Lennox C0STAT05FF1L CS3000 Commercial Programmable Thermostat

Product Overview

The Lennox ComfortSense® 3000 Series Commercial Programmable Thermostat, Model C0STAT05FF1L (11Y05), is a 5/2 day programmable and 2-heat / 2-cool electronic thermostat. 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.

This thermostat is suitable for 2-stage heat / 2-stage cool applications using a gas or electric auxiliary heat source and can also be used with an economizer.

Thermostat Display Description: An image shows a Lennox thermostat with a digital display. The display shows the time '12:20', temperature '77°F', and system status indicators. The thermostat has a 'Commercial' label.

Internal vs. Remote Sensor

When a remote indoor sensor is connected and configured, it acts as the room temperature sensor instead of the internal sensor. A dip switch is used to select either the built-in or external remote indoor temperature sensor for temperature control.

General Information

These instructions are intended as a general guide and do not supersede local codes. Consult authorities having jurisdiction before installation. Check equipment for shipping damage. If any damage is found, immediately contact the last carrier.

Initial Thermostat Power-up

When power is initially applied, the thermostat display appears as shown in Figure 1.

Figure 1: Initial Power-Up Display. The thermostat screen shows the current day of the week (MO TU WE TH FR SA SU), time (12:88 AM/PM), programming periods (PROG A B C D HOLD), room temperature (88°), setpoint temperature (88°), and system status indicators for maintenance, filter, service, fan (ON/AUTO), and system mode (COOL/OFF/HEAT).

At this point, the thermostat is fully functional with a default temperature set point of 70°F. If heating equipment is powered and a heat demand is present, the system will begin operating. 'UC' indicates unoccupied, and 'OC' indicates occupied.

Note: The default temperature scale is Fahrenheit but can be reset to Celsius.

Buttons, Backlight, Timers & Settings

Buttons are located behind a small door on the right-hand side of the thermostat (see Figure 2).

Figure 2: Thermostat Buttons. The thermostat face is shown with a small door open, revealing control buttons. These include Heat, Cool, Prog, Day/Time, Fan, Hold, Settings, and Enter. Up and Down arrow buttons are also visible. A label indicates '(DOOR OPEN)'.

Important: Read the following section describing each button before pressing any buttons.

A pale blue display backlight illuminates for 30 seconds each time any button is pressed.

• When PROG or DAY/TIME is pressed, a field begins flashing, expecting input. Changes must be made within 15 seconds, or the HOME screen will return.
• When an Arrow, HOLD, HEAT, or COOL button is pressed, the setpoint and temperature setting appear for 15 seconds. Changes can be made within this time, or the HOME screen will return. The backlight turns off 15 seconds after the HOME screen reappears.

DAY/TIME - Setting the Day and Time

Press the DAY/TIME button to set the current hour, minute, and day of the week:

1. 'AM12' flashes. Use up/down arrows to change the hour. Ensure 'AM' or 'PM' is correct. Press DAY/TIME. For daylight savings, pressing ENTER stores the change and exits to HOME, bypassing minutes and day.
2. Minutes flash. Use up/down arrows to set minutes. Press DAY/TIME.
3. Day 'MO' (Monday) flashes. Use up/down arrows to set the current day (abbreviated as MO, TU, WE, TH, FR, SA, SU). Press DAY/TIME.
4. The HOME screen reappears. Confirm day and time are correct.

HEAT - Using the Heat Mode

Enabling Normal Heat Mode

Use the HEAT button to enable or disable heat mode. If the thermostat is in OFF or COOL mode, pressing HEAT enables Heat mode, indicated by 'HEAT' in the SYSTEM box (Figure 3).

Figure 3: Turn Heat ON/OFF. The thermostat display shows the current time, room temperature, and indicates 'HEAT' in the system status area.

Disabling Heat Mode

If the thermostat is in heat mode, pressing the HEAT button disables it, indicated by 'OFF' in the SYSTEM box (Figure 4).

Figure 4: Heat Mode Disabled. The thermostat display shows the current room temperature and indicates 'OFF' in the system status area.

