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Lennox 51M37 - page 1
05/05 505,050M *2P0505* *P505050M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M37 Merit ® Series Thermost at The Lennox Merit ® Series 5/2 day programmable electronic thermostat 51M37 provides excellent temperature control and a large, easy-to-read display . It includes a programmabl ...
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Lennox 51M37 - page 2
Page 2 505050M 5/1/05 Within a few seconds, the Home Screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. NOTE − T ables 2 and 3 on page 8 show all system and programming default s. I2:00 PROG A B C D HOLD FA N ON AUTO SYSTEM COOL OFF HEA T 70 H ...
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Lennox 51M37 - page 3
Page 3 51M37 SERIES 5/2 HEA T − Using the Heat Mode Normal Heat Mode In normal heat mode, both the heat pump and the backup heat source are used to provide heat. If the thermost at d e- tects that the heat pump is not able to provide enough heat (as may be the case in very cold weather), then the backup heat source is activated. Emergency Heat Mo ...
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Lennox 51M37 - page 4
Page 4 505050M 5/1/05 COOL − Using the Cool Mode Enabling and Disabling Cool Mode Use the COOL button to enable or disable cool mode as desired. If the thermostat is in HEA T or OFF mode, cool mo d e is enabled when the COOL button is pressed. This is indicated by COOL in the SYSTEM box (s ee f i gu r e 9). T urn Cool ON/OFF Figure 9 I0:30 75 70 ...
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Lennox 51M37 - page 5
Page 5 51M37 SERIES 5/2 HOLD − Using T emperature Hold Modes When HOLD is displayed at the HOME screen, the ther- mos tat is in a temperature hold condition. This means that the temperature program data is ignored and the thermo- stat functions much like a non−programmable thermost at. Adjusting T emperature Setpoint in Hold Mode The temperatur ...
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Lennox 51M37 - page 6
Page 6 505050M 5/1/05 5. Repeat step s 2 through 4 for periods B, C, and D. 6. Repeat step s 1 through 5 for the 2−day program. NOTE − This thermost at will NOT automatically switch from heating to cooling, or vice versa; operator involve- men t is required. At the change of seasons, or to accomo- date abnormal seasonal temperature swings, you ...
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Lennox 51M37 - page 7
Page 7 51M37 SERIES 5/2 SETTINGS − Balance Point NOTE − The balance point is only available with the out- door sensor . If the optional outdoor sensor (X2658) is connected to the thermostat, balance point adjustment is available. The bal- ance point feature allows the measured outdoor tempera- ture to govern operation of the heat pump and backu ...
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Lennox 51M37 - page 8
Page 8 505050M 5/1/05 Default Thermostat Settings Default thermostat settings are shown in table 2 and the default program is shown in table 3. T able 2 Default Thermostat Settings Mode Heat (Permanent Hold Mode) Setpoint 70°F (or 21°C) Fan Auto Filter Reminder OFF Maintenance Reminder OFF Equipment Protection T imers Reset Back to Zero T able 3 ...
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Lennox 51M37 - page 9
Page 9 51M37 SERIES 5/2 Smart Setback Recovery (via DIP switch #6) Smart Setback Recovery (SSR) affects the way the ther- mo st at responds to program events. If SSR is disabled, th e thermostat will react to a program event at the time the event occurs. However , if SSR is enabled, the thermostat will react to a program event before the event occu ...
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Lennox 51M37 - page 10
Page 10 505050M 5/1/05 Thermostat Output T able T able 5 depicts the 51M37 thermostat output st ates for var- ious input conditions. The following notes described terms used in the t able. NOTES: S X = output is activated with 24V AC. S BBP: outdoor temperature is below balance point S ABP: outdoor temperature is above balance point S In all cases, ...
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Lennox 51M37 - page 11
05/05 505,049M *2P0505* *P505049M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M35 Merit ® Series Thermost at 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 p ...
