Lennox International Inc 51M37 P505069M, 51M42 Merit Series Thermostat, Pm, 2P0705, General

E2005 Lennox Industries Inc.

Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS

FOR FUTURE REFERENCE

51M42 Merit® Series Thermostat

The Lennox Merit® Series 7−day programmable electronic thermostat 51M42 provides excellent temperature control and a large, easy-to-read display. It 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 51M42 is suitable for heat pump, three-stage heat/two-stage cool applications using a gas or electric auxiliary heat source. In addition to displaying outdoor temperature, the outdoor temperature sensor provides auxiliary heat lockout, balance point operation, and dual− fuel compatibility. Also, the thermostat provides auto- changeover capability.

OPERATION

MANUAL

51M42 Merit® Series

7−Day Programmable Thermostat

CONTROLS

505,069M
	Litho U.S.A.
07/05

Table of Contents

51M42 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

AUTO − Using the Autochangeover Mode . . . . . . . . . 4

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

PROG − Thermostat Programming . . . . . . . . . . . . . . . 5

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

FAN − Controlling Fan Operation . . . . . . . . . . . . . . . . . 6

Displaying Outside Temperature . . . . . . . . . . . . . . . . . 6

SETTINGS − Filter and Maintenance Reminders . . . 6

SETTINGS − Balance Point . . . . . . . . . . . . . . . . . . . . . 7

Service Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Thermostat RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Removing/Installing Thermostat . . . . . . . . . . . . . . . . . 7

Default Thermostat Settings . . . . . . . . . . . . . . . . . . . . 7

Technical Specifications . . . . . . . . . . . . . . . . . . . . . . . . 9

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 51M42. 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.

Initial Power−Up Display

Copy tofrom MO TU WE TH FR SA SU
PROG	AM
A B C D
HOLD	PM I8:88
FAN ON	COOL SETPOINT
AUTO
		°
FILTER SERVICE			COOL
MAINTENANCE
			OFF
OUTROOM			AUTO
		HEAT SETPOINT	EMG.
	°
		°	HEAT
i88			Hi
			Lo

Figure 1

All display segments are momentarily activated. This oc- curs as a normal part of thermostat initialization.

07/05	Page 1	505,069M
*2P0705*		*P505069M*