Honeywell TB6575/TB8575 Digital Fan Coil Thermostats Installation Guide

Honeywell TB6575/TB8575 Digital Fan Coil Thermostats

PRODUCT DESCRIPTION

The TB6575 and TB8575 are a family of Digital Fan Coil thermostats for residential and commercial applications such as hotels, condominiums, school classrooms, etc.
Four models are available for your application:

• TB6575A1016 – 2-pipe or 4-pipe with seasonal/manual/automatic heat/cool changeover; 120/240 Vac.
• TB6575B1000 – 2-pipe only with seasonal or manual heat/cool changeover; 120/240 Vac.
• TB6575C1016 – 2-pipe or 4-pipe with seasonal/manual/automatic heat/cool changeover; 120/240/ 277 Vac.
• TB8575A1016 – 2-pipe or 4-pipe with seasonal heat/cool changeover; 24Vac.

All four models are suitable for multiple applications. Changes in output wiring and external links between wiring terminals allow you to configure the thermostat for the appropriate application.
The applications that are available are:

• Heating or Cooling only
• Two pipes: Heat or Cool with Manual Changeover
• Two pipes: Heat or Cool with Seasonal Changeover (requires optional pipe sensor)
• Two pipes: Heat or Cool with Auxiliary Heat and Manual or Seasonal Changeover (requires optional pipe sensor)
• Four pipes: Mixed Manual and Auto Changeover
• Four pipes: Manual Changeover
• Four pipes: Auto Changeover

The fan is controlled from the thermostat. The Low, Medium, High, or Auto fan settings are easily made with a press of a key.
Valves and auxiliary electric heaters can be controlled using a relay or contactor controlled by the system switch.

FEATURES

• Simple, intuitive user interface.
• Pre-installed lead wires for fast installation (TB6575A, TB6575B and TB6575C models only)
• Backlight display permits easy viewing in any light.
• Four buttons allow manual control of system operation, fan speed, and temperature setpoint adjustment.
• Digital display of ambient temperature, setpoint, heating or cooling mode, fan status, and remote setback
• Proportional plus Integral (P+I) control algorithm for precision temperature regulation.
• Single Setpoint and Heat/Cool setpoint methods for 4-pipe auto changeover.
• Adjustable maximum heating and minimum cooling setpoint limits using range stops.
• EEPROM permanently retains user settings, including setpoints, during power loss (no batteries required).
• Selectable °C or °F display via Setup button on thermostat.
• Displayable pipe sensor temperature readout to aid in troubleshooting.
• Selectable to allow the fan motor to always begin on high speed to ensure sufficient torque at startup.
• Option to wire a remote indoor temperature sensor.
• Freeze protect algorithm turns on heat when needed.
• Economy Setback options via dry contact or Activity Sensing
• Advanced fan control with VersaSpeed™ fan ramp algorithm and Auto Fan Reset .

SPECIFICATIONS

Supply Voltages:

TB6575A1016 and TB6575B1000:

• 120 Vac ±10% at 50/60Hz
• 240 Vac -15% to +10% at 50/60Hz

TB6575C1016:

• 120 Vac ±10% at 50/60Hz
• 240 Vac -15% to +10% at 50/60Hz
• 277 Vac ±10% at 50/60Hz

TB8575A1016:
20 to 30 Vac at 50/60Hz (using 24 Vac, Class 2, NEMA rated transformer)

Safety Fuse: 15 A, 350V. If the safety fuse blows, the thermostat must be replaced. The fuse is not field replaceable.

Electrical Ratings: (see Table 1).

Environmental Ratings:

Temperature:
Operating Range: 18°C to 49°C (0°F to 120°F).
Shipping and Storage Range: -29°C to 49°C (-20°F to 120°F).
Humidity: 5% to 90% RH, non-condensing.

Onboard Temperature Sensor:
Type: 10K NTC
Working Range: 18°C to 49°C (0°F to 120°F)
Display Range: 0°C to 37°C (32°F to 99°F)
Accuracy ±2.0°F at 70°F

Remote Temperature Sensor (optional):
Type: 20K NTC
Working Range: 18°C to 49°C (0°F to 120°F)
Display Range: 0°C to 37°C (32°F to 99°F)
Accuracy ±2.0°F at 70°F

Remote Pipe Sensor (optional):
Type: 20K NTC
Working Range: 0°C to 93°C (32°F to 199°F)
Display Range: 0°C to 93°C (32°F to 199°F)
Accuracy ±5.0°F over the temperature sensing range

Remote Setback Input: Dry contact, maximum resistance of 100 ohms. TB6575 – 9Vdc, < 4 mA; TB8575 – 16 Vdc, < 5 mA. Note Electrical WARNING on page 3.

