Lennox L3722C Programmable Thermostat
The Lennox ComfortSense 3000 Series model L3722C 7-day programmable electronic thermostat provides excellent temperature control and has 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 model L3722C is suitable for non-heat pump, two-stage heat/two-stage cool applications using a gas or electric furnace. Also, the thermostat provides the auto-changeover capability.
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 the Lennox model L3722C thermostat. Refer to the installation manual for instructions regarding the installation and wiring of the thermostat.
Initial Thermostat Power-up When power is initially applied to the thermostat, the display will appear as shown in figure 1.
All display segments are momentarily activated. This occurs as a normal part of thermostat initialization. Within a few seconds, the HOME screen appears (see figure 2 with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed.
NOTE − Tables 3 and 4 on page 7 show all system and programming defaults.
At this point, the thermostat will be fully functional; its default temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.
NOTE − The temperature scale default is Fahrenheit units but may be reset to show Celsius if desired. See page 8. Buttons, Backlight, Timers & Settings Buttons are located behind the small door on the right-hand side of the thermostat (see figure 3).
IMPORTANT
Do NOT begin pressing buttons until after you read the following section describing each button. A pale blue display backlight illuminates for 30 seconds each time any button is pressed.
When the PROG or DAY/TIME button is pressed, a field begins flashing, expecting another input. Start making changes within 15 seconds or the HOME screen will return.
When an Arrow, HOLD, HEAT, or COOL button is pressed, SETPOINT and the temperature setting appear for 15 seconds. If desired, start making changes within 15 seconds or the HOME screen will return. The backlight will turn off 15 seconds after the HOME screen reappears.
DAY/TIME − Setting the Day and Time
Press the DAY/TIME button and set the CURRENT hour, minute, and day of the week as follows:
- AM12″ will flash on the screen. Press the UP/DOWN arrows to change the hour. (AM” or PM” must correspond to the time of day.) Press DAY/TIME OR, if adjusting for daylight savings time, pressing the ENTER button stores the single change and exits to the HOME screen, bypassing minutes and day of the week.
- Minutes will flash. Use the UP/DOWN arrow button to display the minutes past the hour. Press DAY/TIME.
- Day MO” (Monday) will flash. Use the UP or DOWN arrow buttons to display the current day. Day selections are abbreviated as MO, TU”, WE”, TH”, FR”, SA”, SU”. Press DAY/TIME.
- The HOME screen reappears; confirm day and time are correct. This completes the day and time setting.
HEAT − Using the Heat Mode
Enabling and Disabling Heat Mode The thermostat must be in heat mode to control the heating equipment. Press the HEAT button to enable or disable HEAT mode. If the thermostat is in cool or off mode, pressing the HEAT button enables the heat mode (indicated by HEAT in the lower right corner − see figure 4).
If the thermostat is in heat mode, heat mode is disabled when the HEAT button is pressed. This is indicated by OFF near the right side of the display as shown in figure 5.
Heating Demand
Set the thermostat to heat mode to control the heating equipment. Then, if the room temperature is lower than the temperature setpoint, as shown in figure 6, the thermostat detects a heating demand and will activate the heating equipment to satisfy the demand.
The heating operation is indicated by a flame icon in the lower right corner. When the actual temperature rises above the temperature setpoint, the flame icon will disappear. This indicates that the heating demand has been satisfied and that the heating equipment has been turned off. If your system supports 2−stage heating (as does the L3722C thermostat), you may notice various heating levels being delivered during a demand. NOTE − Heating equipment is activated for at least 3 minutes if no buttons are pressed during the demand interval.
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 heat or off mode, the cool mode is enabled when the COOL button is pressed. This is indicated by COOL on the right side of the display (figure 8).
If the thermostat is in cool mode, press the COOL button disables cool mode (indicated by OFF in the SYSTEM box − see figure 5).
Cooling Demand
Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than the temperature setpoint, as shown in figure 7, the thermostat detects a cooling demand and will activate the cooling equipment to satisfy the demand. Cooling operation is indicated by flashing snowflake” icons on the right side of the display. When the actual temperature drops below the temperature setpoint, the snowflake icons will disappear. This indicates that the cooling demand has been satisfied and that the cooling equipment has been turned off. If your system supports 2−stage cooling (as does the L3722C thermostat), you may notice various cooling levels being delivered during a demand. Also, if a small cooling demand is present, “Lo” will be displayed in the SYSTEM box. However, if a large cooling demand is present, “Hi” will be displayed in the lower right corner (shown in figure 8)
NOTE − If no buttons are pressed during the demand for cooling, the equipment must operate for at least 4 minutes. After a demand has been satisfied, the cooling equipment operation is locked out for 5 minutes. If another cooling demand occurs during this 5−minute interval, COOL” and the snowflakes will flash; however, the cooling equipment will not operate until the 5−minute delay has elapsed.
