Honeywell T8624D Chronotherm® IV Deluxe Programmable Thermostat

Application

The T8624D Chronotherm® IV Deluxe Programmable Thermostat provides electronic control of 24 Vac multistage heating and cooling systems.

Features

• Full seven-day program capability; different schedules and temperature setpoints may be selected for every day to match the homeowner's flexible schedule.
• Copy key makes programming easier and faster for the installer and homeowner.
• Daylight Savings Time (DST) key for quick change in and out of Daylight Savings Time.
• Models available with programmable fan operation for added homeowner comfort.
• Easy temporary temperature setpoint changes for current period, vacation hold (1 to 255 days) or indefinite hold adds to the homeowner comfort and energy savings.
• Most frequently used keys are located by the Liquid Crystal Display (LCD) for quick and easy access to information.
• Attractive styling complements any decor to the homeowner's delight.
• Backlighting the large display makes the LCD very easy to read.

Product Data

• Models available with outdoor temperature sensor capability for homeowner convenience. The sensor is also more accurate than a thermometer.
• Configurable features allow one model to be used to replace many different models (less inventory, no longer need to carry separate models to get these features). Features include: °F or °C temperature display; automatic or manual changeover; electric or conventional heat fan operation; adjustable heating cycle rate.
• Minimum off time for cooling compressors and heat pumps protects the equipment and extends the equipment life.
• Easy installation, setup, and system test saves installer time and increases productivity.
• System test simplifies troubleshooting and saves time by overriding the time delays.
• Adaptive Intelligent Recovery® control brings the room temperature to the temperature setpoint at the programmed time, maximizing comfort and energy savings.
• Setpoints are permanently held in memory (no batteries used) and retained during power outages for increased installer and homeowner convenience.
• Universal Versaguard™ Thermostat guards available for added security.

Specifications

Thermostat Model

T8624D Thermostats provide features listed in Table 1.

Electrical Rating (Nominal Range)

24 Vac, 50/60 Hz. 20 to 30 Vac, 50/60 Hz.

Batteries

No batteries required.

Loss of Power

The thermostat will maintain programmed times and temperatures for the life of the product. The clock and day information is retained for a minimum of thirty minutes.

System Current Load Ratings

6 VA maximum at 30 Vac, 50/60 Hz.

Output Relay Draw

See Table 2.

Temperature Ratings

Operating Ambient: 40°F to 110°F (4°C to 43°C). Shipping: -30°F to +150°F (-34°C to +65°C).

Display Accuracy

±1°F (±0.5°C).

Setpoint Range

Heating: 40°F to 90°F (7°C to 31°C). Cooling: 48°F to 99°F (9°C to 37°C). Differential: 3°F (1.5°C). Default Settings: see Table 3.

Minimum Stage Operation Time

Minimum On (Heat and Cool) (select models): factory setting 2 minutes; option 0 minutes. Minimum Off (Cool and Heat Pump): factory setting 2 minutes; option 0 minutes.

Humidity Ratings

5% to 90% RH, noncondensing.

Clock Accuracy

±1 minute per month.

Finish

Taupe or Premier White® color.

Ordering Information

When purchasing replacement and modernization products from your TRADELINE® wholesaler or distributor, refer to the TRADELINE® Catalog or price sheets for complete ordering number.

Contact Information

If you have additional questions, need further information, or would like to comment on our products or services, please write or phone:

1. Your local Home and Building Control Sales Office (check white pages of your phone directory).
2. Home and Building Control Customer Relations, Honeywell, 1885 Douglas Drive North, Minneapolis, Minnesota 55422-4386

In Canada—Honeywell Limited/Honeywell Limitée, 35 Dynamic Drive, Scarborough, Ontario M1V 4Z9. International Sales and Service Offices in all principal cities of the world. Manufacturing in Australia, Canada, Finland, France, Germany, Japan, Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A.

Installation

When Installing this Product

1. Read these instructions carefully. Failure to follow the instructions can damage the product or cause a hazardous condition.
2. Check the ratings given in the instructions and on the product to make sure the product is suitable for your application.
3. Installer must be a trained, experienced service technician.
4. After completing installation, use these instructions to check out the product operation.