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Lennox 51M37 - page 12
Page 2 505049M 5/1/05 Within a few seconds, the Home Screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. NOTE − T ables 2 and 3 on page 6 show all system and programming default s. I2:00 PROG A B C D HOLD FA N ON AUTO SYSTEM COOL OFF HEA T 70 H ...
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Lennox 51M37 - page 13
Page 3 51M35 SERIES 5/2 HEA T − Using the Heat Mode Enabling and Disabling Heat Mode The thermostat must be in the HEA T mode to control the heating equipment. Press the Heat button to enable or dis- able HEA T mode. If the thermostat is in COOL or OFF mode, pressing the Heat button enables the HEA T mode (indicated by HEA T in the S YS TE M b o ...
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Lennox 51M37 - page 14
Page 4 505049M 5/1/05 HOLD − Using T emperature Hold Modes When HOLD is displayed at the HOME screen, the ther- mos tat is in a temperature hold condition. This means that the temperature program data is ignored and the thermo- stat functions much like a non−programmable thermost at. Adjusting T emperature Setpoint in Hold Mode The temperature ...
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Lennox 51M37 - page 15
Page 5 51M35 SERIES 5/2 NOTE − This thermost at will NOT automatically switch from heating to cooling, or vice versa; operator involve- men t is required. At the change of seasons, or to accomo- date abnormal seasonal temperature swings, you must manually select to the opposite conditioning (Heat or Cool) program. F AN − Controlling the Fan Ope ...
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Lennox 51M37 - page 16
Page 6 505049M 5/1/05 Service Indicator When abnormal equipment operation is detected, the SERVICE in d icator will flash on the screen (see figure 17). This indicates that the equipment requires service from a qualified service technician. I0:i4 PROG A B C D HOLD 79 Service Indicator Flashing Figure 17 ROOM SER VICE ° FIL TER AM PM FA N ON AUTO S ...
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Lennox 51M37 - page 17
Page 7 51M35 SERIES 5/2 T echnical S pecifications Thermostat T ype Electronic programmable thermostat for 2−S tage (gas or electric) Heat/2-S tage Cool, non−heat pump, non−power robbing applications. Power Supply Range 18V AC − 30V AC (24V AC nominal), 60Hz CAUTION 24V AC is present on the terminals of the thermost at bracket. If removing ...
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Lennox 51M37 - page 18
Page 8 505049M 5/1/05 Maintenance Reminder Settings of Of f, 6 or 12 (months of chronological time) are available. W hen programmed time has elap sed, a mainte- nance indicator MAINT" is displayed. Service Reminder The SER VICE indicator is displayed only under the follow- ing conditions: S if the thermostat Y1 terminal has been activated w ...
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Lennox 51M37 - page 19
05/05 505,048M *2P0505* *P505048M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M34 Merit ® Series Thermost at The Lennox Merit ® Series 5/2 day programmable electronic thermostat 51M34 provides excellent temperature control and a large, easy-to-read display . This product includes a p ...
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Lennox 51M37 - page 20
Page 2 505048M 5/1/05 Within a few seconds, the Home Screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. I2:00 PROG A B C D HOLD FA N ON AUTO SYSTEM COOL OFF HEA T 70 Home Screen Figure 2 ROOM SER VICE ° FIL TER MAINT MO TU WE TH FR SA SU AM PM ...
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Lennox 51M37 - page 21
Page 3 51M34 SERIES 5/2 HEA T − Using the Heat Mode Enabling and Disabling Heat Mode The thermostat must be in the HEA T mode to control the heating equipment. Press the Heat button to enable or dis- able HEA T mode. If the thermostat is in COOL or OFF mode, pressing the Heat button enables the HEA T mode (indicated by HEA T in the S YS TE M b o ...
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Lennox 51M37 - page 22
Page 4 505048M 5/1/05 HOLD − Using T emperature Hold Modes When HOLD is displayed at the HOME screen, the ther- mos tat is in a temperature hold condition. This means that the temperature program data is ignored and the thermo- stat functions much like a non−programmable thermost at. Adjusting T emperature Setpoint in Hold Mode The temperature ...