Heating Demand

The thermostat must be in heat mode for heating equipment control. When the actual temperature is lower than the setpoint, a heating demand is detected, and the heating equipment activates. Heating operation is indicated by a flame icon 🔥 in the SYSTEM box.

When the temperature rises above the setpoint, the flame icon disappears, indicating demand is satisfied and heating is off.

Two timers govern heating restart:

1. Minimum furnace off timer (1.5 minutes for HG).
2. Minimum cycle timer (six minutes).

Example: If heating ran for over six minutes, the minimum cycle timer is fulfilled. For HG (gas), restart is after 1.5 minutes. For HE (electric), it restarts immediately. If heating has not run for six minutes, it makes up the time during the off period, so the lock-out time is never six minutes.

COOL - Using the Cool Mode

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode. If the thermostat is in HEAT or OFF mode, pressing COOL enables cool mode, indicated by 'COOL' in the SYSTEM box (Figure 5).

Figure 5: Turn Cool ON/OFF. The thermostat display shows the current time, room temperature, and indicates 'COOL' in the system status area.

If the thermostat is in cool mode, pressing COOL disables it, indicated by 'OFF' in the SYSTEM box (Figure 6).

Figure 6: Cool Mode Disabled. The thermostat display shows the current room temperature and indicates 'OFF' in the system status area.

Cooling Demand

Set the thermostat to cool mode to control cooling equipment. If the room temperature is higher than the setpoint, a cooling demand is detected, and the cooling equipment activates.

Cooling operation is indicated by flashing snowflake icons ❄ in the SYSTEM box. When the temperature drops below the setpoint, the icons disappear, indicating demand is satisfied and cooling is off.

If a large cooling demand is present, 'Hi' will be displayed in the SYSTEM box (Figure 7).

Note: If no buttons are pressed during a cooling demand, the equipment must operate for at least four minutes. After demand is satisfied, cooling is locked out for five minutes. If another demand occurs during this interval, 'COOL' and snowflakes will flash, but the equipment will not operate until the 5-minute delay has elapsed.

Figure 7: Cooling Demand. The thermostat display shows the current room temperature and indicates 'COOL' and 'HI' in the system status area, with flashing snowflake icons.

HOLD - Using Temperature Hold Modes

When HOLD is displayed on the HOME screen, the thermostat is in a temperature hold condition, ignoring program data and functioning like a non-programmable thermostat.

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired temperature. To adjust it, press the up ↑ or down ↓ arrow buttons. The existing setpoint is displayed to the right of the occupancy mode. Each press adjusts the setpoint by 1 degree.

Figure 8: Hold Temperature Mode. The thermostat display shows the current time, room temperature, and indicates 'HOLD' is active.

After the desired setpoint is reached, the HOME screen reappears after about 15 seconds.

Permanent Hold Mode

At any time, from the HOME screen, set a permanent hold (program override) by pressing the HOLD button (Figure 8). The thermostat functions like a non-programmable thermostat. Use the Up/Down arrows to adjust the hold set point. Press HOLD again to return to the program. Occupancy status remains unchanged.

Temporary (2-Hour) Hold

At any time, from the HOME screen, set a temporary 2-hour hold by pressing the up ↑ or down ↓ arrow buttons until the desired set point is displayed. 'HOLD' flashes (Figure 9). This overrides the program for 2 hours from the last button press, then returns to the program.

To change occupancy status in temporary hold mode, press the ENTER button while HOLD indicator flashes. Occupancy can be set to OC (occupied) or UC (unoccupied).

Figure 9: Temporary Hold Temperature Mode. The thermostat display shows the current time, room temperature, and indicates both 'PROG' and 'HOLD' are active.

While in Temporary Hold, press HOLD once to switch to Permanent Hold (HOLD displays solid; PROG not displayed). Press HOLD again to return to the program (PROG displays; HOLD not displayed).

PROG - Thermostat Programming

The thermostat can be programmed for heating or cooling events for five consecutive days, with four unique events per day. The remaining two days can have a different set of four unique events.

To Change Consecutive Days

Press and hold the PROG button for three seconds. The five consecutive day period is displayed (default: Monday-Friday). Use up/down arrows to change to a different 5-day span (e.g., Saturday-Wednesday).