Location

Install the thermostat about 5 ft (1.5m) above the floor in an area with good air circulation at average temperature. See Fig. 2.

Do not install the thermostat where it can be affected by:

• Drafts, or dead spots behind doors and in corners.
• Hot or cold air from ducts.
• Radiant heat from sun or appliances.
• Concealed pipes and chimneys.
• Unheated (uncooled) areas such as an outside wall behind the thermostat.

Diagram: Typical location of thermostat (Fig. 2)

This diagram illustrates the recommended placement of the thermostat approximately 5 feet (1.5 meters) above the floor in an area with good air circulation, away from direct heat sources, drafts, or dead spots.

Wallplate Installation

The thermostat can be mounted horizontally on the wall or on a 2 in. x 4 in. wiring box. Position wallplate horizontally on the wall or on a 2 in. x 4 in. wiring box.

1. Position and level the wallplate (for appearance only). The thermostat will function properly even when not level.
2. Use a pencil to mark the mounting holes. See Fig. 3.
3. Remove the wallplate from the wall and drill two 3/16 inch holes in the wall (if drywall) as marked. For firmer material such as plaster, drill two 7/32 inch holes. Gently tap anchors (provided) into the drilled holes until flush with the wall.
4. Position the wallplate over the holes, pulling wires through the wiring opening.
5. Loosely insert the mounting screws into the holes.
6. Tighten mounting screws.

Diagram: Dimensions of thermostat (Fig. 1)

This diagram shows the physical dimensions of the thermostat in inches (mm), including width (3-5/8 in.), height (2-3/4 in.), and depth measurements.

Mounting Means

The thermostat mounts on a wallplate. The wallplate mounts horizontally on a wall or outlet box with two no. 6 x 32 screws (included).

Accessories

• C7089B Outdoor Temperature Sensors (69-1020).
• Universal Versaguard™ Thermostat guards.

Recycling Notice

If this control is replacing a control that contains mercury in a sealed tube, do not place your old control in the trash. Contact your local waste management authority for instructions regarding recycling and the proper disposal of the old thermostat.

Wiring

All wiring must comply with local electrical codes and ordinances. Follow equipment manufacturer wiring instructions when available. Refer to Fig. 14 for typical hookup. A letter code is located near each terminal for identification. Refer to Table 4 for terminal designations.

Diagram: Mounting the wallplate (Fig. 3)

This diagram illustrates the process of mounting the wallplate, showing wires passing through the wall, wall anchors, and mounting screws.

CAUTION: Disconnect power before wiring to prevent electrical shock or equipment damage.

1. Loosen the terminal screws on the wallplate and connect the system wires. See Fig. 4.

IMPORTANT: Use 18 gauge, color-coded thermostat cable for proper wiring.

2. Securely tighten each terminal screw.
3. Push excess wire back into the hole.
4. Plug the hole with nonflammable insulation to prevent drafts from affecting the thermostat.

Diagram: Proper wiring technique (Fig. 4)

This diagram shows two methods for connecting wires to thermostat terminals: for wraparound insertion strip (7/16 in.) and for straight insertion strip (5/16 in.).

a Some OEM models label the terminal for transformer common B.

Diagram: Mounting thermostat on wallplate (Fig. 5)

This diagram shows how to attach the thermostat to the wallplate by engaging the tabs at the top and pressing the lower edge to latch.

Settings

Using Thermostat Keys

The thermostat keys are used to:

• Set current day and time.
• Program times and setpoints for heating and cooling.
• Temporarily override program temperatures.
• Display present setting.
• Configure Installer Setup.
• Check System Test.
• Display outdoor temperature (select models).
• Set the system operation.
• Set the fan operation.

See Fig. 6 for the location of the keys.

System and Fan Settings

The system default setting is Heat and the fan default setting is Auto. Use the System and Fan keys or switches to change the settings. See Fig. 7. The fan settings can be set for each program period individually. The system selection is for all the program periods.

System settings control the thermostat operation as follows:

• Heat: The thermostat controls the heating.
• Off: Both the heating and cooling are off.
• Cool: The thermostat controls the cooling.
• Auto: The thermostat automatically changes between heating and cooling operation, depending on the indoor temperature.