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Lennox 51M37 - page 23
Page 5 51M34 SERIES 5/2 NOTE − This thermost at will NOT automatically switch from heating to cooling, or vice versa; operator involve- men t is required. At the change of seasons, or to accomo- date abnormal seasonal temperature swings, you must manually select to the opposite conditioning (Heat or Cool) program. F AN − Controlling the Fan Ope ...
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Lennox 51M37 - page 24
Page 6 505048M 5/1/05 Service Indicator When abnormal equipment operation is detected, the SERVICE in d icator will flash on the screen (see figure 17). This indicates that the equipment requires service from a qualified service technician. I0:i4 PROG A B C D HOLD 79 Service Indicator Flashing Figure 17 ROOM SER VICE ° FIL TER AM PM FA N ON AUTO S ...
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Lennox 51M37 - page 25
Page 7 51M34 SERIES 5/2 T echnical S pecifications Thermostat T ype Electronic programmable thermostat for 1-S tage- Heat/1-S tage Cool, gas or electric heat, non−heat pump, non−power robbing applications. Power Supply Range 18V AC − 30V AC (24V AC nominal), 60Hz CAUTION 24V AC is present on the terminals of the thermost at bracket. If removi ...
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Lennox 51M37 - page 26
Page 8 505048M 5/1/05 Maintenance Reminder Settings of Of f, 6 or 12 (months of chronological time) are available. W hen programmed time has elap sed, a mainte- nance indicator MAINT" is displayed. Service Reminder The SER VICE indicator is displayed only under the follow- ing conditions: S if the thermostat Y1 terminal has been activated w ...
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Lennox 51M37 - page 27
07/05 505,068M *2P0705* *P505068M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M39 Merit ® Series Thermost at 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 pro ...
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Lennox 51M37 - page 28
Page 2 505068M 07/05 Within a few seconds, the HOME screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. NOTE − T ables 2 and 3 on page 7 show all system and programming default s. COOL OFF AUTO EMG. HEAT I0:26 PROG A B C D HOLD F AN ON AUT O 70 ...
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Lennox 51M37 - page 29
Page 3 51M39 SERIES 5/2 HEA T − Using the Heat Mode Enabling and Disabling Heat Mode The thermostat must be in the heat mode to control the heating equipment. Press the HEA T button to enable or disable HEA T mode. If the thermost at is in cool or of f mode, pressing the HEA T button enables the heat mode (indicated by HEA T in the lower right co ...
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Lennox 51M37 - page 30
Page 4 505068M 07/05 NOTE − If no buttons are pressed during a demand for cooling, t he equipment must operate for at least 4 minutes. Afte r a demand has been satisfied, cooling equipment op- eration is locked out for 5 minutes. If another cooling de- ma nd occurs during this 5−minute interval, COOL" and the snowflakes will flash; howe ...
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Lennox 51M37 - page 31
Page 5 51M39 SERIES 5/2 Figure 1 1 Program Example 6AM NOON 6PM MID 6AM NIGHT A B D A B D A B D A B D A B C D A B C D A B C D C C C C SA TURDA Y PROGRAM: 72° 68° 64° SUNDA Y PROGRAM: 72° 68° 64° FRIDA Y PROGRAM: 72° 68° 64° THURSDA Y PROGRAM: 72° 68° 64° WEDNESDAY PROGRAM: 72° 68° 64° TUESDA Y PROGRAM: 72° 68° 64° MONDA Y PROGRAM: ...
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Lennox 51M37 - page 32
Page 6 505068M 07/05 Displaying Outside T emperature Pressing the ENTER (Outside) button at the HOME screen di sp l ays the out side temperature (see figure 15) for several seconds, then returns to room temperature. Check Outside T emperature Figure 15 88 Fan Settings Hold Enter (Outside) SETTINGS − Filter/Maintenance Reminders Th e 51M39 thermos ...
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Lennox 51M37 - page 33
Page 7 51M39 SERIES 5/2 Removing and Installing Thermostat The thermostat hinges on tabs on the top of the subbase; no tool is needed to remove the thermostat from the sub- base. Pivot the bottom of the thermostat outward (releas- ing the snap s), then lif t up to remove. T o install it, first position the top tilted toward the wall brack- et and a ...