AUTO − Using the Autochangeover Mode
When in either heat mode or cool mode, autochangeover can be enabled or disabled by pressing the AUTO button. If enabled, AUTO appears at the lower right corner of the display. The thermostat will then automatically change over from heating to cooling and vice versa, to keep the room temperature in between the heating and cooling setpoints. Autochangeover can be used in either of the thermostat hold modes or when the thermostat program is running. These modes are described later.
HOLD − Using Temperature Hold Modes
When HOLD is displayed at the HOME screen, the thermostat is in a temperature-hold condition. This means that the temperature program data is ignored and the thermostat functions much like a non−programmable thermostat. Adjusting Temperature Setpoint in Hold Mode The temperature setpoint represents the desired temperature of the space around the thermostat. The default heat setpoint in hold mode is 70°F; the default cool setpoint in hold mode is 78°F.
To adjust the setpoint, press the UP or DOWN arrow buttons; the existing setpoint is displayed to the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree After the desired setpoint is reached, the HOME screen will reappear after about 15 seconds.
Permanent Hold Mode
At any time the program is running, from the HOME screen, set a permanent hold (program override) by pressing the HOLD button (see figure 9). The thermostat now functions much like a non−programmable thermostat. Use the Up/Down arrow buttons to adjust the hold setpoint. To return to the program, press the HOLD button again.
Temporary (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 10). This overrides the program for 2 hours from the last button press, then returns to the program. While in Temporary Hold, press the HOLD button once to switch to Permanent Hold (HOLD displays solid; PROG not displayed); press the HOLD button again to return to the program (PROG displays; HOLD not displayed).
PROG − Thermostat Programming
The L3722C thermostat can be programmed to perform a set of both heating and cooling events for each day of the week. Each day can be programmed for 4 unique events per day, and each day can be different from any other day. To Set Program Events and Temperatures Figure 11 gives an example of how up to 7 different programs can be set. Programs A and C reflect the desired warmth while the home IS occupied (72°); B allows less heating while the home is NOT occupied; D reflects a cool sleeping temperature.
NOTE − This example shows heat setpoints; a similar program may be set for cool setpoints.
NOTE − Pressing the ENTER button during the following programming steps, saves and exits to the HOME screen. To program events and temperatures, perform the following
steps.
- Press and release the PROG button. “MO” (Monday), “AM 6:00”, period “A”, “COOL SETPOINT 78”, and “HEAT SETPOINT 70” is displayed. “AM 6” flashes.
- Use the Up/Down arrow buttons to select the desired hour; press the PROG button when the desired hour is reached; use the Up/Down arrow buttons again to select desired minute. The selected hour/minute is when the program will start. Press the PROG button.
- Use the Up/Down arrow buttons to select the desired heat setpoint; press the PROG button.
- Use the Up/Down arrow buttons to select the desired cool setpoint; press the PROG button.
- Repeat steps 1 − 4 for Monday, periods B, C, and D.
- COPY A PROGRAM − If the program entered for Monday is satisfactory for other days of the week, do the following to repeat the same program for other days:
Press the PROG button, then press the COPY button. The display clears the screen except for Copy from MO with MO” flashing. Press the COPY button again to copy Monday’s program.
The display changes to Copy to MO”. Use the arrow buttons to scroll to the desired day where you want the same program as Monday. Press the COPY button. C Repeat steps A and B for as many days as you want the same program.
Repeat steps 1 − 5 to program different times and temperatures for days not yet programmed.
FAN − Controlling the Fan Operation
Use the FAN button to select either continuous fan mode or auto fan mode. To change from continuous to auto fan mode (or vice versa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running). If continuous fan mode is enabled (ON displayed in FAN box − see figure 13), the fan will run continuously regardless of whether the heating or cooling equipment is running.
If auto fan mode is selected (AUTO displayed in FAN box − see figure 14), the fan will only run when the heating or cooling equipment is running.
Displaying Outside Temperature
Pressing the ENTER (Outside) button at the HOME the screen displays the outside temperature (see figure 15) for several seconds then returns to room temperature.