Fan settings control the system fan as follows:

• On: Fan operates continuously.
• Auto: Fan operates with equipment.

Diagram: System and Fan key locations (Fig. 7)

This diagram shows the location of the System and Fan keys on the thermostat.

Diagram: Key locations and descriptions (Fig. 6)

This diagram labels all the keys on the thermostat and provides a description of their functions, including setting time, programs, hold modes, system/fan operations, and display information.

Installer Setup

NOTE: For most applications, the thermostat factory settings will not need to be changed. Review the factory settings in Table 6 and if no changes are necessary, go to the Installer System Test section.

The Installer Setup is used to customize the thermostat to specific systems. Some of the options include temperature display, changeover, and outdoor temperature display. Installer Setup numbers are listed in Table 6. The table includes all the configuration options and the factory settings for the thermostat.

A combination of key presses are required to use the Installer Setup feature.

• To enter the Installer Setup, press and hold the Information i key with the increase ▲ and decrease ▼ keys until the first number is displayed. All display segments appear for approximately three seconds before the number is displayed. See Fig. 8 and 9.
• To advance to the next Installer Setup, press the Time ► key.

NOTE: To scroll the Installer Setup numbers backwards, press the Time ◄ key.

NOTE: To exit the Installer Setup, press Run Program.

Diagram: Display of Installer Setup number and setting (Fig. 9)

This diagram shows the display format for Installer Setup, indicating where the setup number and its corresponding factory or other choice setting are shown.

Diagram: Display of all the segments of the LCD (Fig. 8)

This diagram shows the thermostat's LCD display with all segments illuminated, typically seen during initialization or system tests.

CAUTION: Electric heat systems must be configured to 1 in Installer Setup number 2 to prevent equipment damage caused by the system running without the fan.

IMPORTANT: Only configurable numbers are shown on the device. Example: If thermostat does not have a system key, Installer Setup Number 12 will not be displayed. Review Table 6 factory settings and mark any desired changes in the Actual Settings column. When Installer Setup is complete, review the settings to confirm that they match the system.

^a The cycle rate for the last stage of heat is adjustable with 6 cph being the factory setting.

IMPORTANT: Review the settings to confirm that they match the system. Press Run Program to exit the Installer Setup. The thermostat has saved the Installer Setup changes and initiated a reset in order to operate with these new settings. Be sure to set the current day and time immediately.

Setting Current Day and Time

1. Press Set Current Day/Time.

NOTE: On initial power up or after an extended power loss, 1:00 pm flashes on the display until a key is pressed.

Diagram: Setting Current Day/Time (Page 9)

Illustrates pressing the 'Set Current Day/Time' button, showing the initial display of '1:00PM' and then 'Tue' for the day.

2. Press Day until the current day is displayed.

NOTE: Sun=Sunday, Mon=Monday, Tue=Tuesday, Wed=Wednesday, Thu=Thursday, Fri=Friday, Sat=Saturday.

Diagram: Selecting the Day (Page 10)

Shows pressing the 'Day' button to cycle through the days of the week.

3. Press Time ◄ or Time ► until the current time is displayed.

NOTE: Tapping the Set Current Day/Time will change the time in one hour increments.

Diagram: Setting the Time (Page 10)

Shows pressing the 'Time' buttons to adjust the hour and minute.

NOTE: If the current time is Daylight Savings Time, press Daylight Time until DST is displayed.

4. Press Run Program.

Diagram: Finalizing Day/Time Settings (Page 10)

Shows the display after setting the day and time, and pressing 'Run Program'.

Installer System Test

Use the Installer System Test to check the thermostat operation. Refer to Table 7 for a list of the available system tests.

To start the system test:

CAUTION: The minimum off time for compressors is bypassed during the Installer System Test. Equipment damage can occur if the compressor is cycled too quickly.

Press and hold the increase ▲ and decrease ▼ keys, at the same time, until 10 appears. All segments of the display are displayed for three seconds before 10 appears. See Fig. 10 and 11.