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Lennox 51M37 - page 34
Page 8 505068M 07/05 T echnical S pecifications Thermostat T ype Electronic programmable thermostat for 2−S tage (gas or electric) Heat/2-S tage Cool, non−heat pump, non−power robbing applications. T able 5 51M39 T erminal Designations T erminal Description R 24V AC Y1 First-stage cooling W1 First-stage heating Y2 Second-stage cooling W2 Seco ...
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Lennox 51M37 - page 35
Page 9 51M39 SERIES 5/2 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, HEA T , or COOL buttons. Equipment Protection Override Both the minimum compressor OFF timer and the mini- mum equipment cycle timer can be over−ridden by pres ...
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Lennox 51M37 - page 36
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Lennox 51M37 - page 37
07/05 505,069M *2P0705* *P505069M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M42 Merit ® Series Thermost at The Lennox Merit ® Series 7−day programmable electronic thermostat 51M42 provides excellent temperature control and a large, easy-to-read display . It includes a programmabl ...
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Lennox 51M37 - page 38
Page 2 505069M 07/05 Within a few seconds, the HOME screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. NOTE − T ables 2 and 3 on page 8 show all system and programming default s. COOL OFF AUTO EMG. HEAT I0:26 PROG A B C D HOLD F AN ON AUT O 70 ...
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Lennox 51M37 - page 39
Page 3 51M42 SERIES 5/2 HEA T − Using the Heat Mode Normal Heat Mode In normal heat mode, both the heat pump and the backup heat source are used to provide heat. If the thermost at d e- tects that the heat pump is not able to provide enough heat (as may be the case in very cold weather), then the backup heat source is activated. Emergency Heat Mo ...
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Lennox 51M37 - page 40
Page 4 505069M 07/05 COOL − Using the Cool Mode Enabling and Disabling Cool Mode Use the COOL button to enable or disable cool mode as desired. If the thermosta t i s in heat or of f mode, cool mode is enabled when the COOL button is pressed. This is indi- cated by COOL on the r igh t si de of the disp lay (s e e fig u r e 9). Heat Prog Fan Setti ...
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Lennox 51M37 - page 41
Page 5 51M42 SERIES 5/2 T emporary (2-Hour) Hold At any time the program is running, from the HOME screen, set a temporary 2-hour hold by pressing the Up/ Down arrow buttons until the desired setpoint is displayed; HOLD" flashes (see figure 12). This overrides the pro- gram for 2 hours from the last button press, then returns to the program ...
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Lennox 51M37 - page 42
Page 6 505069M 07/05 F AN − Controlling the Fan Operation U s e the F AN button to select either continuous fan mode or auto fan mode. T o change from continuous to auto fan mode (or vice ver - sa), press the F AN button. Note whether a fan icon in the F AN b ox is present (indicating that the fan is running) or not (fan not running) . If continu ...
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Lennox 51M37 - page 43
Page 7 51M42 SERIES 5/2 COOL OFF AUTO EMG. HEAT I0:26 PROG A B C D HOLD F AN ON AUT O FIL TER S ER VICE MAINTENANCE 76 Reminders Figure 19 ROOM ° MO AM PM COOL OFF AUTO EMG. HEAT FA N ON AUT O FIL TER S ER VICE MAINTENANCE 76 Service Indicator Flashing ROOM ° Filter & Maintenance Indicators After the filter has been changed or maintenance per ...
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Lennox 51M37 - page 44
Page 8 505069M 07/05 Default Thermostat Settings Default thermostat settings are shown in table 2 and the default program is shown in table 3. T able 2 Default Thermostat Settings Mode Heat (Perm. Hold) Heat Setpoint (Perm Hold) 70°F (or 21°C) Cool Setpoint (Perm Hold) 78°F (or 26°C) Fan Auto Filter Reminder OFF Maintenance Reminder OFF Equipme ...
