Filter
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05/05 505,049M
*2P0505* *P505049M*
Page 1
E2005 Lennox Industries Inc.
Dallas, Texas, USA
RETAIN THESE INSTRUCTIONS
FOR FUTURE REFERENCE
51M35 Merit
®
Series Thermostat
The Lennox Merit
®
Series 5/2 day programmable
electronic thermostat 51M35 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 51M35 is suitable for non-heat pump, two-
stage heat/two-stage cool applications using a gas or elec-
tric furnace.
OPERATION
MANUAL
51M35 Merit
®
Series
5/2 Day Programmable Thermostat
CONTROLS
505,049M
05/05
Supersedes 03/05
Table of Contents
51M35 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. . . . . . . . . . . . . . . . . . . . . . . . . . . .
HOLD − Temperature Hold Mode 4. . . . . . . . . . . . . . . .
PROG − Thermostat Programming 4. . . . . . . . . . . . . . .
FAN − Controlling Fan Operation 5. . . . . . . . . . . . . . . . .
SETTINGS − Filter /Maintenance Reminder 5. . . . . . .
Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removing/Installing Thermostat 6. . . . . . . . . . . . . . . . .
Default Thermostat Settings 6. . . . . . . . . . . . . . . . . . . .
Technical Specifications 7. . . . . . . . . . . . . . . . . . . . . . . .
Thermostat Output Table 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 thermostat
51M35. Refer to the installation manual for instructions re-
garding 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.
FAN
ON
AUTO
SYSTEM
COOL
OFF
EMG.
HEAT
I8:88
88
Figure 1
AM
PM
ROOM
88
MO TU WE TH FR SA SU
SETPOINT
°
°
Initial Power−Up Display
SERVICE
FILTER
MAINT
Hi
Lo
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.