Diagram: Display of all the segments of the LCD (Fig. 10)

This diagram shows the thermostat's LCD display with all segments illuminated, indicating initialization for the Installer System Test.

Diagram: Display of test number (Fig. 11)

This diagram shows the 'TEST NUMBER' display on the thermostat, indicating the current test being run.

Refer to Table 8 for the directions and results of the specific tests.

NOTE: Press Time ► to advance to the next test and Time ◄ to go to the previous test. Press Run Program to exit the system test.

Thermostat Information

1. Press the Time ◄ key to access the thermostat information.
2. Press the increase ▲ key to display the production date code. The first two large digits are the month and the third digit is the last digit of the year (Example: 027=February 1997).
3. Press the increase ▲ key again to display the software identification code. (Example: 02 = software ID code 2)
4. Press the increase ▲ key again to display the software revision number (Example: 001=Revision number 1).
5. Press the increase ▲ key again to display the EEPROM identification code. (Example: 314 = EEPROM ID 314)
6. Press the Run Program key to exit the system test. The system test times out after four minutes without any key presses.

Programming

The keyboard is located behind the thermostat cover with three frequently used keys by the display. The thermostat display shows day, time, program period, temperature, system and fan operation selection.

The thermostat can be set for four times and up to eight temperatures for each day of the week (28 independent time and 56 temperature settings). The ▲ and ▼ keys provide quick temporary temperature changes to increase comfort. The Hold Temp key provides energy efficient operation for extended periods of time.

Before starting the programming procedure, use Table 9 to organize the program schedule. The factory preprogrammed time, temperature and fan settings are shown in brackets. If a daytime energy savings period is not used, press the period key (Leave or Return) until the time is blank. The fan setting feature is available on select thermostat models.

Setting the Current Day and Time

IMPORTANT: Always press the keys with your fingertip or similar blunt tool. Sharp instruments like pens and pencil points can damage the keyboard.

1. Press Set Current Day/Time.

NOTE: On initial power up or after an extended power loss, 1:00 pm flashes on the display until a key is pressed.

Diagram: Setting Current Day/Time (Page 9)

Illustrates pressing the 'Set Current Day/Time' button, showing the initial display of '1:00PM' and then 'Tue' for the day.

2. Press Day until the current day is displayed.

NOTE: Sun=Sunday, Mon=Monday, Tue=Tuesday, Wed=Wednesday, Thu=Thursday, Fri=Friday, Sat=Saturday.

Diagram: Selecting the Day (Page 10)

Shows pressing the 'Day' button to cycle through the days of the week.

3. Press Time ◄ or Time ► until the current time is displayed.

NOTE: Tapping the Set Current Day/Time will change the time in one hour increments.

Diagram: Setting the Time (Page 10)

Shows pressing the 'Time' buttons to adjust the hour and minute.

NOTE: If the current time is Daylight Savings Time, press Daylight Time until DST is displayed.

4. Press Run Program.

Diagram: Finalizing Day/Time Settings (Page 10)

Shows the display after setting the day and time, and pressing 'Run Program'.

Programming the First Day

Start by programming the Wake time and temperature (and fan operation on select models) for any one day:

1. Press Wake.

Diagram: Programming Wake Time and Temperature (Page 13)

Illustrates pressing 'Wake', selecting the day, setting the time, and adjusting the temperature using the increase/decrease keys.

2. Press Day until the desired day is displayed.

NOTE: The program times are in fifteen minute intervals. (Example: 8:00, 8:15, 8:30).

3. Press Time ◄ or Time ► until the desired Wake time is displayed.

NOTE: The setpoint temperature range is 40 to 90°F (7 to 31°C) for heating and 45 to 99°F (9 to 37°C) for cooling.

4. Press increase ▲ or decrease ▼ key until the desired Wake temperature is displayed.

NOTE: Press Fan to modify fan operation. Auto means the fan will run only when the heating or cooling equipment is operating. On means the fan will run continuously for the entire period.

Copying a Day

NOTE: The thermostat must be in the program mode to use the copy feature. Go to step 2 if the thermostat is already in the program mode.