Figure 10: Change Consecutive days. A visual representation of the days of the week (MO TU WE TH FR SA SU).

Press the PROG button when finished.

To Set Program Events and Temperatures

Figure 11 provides an example of setting programs for a workweek and weekend. Programs A and C reflect desired warmth when occupied (72°F); B allows less heating when unoccupied; D reflects cooler sleeping temperatures. The 2-day graph supports day-long occupancy with a less demanding schedule.

Figure 11: 5/2 Day Program Example. Two bar graphs illustrate typical programming schedules: a 5-day program with periods A, B, C, D showing temperature setpoints for different times of day and occupancy states (occupied, unoccupied, sleep), and a 2-day program with similar periods.

Note: Pressing ENTER during programming saves and exits to the HOME screen.

To program events and temperatures, perform the following steps, once for Cool and once for Heat:

1. Press HEAT or COOL button.
2. Press and release PROG. 'AM 6:00', period 'A', and the 5 consecutive days are displayed; 'AM 6' flashes.
3. Use up/down arrows to select the desired hour; press PROG.
4. Use up/down arrows to select the desired minute; press PROG.
5. Use up/down arrows to select occupancy status (uc/oc); press PROG.
6. Use up/down arrows to select the desired temperature set point; press PROG.
7. Repeat steps 3-6 for periods B, C, and D.
8. Repeat steps 1-7 for the 2-day program.

Note: This thermostat does NOT automatically switch between heating and cooling. Operator involvement is required. At season changes or temperature swings, manually select the opposite conditioning program.

FAN - Controlling the Fan Operation

Use the FAN button to select continuous fan mode or auto fan mode.

To change modes, press the FAN button. A fan icon in the FAN box indicates the fan is running.

If continuous fan mode is enabled ('ON' in FAN box, Figure 12), the fan runs continuously regardless of heating or cooling equipment operation.

Figure 12: Using Fan ON. The thermostat display shows the current time, room temperature, and indicates 'FAN ON' in the fan status area.

If auto fan mode is selected ('AUTO' in FAN box, Figure 13), the fan runs only when heating or cooling equipment is running.

Figure 13: Using Fan AUTO. The thermostat display shows the current time, room temperature, and indicates 'FAN AUTO' in the fan status area.

SETTINGS - Filter/Maintenance Reminders

The thermostat can remind you when the filter needs changing or routine maintenance is required. These reminders are optional and must be activated.

To activate, press the SETTINGS button (below the Fan button in Figure 13) once or twice for the desired reminder (Figure 14, Table 1).

Figure 14: Reminder Settings Display. The thermostat display shows options for setting reminders, including 'OFF', 'MAINT' (Maintenance), and 'FILTER'.

The default setting is OFF (disabled). Use up/down arrows to select desired reminder intervals.

Note: The HOME screen reappears about 15 seconds after the final arrow button press, or press ENTER to store changes and exit.

After a programmed interval elapses, the reminder is displayed (Figure 15).

Figure 15: Reminders. The thermostat display shows a reminder indicator, either 'MAINT' or 'FILTER', active.

After changing the filter or performing maintenance, reset the reminder by pressing the SETTINGS button for four seconds. The screen blinks to indicate the timer has been reset.

Internal/Remote Sensor

If an optional Remote Indoor Sensor (10K) (47W37) is connected, it serves as the room temperature sensor. Dip switch #4 selects between the built-in or external sensor.

Occupied and Unoccupied Modes

During permanent hold mode, the occupancy output follows the program. During two-hour hold mode, the user can change occupancy status (OC/UC) by pressing the ENTER button.

The occupancy relay turns on when the user selects occupancy status during programming. The default state is off. The occupancy relay turns on the economizer.

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (Figure 16). This indicates that the equipment requires service from a qualified service technician.

Figure 16: Service Indicator Flashing. The thermostat display shows the current time, room temperature, and indicates 'SERVICE' is flashing.

Thermostat RESET

Under abnormal conditions, it may be necessary to 'reset' the thermostat to its default condition. This deletes all programming and settings and should only be used when the thermostat fails to function as designed. This can occur after a power surge or electrical disturbance.

