG.
HEAT
I8:88
i88
Figure 1
AM
PM
OUTROOM
MO TU WE TH FR SA SU
COOL SETPOINT
Initial Power−Up Display
FILTER
MAINTENANCE
Hi
Lo
FAN ON
AUTO
°
°
°
SERVICE
Copy tofrom
PROG
A B C D
HOLD
All display segments are momentarily activated. This oc-
curs as a normal part of thermostat initialization.
Litho U.S.A.