1. Press Wake.
2. Press Day to select the day to be copied if different from the day displayed.
3. Press Copy.
4. Press Day until the day to be copied to is displayed.
5. Press Copy.

NOTE: 'donE' will be displayed for two seconds and then the normal program display will be shown.

6. Repeat steps 2 through 5 for all the days desired.
7. Press Run Program.

Clearing Program Period

NOTE: The thermostat must be in the program mode to use the clear feature. Go to step 2 if the thermostat is already in the program mode.

1. Press Wake, Leave, Return or Sleep.
2. Press Day until the desired day is displayed.
3. Press Leave, Return or Sleep until the start time and temperature setting are cleared (approximately 3 seconds).

NOTE: Wake cannot be cleared.

4. Repeat steps 2 and 3 for all the periods to be cleared.
5. Press Run Program.

Setting Temporary Temperatures

Changing Temperature Setting Until the Next Program Period

Press increase ▲ or decrease ▼ key until the desired temperature setpoint is displayed.

NOTE: If ▲ or ▼ appear under the temperature display, it means that both the heating and cooling setpoints are being adjusted. Tapping the key will change both the heat and cool setpoints by one degree. Press i after the desired setpoint is reached to check the setpoints.

Diagram: Temporary Temperature Setting (Page 15)

Shows the display changing from setpoint to room temperature after approximately 3 seconds.

NOTE: The temporary temperature setting is displayed for approximately 3 seconds. The setting is canceled when the next period starts or when Run Program is pressed.

Changing Temperature Setting Indefinitely

1. Press Hold Temp.
2. Press increase ▲ or decrease ▼ key to change the setting, if desired.
3. Press Heat/Cool Settings to change between heat and cool settings.
4. Press increase ▲ or decrease ▼ key to adjust temperature settings.

NOTE: When the System is set for Auto, both heat and cool settings are needed. If the System is set for Heat, only the Heat setpoint is needed or if Cool is selected, only the Cool setpoint is needed.

Changing Temperature Setting Until a Designated Day and Period

1. Press Hold Temp twice.
2. Press Time ◄ or Time ► until the desired number of days is displayed (1 to 256 days). (Example: 18 = Hold will override the daily programs for 18 days)
3. Press Wake, Leave, Return or Sleep to select the period the program will start. (Example: Return = thermostat will stop the Hold at the Return period start time)
4. Press increase ▲ or decrease ▼ key to adjust the temperature setting, if desired. (Example: Heat 54° = heating equipment will operate when the room temperature is below 54°F)
5. Press Heat/Cool Settings to change between heat and cool settings.
6. Press increase ▲ or decrease ▼ key to adjust the temperature setting, if desired. (Example: Cool 84° = cooling equipment will operate when the room temperature is above 84°F)

NOTE: In this example, the thermostat uses the Hold setting for eighteen days and returns to the daily programs at the Return period start time. The temperature settings are heating 54°F and cooling 84°F. Only the heating temperature is used because the System is set for Heat. The thermostat will use both the heating and cooling temperature settings when the System is set to Auto.

IMPORTANT: If the Hold needs to be canceled before the designated time, press Run Program to return to the program.

Setting Temporary Fan Operation

Press Fan until the desired fan operation is selected. This fan setting will be in effect until the next regularly scheduled period starts.

Using Daylight Savings Time Feature

This feature allows you to change in and out of Daylight Savings Time with a key press. When Daylight Time is pressed in the fall, the time will go back one hour. In the spring, the time will go ahead one hour and the display will show DST. See Setting the Current Day and Time section for initial setting instructions.

NOTE: Pressing Daylight Time more than once within a five minute period will scroll you through various time options (example: one hour earlier or later with or without DST). Pressing Daylight Time six times in a five minute period will return you to your original settings.

Diagram: Daylight Time key (Page 16)

Shows the 'Daylight Time' key and the thermostat display indicating DST.

Displaying the Outdoor Temperature

If your thermostat is equipped with an outdoor sensor, you can check the temperature at the sensor by pressing i once.

Diagram: Information key (Page 16)

Shows the 'i' (Information) key and the thermostat display showing an outdoor temperature reading.

