Lennox International Inc 51M32 Backup Heat Source Selection, 51M33 Terminal Designations

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Default Thermostat Settings

Default Thermostat settings are in table 1.

Table 1

Default Thermostat Settings

Mode

Heat

 

 

Setpoint

70°F (or 21°C)

 

 

Fan

Auto

 

 

Filter Reminder

OFF (reminder setting = 0)

 

 

Equipment Protection

reset back to zero

Timers

 

 

 

Technical Specifications

Thermostat Type

Electronic nonprogrammable thermostat for 1H/1C, heat pump with electric or gas backup heat source, non−power robbing applications.

Power Supply Range

18VAC − 30VAC (24VAC nominal), 60Hz

Temperature Display

Display Scale: Fahrenheit or Celsius user selectable (via DIP switches)

Display range: 35°F (2°C) to 99°F (37°C)

Display resolution: 1°F (1°C)

Display Accuracy: +/−1°F

Temperature Measurement Range

Measurement Scale: Fahrenheit

Measurement Range: 35°F to 99°F

Measurement Resolution: 0.5°F

Measurement Accuracy: +/−1°F

Field Offset: via DIP switches to +/−3°F

Sampling Method: temperature measurements sampled every 15 seconds. Displayed temperature is the average of the last four measurements.

Temperature Setpoint Range

Setting range: 50°F (10°C) to 90°F (32°C)

Setting resolution: 1°F (1°C)

Fan Control

AUTO or ON modes.

Backup Heat Source Selection

Electric or gas furnace, selectable via DIP switch #5 (Aux or Dual, respectively). See also Thermostat Output section.

I/O Relays

All thermostat relays are latching type to minimize power consumption. See table 2.

 

Table 2

51M33 Terminal Designations

 

 

Connections

Description

 

 

O

Reversing valve, cool active

 

 

B

Reversing valve, heat active

 

 

R

24VAC

 

 

G

Fan control

 

 

Y1

First stage cooling/heating, compres-

 

sor generated

 

 

W1

Auxiliary heating, furnace generated

 

 

L

Service Indicator

 

 

C

24VAC common

 

 

E

Emergency heat

 

 

T

Outdoor temperature sensor

 

connection 1

 

 

T

Outdoor temperature sensor

 

connection 2

 

 

Equipment Protection Timers

Minimum Compressor OFF time: 5 minutes

Minimum Compressor ON time: 4 minutes

Minimum Furnace ON time: 3 minutes

Minimum backup furnace cycle time (elapsed time be- tween any furnace activation and the next furnace activa- tion): 6 minutes.

Minimum elapsed time between any compressor activation and the next compressor activation: 6 minutes.

NOTE − All protection timers (except the compressor OFF timer) can be over−ridden if a heating or cooling demand is initiated or terminated using the UP, DOWN, HEAT, or COOL buttons.

Equipment Protection Override

Both the minimum compressor OFF timer and the mini- mum equipment cycle timer can be over−ridden by press- ing and holding either the HEAT or COOL button down for 4 seconds.

Over−Temperature Protection

Thermal mechanical switch opens W1 at 93°F+/−6°F.

Filter Reminder

Settings of 0 (Off), 1, 3, 6 or 12 months are available. When programmed time has elapsed, a FILTER indicator is dis- played.

Balance Point

0°F (OFF) to 55°F, user selectable.

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Contents Table of Contents Initial Thermostat Power-upMeritR Series Thermostat GeneralHeat Mode Enabled Heat Mode DisabledHeating Control Display − Home ScreenAdjusting Temperature Setpoint Enabling and Disabling Cool ModeSetpoint Display and Adjustment Cooling ControlFan Control Filter ReminderService Indicator Thermostat ResetDefault Thermostat Settings Technical SpecificationsThermostat Output Table Controls 51M33 Additional Thermostat Buttons Normal Heat Mode Emergency Heat ModeNormal Heat Mode Enabled Emergency Heat Mode EnabledCooling Control Fan Control Balance Point Setting Service Indicator Flashing RoomBalance Point Backup Heat Source Selection 51M33 Terminal DesignationsBalance Point Thermostat Output Table Electric Heat Backup − No Outdoor Sensor Gas Heat Backup Dual Fuel − No Outdoor SensorElectric Heat Backup − Outdoor Sensor Attached Gas Heat Backup Dual Fuel − Outdoor Sensor Attached