SETTINGS − Filter/Maintenance Reminders
The L3722C thermostat is designed to remind you when the filter needs changing or when routine maintenance is required, as (and if) defined, by you. These optional reminders are not enabled until you activate them. To do so, press the SETTINGS button once or twice for the desired reminder as shown in figure 16 and as described in table 1.
The default setting for the reminders is OFF (disabled). Press the Up/Down arrow buttons to select the desired reminder intervals.
Table 1. Filter and Maintenance Reminders
NOTE − The HOME screen will reappear about 15 seconds after the final arrow button is pressed. OR, press the ENTER button at any time to store any changes and exit to the HOME screen. After either programmed interval has elapsed, the reminder will be displayed as shown in figure 17.
After the filter has been changed or maintenance performed, reset the reminder by pressing the SETTINGS button for 4 seconds at the corresponding reminder settings screen. The screen will blink for a few moments to indicate that the timer has been reset.
Service Indicator
When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 17). This indicates that the equipment requires service from a qualified service technician.
Thermostat RESET
Under some abnormal conditions, it may be necessary to reset” the thermostat to its default condition. Such a RESET would delete all programming and settings and therefore should only be used on rare occasions when the thermostat fails to function as designed and/or as programmed. Such an instance can occur as a result of a power surge or similar electrical disturbance (e.g. after an electrical storm or power outage). The RESET button can be used to recover from this situation.
CAUTION
When the RESET button is pressed, ALL settings revert back to the defaults, including the default program (see tables 3 and 4). The RESET button is an unlabeled, recessed button located
behind the door on the right−hand side of the thermostat, below the SETTINGS button (see figure 3). Use a paper clip or small pencil to press the RESET button; ALL thermostat settings will be reset to the defaults listed in the Default Thermostat Settings section.
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 subbase. Pivot the bottom of the thermostat outward (releasing the snaps), then lift up to remove it. To install it, first position the top tilted toward the wall bracket and align it until you feel the tabs and slots engage; then, while the top is in place, pivot the bottom toward the wall until the thermostat snaps into place.
Thermostat Output Table
Table 2 depicts the L3722C thermostat output states for various input conditions. The following notes described the terms used in the table.
Table 2. Thermostat Outputs
| Condition | W1 | W2 | Y1 | Y2 | G |
| Gas Heat, Auto Fan | |||||
| Heat Demand, SMALL | X | ||||
| Heat Demand, LARGE | X | X | |||
| Cool Demand, SMALL | X | X | |||
| Cool Demand, LARGE | X | X | X | ||
| No Demand | |||||
| Gas Heat, Continuous Fan | |||||
| Heat Demand, SMALL | X | X | |||
| Heat Demand, LARGE | X | X | X | ||
| Cool Demand, SMALL | X | X | |||
| Cool Demand, LARGE | X | X | X | ||
| No Demand | X | ||||
| Electric Heat, Auto Fan | |||||
| Heat Demand, SMALL | X | X | |||
| Heat Demand, LARGE | X | X | X | ||
| Cool Demand, SMALL | X | X | |||
| Cool Demand, LARGE | X | X | X | ||
| No Demand | |||||
| Electric Heat, Continuous Fan | |||||
| Heat Demand, SMALL | X | X | |||
| Heat Demand, LARGE | X | X | X | ||
| Cool Demand, SMALL | X | X | |||
| Cool Demand, LARGE | X | X | X | ||
| No Demand | X | ||||
| NOTE − X = output is activated with 24VAC.
NOTE − The temperature ranges expressed in the following def- initions of “SMALL/LARGE” demands are for guidance only; ac- tual temperatures may vary. With a SMALL heat demand, temperature is: below setpoint –0.5F but above setpoint –1.5F AND 30-minute upstage timer HAS NOT expired. With a LARGE heat demand, temperature is: less than setpoint –1.5F OR 30-minute upstage timer HAS expired. With a SMALL cool demand, temperature is: above setpoint +0.5F but below setpoint +1.5F AND 30-minute upstage timer HAS NOT expired. With a LARGE cool demand, temperature is: above setpoint +1.5F OR 30-minute upstage timer HAS expired. |
|||||
Default Thermostat Settings
The default thermostat settings are in table 3 and the default program is shown in table 4.
Table 3. 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 |
| Equipment Protection Timers | Reset Back to Zero |
| Autochangeover | OFF |
Table 4. Default Program Settings (Time/Temp)
| Programs | Time | Temp.− Heat | Temp.− 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 |
Technical Specifications
Thermostat TypeElectronic programmable thermostat for 2−Stage (gas or electric) Heat/2-Stage Cool, non-heat pump, non−power robbing applications.