Operation

P+I Control

The thermostat microprocessor-based control requires that the user understands temperature control and thermostat performance. A conventional electromechanical or electronic thermostat does not control temperature precisely at setpoint. Typically, there is an offset (droop) in the control point as the system load changes. This is a phenomenon that most people in the industry know and accept. Many factors contribute to offset including switch differential, thermal lag, overshoot, cycle rates, and system load.

The thermostat microprocessor simultaneously gathers, compares, and computes data. Using this data, it controls a wide variety of functions. The special proprietary algorithm (program) in the thermostat eliminates the factors causing offset. This makes temperature control more accurate than conventional electromechanical or electronic thermostats. The temperature control algorithm is called proportional plus integral (P+I) control.

The thermostat sensor, located on the thermostat or remote, senses the current space temperature. The proportional error is calculated by comparing the sensed temperature to the programmed setpoint. The deviation from the setpoint is the proportional error.

The thermostat also determines integral error, which is a deviation based on the length of error time. The sum of the two errors is the (P+I) error. The cycle rate used to reach and maintain the setpoint temperature is computed using the P+I. The addition of the integral error is what differentiates the thermostat from many other electronic and electromechanical thermostats. See Fig. 12.

Diagram: Proportional temperature control versus P+I temperature control (Fig. 12)

This graph compares Proportional control with P+I control. The Y-axis represents Temperature, and the X-axis represents Percent Load. It illustrates how P+I control maintains temperature closer to the setpoint by minimizing offset.

Operation Sequence

The thermostat energizes specific terminals depending on what the Fan and System are set to. The LCD will display the time, room temperature, system, and fan selection. Symbols will be displayed when the heating, cooling, or fan is energized. See Table 10 for specific information.

NOTE: Not all thermostat models have all the terminals listed in the Energize column.

^a G is energized and fan symbol is displayed on duel fuel models when set for electric heat.

^b Based on last piece of equipment called (cooling = O or heating = B) and Installer Setup selection.

Equipment Protection

As part of the operational sequence, the thermostat microprocessor also incorporates minimum off time for all heating and cooling stages. Using the minimum off time assures that rapid cycling of equipment does not occur, which extends equipment life. Minimum off times are set in the Installer Setup.

Thermostat Operation Startup

When power to the thermostat is turned on, a startup and initialization program begins. The startup occurs only on initial powerup. After total loss of power for an extended period, the current time and day may need to be set, but the user program is held. See Table 11 for the default values.

NOTE: Immediately following initialization, the user can enter new setpoints to be used in place of the default values.

Adaptive Intelligent Recovery® Feature

Adaptive Intelligent Recovery® control assures that the comfort setting is achieved at the programmed time regardless of weather conditions. Conventional recovery, however, starts recovery at the beginning of the programmed time period and used the equipment to achieve the comfort settings as soon as possible.

Adaptive Intelligent Recovery® control calculates the recovery ramp based on the number of degrees away from the desired setpoint, previous equipment performance, and weather history to initiate recovery at the optimal time to achieve the comfort setting at the desired time.

Once the recovery ramp is intersected, the setpoint changes from the setback setpoint to the comfort setpoint. This change snaps on both stages of the equipment and runs both stages until the setpoint is reached. If the setpoint is reached too early or too late, the ramp is adjusted for the next days' recovery. See Fig. 13.

Diagram: Gradual temperature change in recovery (Fig. 13)

This graph illustrates a gradual temperature change in recovery mode for heating, showing the Setpoint Temperature and Actual Temperature over time during SLEEP and WAKE periods.

Troubleshooting Guide

Refer to Table 12 for troubleshooting information.

^a Available on select models.

Cross Reference

Refer to Table 13 for thermostat cross referencing information.

Wiring Diagram

Diagram: Typical hookup of T8624D in multistage system (Fig. 14)

This wiring diagram shows the typical hookup of the T8624D thermostat in a multistage system. It illustrates connections to thermostat terminals (RC, Y1, G, O, Y2, C, B, W2, W1, R, OT) and to cooling and heating transformers, fan relay, compressor contactors, and heat relays. It also notes specific wiring requirements like jumping RC to R for single transformer systems and the use of Y2 for heat pump systems.