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Lennox 51M37 - page 45
Page 9 51M42 SERIES 5/2 T echnical S pecifications Thermostat T ype Electronic programmable thermostat for heat pump, 3-stage heat/2-st age cool. NOTE − 2 s t ages of heat pump heat and one st age of auxil- iary (gas or electric) backup heat are supported. Power Supply Range 18V AC − 30V AC (24V AC nominal), 60Hz CAUTION 24V AC is present on th ...
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Lennox 51M37 - page 46
Page 10 505069M 07/05 T able 5 51M42 T erminal Designations T erm. Description B Reversing valve, heat active O Reversing valve, cool active R 24V AC Y1 First-stage cooling/heating, compressor energized W1* Auxiliary heating, furnace energized Y2 Second-stage cooling/heating, compressor energized E* Emergency heat G Fan control L Service Indicator ...
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Lennox 51M37 - page 47
07/05 505,067M *2P0705* *P505067M* Page 1 E 2005 Lennox Industries Inc. Dallas, T exas, USA RET AIN THESE INSTRUCTIONS FOR FUTURE REFERENCE 51M38 Merit ® Series Thermost at The Lennox Merit ® Series 7 day programmable electronic thermostat 51M38 provides excellent temperature control and a large, easy-to-read display . This product includes a pro ...
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Lennox 51M37 - page 48
Page 2 505067M 7/13/05 Within a few seconds, the HOME screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed. COOL OFF AUTO EMG. HEAT I0:26 PROG A B C D HOLD F AN ON AUT O 70 HOME Screen Figure 2 ROOM ° MO AM PM At this point, the thermostat will be ...
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Lennox 51M37 - page 49
Page 3 51M38 SERIES 5/2 HEA T − Using the Heat Mode Enabling and Disabling Heat Mode The thermostat must be in the heat mode to control the heating equipment. Press the HEA T button to enable or disable heat mode. If the thermost at is in cool or of f mode, pressing the HEA T button enables the heat mode ( i n d i- cated by HEA T in the lower rig ...
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Lennox 51M37 - page 50
Page 4 505067M 7/13/05 HOLD − Using T emperature Hold Modes When HOLD is displayed at the HOME screen, the ther- mos tat is in a temperature hold condition. This means that the temperature program data is ignored and the thermo- stat functions much like a non−programmable thermost at. Adjusting T emperature Setpoint in Hold Mode The temperature ...
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Lennox 51M37 - page 51
Page 5 51M38 SERIES 5/2 1. Press and re lease the PROG button. "MO" (Monday), "AM 6:00", period "A", "COOL SETPOINT 78", and "HEA T SETPOINT 70" are displayed. "AM 6" flashes. 2. Use the Up/Down arrow buttons to select the desired hour; press the PROG button when the desired hour is reache ...
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Lennox 51M37 - page 52
Page 6 505067M 7/13/05 The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals. T able 1 Filter and Maintenance Reminders Buttons to Use Reminder A vailable Settings and How to Use SETTINGS (1st press) FIL TER T otal fan run time expressed in months (Of f136 12); for (1 s t pre ...
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Lennox 51M37 - page 53
Page 7 51M38 SERIES 5/2 T able 3 Default Program Settings (Time & T emp.) Programs Time T emp. − Heat T emp. Cool All days − A 6:00am 70 _ F / 21 ° C 78 _ F / 26 ° C All days − B 8:00am 62 _ F / 17 ° C 85 _ F / 29 ° C All days − C 6:00pm 70 _ F / 21 ° C 78 _ F / 26 ° C All days − D 10:00pm 62 _ F / 17 ° C 82 _ F / 28 ° C Therm ...
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Lennox 51M37 - page 54
Page 8 505067M 7/13/05 Smart Setback Recovery (via DIP switch #6) Smart Setback Recovery (SSR) affects the way the ther- mo st at responds to program events. If SSR is disabled, th e thermostat will react to a program event at the time the event occurs. However , if SSR is enabled, the thermostat will react to a program event before the event occur ...
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