Table 5. L3722C Terminal Designations
| Terminal | Description |
| R | 24VAC |
| Y1 | First-stage cooling |
| W1 | First-stage heating |
| Y2 | Second-stage cooling |
| W2 | Second-stage heating |
| G | Fan control |
| L | Service Indicator |
| C | 24VAC common |
| T | Outdoor temperature sensor connection 1 |
| T | Outdoor temperature sensor connection 2 |
Power Supply Range18VAC − 30VAC (24VAC nominal),
60Hz
CAUTION
24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the terminals of the connector on the wall bracket.
Also, when working with the thermostat dip switches, use a non−conductive tool, and take caution to avoid making any contact with the circuit board, its imprinted circuitry, and its connector prongs.
Temperature Display Display Scale: Fahrenheit or
- Celsius user selectable (via DIP switch; see figure 18)
- Display range . . . . . . . . . . . . . 35°F (2°C) to 99°F (37°C)
- Display resolution . . . . . . . . . . . . . . . . . . . . . . . . 1°F (1°C)
- Display Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . +/−1°F
If the Fahrenheit/Celsius display must be changed, use a plastic, non−conductive tool to push the dip switch to the right position (see figure 18).
Indoor 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 are sampled every 15 seconds. The displayed temperature is the average of the last four measurements.
Outdoor Temperature Measurement Range
- Measurement Scale . . . . . . . . . . . . . . . . . . . . Fahrenheit
- Measurement Range . . . . . . . . . . . . . . . . −22°F to 122°F
- Measurement Resolution . . . . . . . . . . . . . . . . . . . . . . . 1°F
- Measurement Accuracy . . . . . . . . . . . . . . . . . . . . . . +/−2°F
Temperature Setpoint Range
- Setting range . . . . . . . . . . . . 50°F (10°C) to 90°F (32°C)
- Setting resolution . . . . . . . . . . . . . . . . . . . . . . . . . 1°F (1°C)
- Smart Setback Recovery (via DIP switch #6)
Smart Setback Recovery (SSR) affects the way the thermostat responds to program events. If SSR is disabled, the 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 occurs such that the desired temperature is reached at the time of the the event, not after. Autochangeover Deadband Selection (via DIP switch #7)Autochangeover deadband can be set to 4 or 6 degrees. When autochangeover is enabled (via the AUTO button), the thermostat will automatically change over from heating to cooling and vice versa, to keep the room temperature in between the heating and cooling setpoints. The deadband is the minimum difference between the heating and cooling setpoints. Fan Control AUTO or ON modes, gas or electric heat compatible via DIP switches (also see Thermostat Output section). I/O Relays All thermostat relays are latching type to minimize power consumption.
Equipment Protection Timers
- Minimum Compressor OFF time . . . . . . . . . . . 5 minutes
- Minimum Compressor ON time . . . . . . . . . . . . 4 minutes
- Minimum Furnace ON time . . . . . . . . . . . . . . . 3 minutes
Minimum furnace cycle time (elapsed time between any furnace activation & next furnace activation) 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 overridden 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 minimum equipment cycle timer can be overridden by pressing and holding either the HEAT or COOL button down for 4 seconds.
Over Temperature ProtectionThermal-mechanical
switch opens W1 and W2 at 93°F+/−6°F.
Filter Reminder Settings of Off, 1, 3, 6, or 12 (months
of fan run time) are available. When the programmed time has
elapsed, a FILTER indicator is displayed.
Maintenance Reminder Settings of Off, 6 or 12
(months of chronological time) are available. When the programmed time has elapsed, a maintenance indicator MAINTENANCE” is displayed.
Service Reminder The SERVICE indicator is displayed
only under the following conditions: if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal; OR if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.
Power Loss/Recovery Thermostat memory is retained
for a minimum of 24 hours during a power loss (includes retention of clock setting, program information, HOLD status, programmed temperature setpoint, heat/ cool and fan mode settings, filter reminder status, maintenance reminder status, and equipment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default settings.
IMPORTANT
Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time. LCD BacklightActivated for 30 seconds when any
the button is pressed.
NOTE − During an electrical storm or similar disturbance, the backlight may activate for a few seconds. This is normal and will no longer occur after the electrical disturbance has passed.
- Thermostat Operating Conditions. 35°F to 105°F
- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5% to 90% RH
- Thermostat Storage Conditions . . −40°F to 185°F
- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5% to 95% RH
REFERENCE:
Download Manual:
Lennox L3722C Programmable Thermostat OPERATION MANUAL
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