Figure 17: Reset Button. An arrow points to a small, recessed button located behind the thermostat's access door, labeled as the reset button.

Caution: When the RESET button is pressed, ALL settings revert to their defaults (see Table 3).

The RESET button is unlabeled and recessed, located behind the door, on the right-hand side of the thermostat, below the SETTINGS button. Use a paper clip or small pencil to press it.

Removing/Installing Thermostat

The thermostat hinges on tabs at the top of the sub-base; no tool is needed for removal. Pivot the bottom of the thermostat outward (releasing snaps), then lift up to remove.

To replace, position the top tilted toward the wall bracket, align tabs and slots, then pivot the bottom toward the wall until it snaps into place.

Default Thermostat Settings

Technical Specifications

Thermostat Type: Electronic programmable thermostat for non-heat pump, 2-stage heat / 2-stage cool.

Power Supply Range: 18VAC - 30VAC (24VAC nominal), 50Hz or 60Hz.

Note on 50Hz: When used in 50Hz applications, tolerance is lowered, leading to slight changes in temperature control accuracy.

Caution: 24VAC is present on the thermostat bracket terminals. Use caution when removing the thermostat from the wall to avoid touching connector terminals. When working with dip switches, use a non-conductive tool and avoid contact with the circuit board or its prongs.

Temperature Display:

• Scale: Fahrenheit or Celsius user selectable.
• Range: 35°F (2°C) to 99°F (37°C).
• Resolution: 1°F (1°C).
• Accuracy: +/-1°F.

Temperature Measurement Range:

• Scale: Fahrenheit.
• Range: 35°F to 99°F.
• Resolution: 0.125°F.
• Accuracy: +/-1°F.
• Field Offset: +/-3°F via DIP switches.

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

Temperature Set Point Range:

• Range: 50°F (10°C) to 90°F (32°C).
• Resolution: 1°F (1°C).

Smooth Setback Recovery (SSR) (via DIP switch #6): Affects thermostat response to program events. If disabled, reacts at event time. If enabled, reacts before event time to reach desired temperature at event time.

Fan Control: AUTO or ON modes.

I/O Relays: Latching type to minimize power consumption.

Terminal Designations

Equipment Protection Timers

• Minimum Compressor OFF time: 5 minutes
• Minimum Compressor ON time: 4 minutes
• Minimum Electric Heat ON time: 3 minutes
• Minimum Furnace ON time: 3 minutes
• Minimum Furnace OFF time: 1-1/2 minutes

Minimum cycle time (for furnace activation): 6 minutes.

Minimum elapsed time between compressor activations: 6 minutes.

Note: All protection timers (except compressor OFF) 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 for four seconds.

Filter Reminder

Settings: Off, 1, 3, 6, or 12 months (of fan run time). When programmed time elapses, a FILTER indicator is displayed.

Maintenance Reminder

Settings: Off, 6, or 12 months (of chronological time). When programmed time elapses, a 'MAINT' indicator is displayed.

Service Reminder

The SERVICE indicator is displayed under these 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 retains program information, HOLD status, setpoint, heat/cool/fan settings, filter/maintenance reminder status, and timers for a minimum of 24 hours during a power loss.

After 24 hours of power loss, programmed settings are lost and replaced with defaults.

Important: Power must be applied for at least six consecutive hours prior to a power loss for memory to be retained for the specified time.

LCD Back Light

Activated for 30 seconds when any button is pressed.

Note: During electrical storms or disturbances, the backlight may activate briefly. This is normal and stops after the disturbance passes.

Thermostat Operating and Storage Conditions

• Operating Conditions: 32°F to 122°F (0°C to 50°C), 10% to 90% RH.
• Storage Conditions: -40°F to 176°F (-40°C to 80°C), 10% to 90% RH.

Internal/Remote Sensor Settings

Figure 18: Internal/Remote Sensor Settings. A diagram shows a set of six dip switches labeled 1 through 6, with a note 'PLUG IN (Use Care To Avoid Bending Prongs.)' and an indicator for 'I/R (internal/remote switch)'.

To select between the internal or remote temperature sensor, use dip switch #4. The default setting is the internal sensor (OFF).