Remote Setback Range:
Heating: 10°C to 21°C (50°F to 70°F).
Cooling: 22°C to 32°C (72°F to 90°F).

Enclosure: Plastic (cover, sub-base, and optional adaptor plate)

Junction Box Mounting: Direct mounting on a horizontal single gang NEMA 2 x 4 in. surface mount electrical box, or on 4 x 4 in. box or vertical 2 x 4 in. surface mount electrical box with the optional 50033847-001 adapter plate.
Dimensions: See Fig. 1 .
Wiring: 11 screw-in terminals located on the sub-base capable of accepting up to 2 x 18 AWG (0.8 sq. mm), 1 x 16 AWG (1.3 sq. mm), or 1 x 14 AWG (2.1 sq. mm) wires. Accepts stranded or unstranded 14-28 gauge wire.

NOTES:

1. The TB6575A1016 and TB6575C1016 models are pre-fitted with color-coded fly leads (16 AWG) attached to seven terminals.
2. The TB6575B1000 model is pre-fitted with colorcoded fly leads (16 AWG) attached to six terminals.
3. The TB8575A1016 model does not have fly leads attached to any terminals.
4. See Table 3 on page 5 for fly lead usage.

Minimum Operational Life (at maximum load): Thermostat contacts: 100,000 cycles

Approvals:
CSA Certified C/US for Canada and the U.S.A. Meets the same requirements as UL-873 and UL 1/4 HP.
FCC Part 15 Class B

Accessories:

• 50033847-001 – Adapter plate for mounting on a vertical 2 x 4 in. single-gang or double-gang NEMA standard vertical switch box (6 1/4 in. (158 mm) x 5 1/ 16 in. (128 mm) x 13/22 in. (10 mm)).
• TR21 – 20K Ohm NTC Non-Linear Remote temperature sensor.
  Other acceptable remote temperature sensors are —
  • 20K Ohm: C7041B2005, C7041B2013, C7041C2003, C7041P2004, C7770A1006, C7772A1004, and C7772A1012
  • 10K Ohm (for averaging only): TR21-A
• PS20 (535-34AB08-203) – Remote pipe sensor (20K Ohm)
• W6380B1005 – Fan Coil Unit Relay Control Center
• WSK-24 – Wireless Occupancy Solution (Receiver, occupancy sensor and door sensor)

Models, applications, and features: Table 2 identifies the applications and features of each model.

Table 2. Applications and Features

• The five relays are wired via terminals W, Y, Gh, Gm, and Gl. Relay 1 controls Heat open (W) or Cool open (Y). Relay 2 controls Cool open or Electrical heater output (Y/A). Relays 3, 4, and 5 control the High, Medium, and Low fan speeds respectively (Gh, Gm, and Gl).
  NOTE: In 2-pipe configurations without Auxiliary Heat, only 4 relays are used; relay 2 (Y/A) is not used.
• Pipe sensor is required for 2 pipe auto changeover and 2 pipe auxiliary heat applications.

INSTALLATION

When Installing this Product…

1. Read these instructions carefully. Failure to follow them could 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 and experienced service technician.

WARNING:
Risk of electrical shock.
Can cause severe injury, property damage or death.
Disconnect power supply before installation and before servicing.

IMPORTANT:
The thermostats are line voltage powered devices. All wiring must comply with national and local electrical codes, ordinances and regulations. Provide disconnect means and overload protection, as required.
The TB8575A1016 thermostat must be powered by an Approved 24 Vac, Class 2, NEMA rated transformer (such as a W6380 Relay Control Center).

Location
The thermostats are the temperature control element in a fan coil or air-conditioning system. They must be located about 1.5m (5 ft.) above the floor, in a position with good air circulation, to sense room temperature.

MPORTANT
Do not mount the device where it can be affected by:

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

Mounting and Wiring

CAUTION
Equipment damage hazard. Operation at low temperatures can cause fan coil damage.

This thermostat is not a safety device. Do not use it where the space temperature is outside of the device operating range.
A display of two dashes, – –, for the Room Temp display indicates a sensor failure or a temperature outside of the thermostat operating range of 18°C to 49°C (0°F to 120°F). With – – displayed, the thermostat ceases to operate. When the temperature returns to within its operating limits, the thermostat returns to operation.
The optional freeze protect feature should be used if low temperatures can occur.

The thermostat must be mounted flush to the wall. The thermostat can be mounted directly to a 2 x 4 in.
horizontal junction box (see Fig. 2 ). An optional adaptor plate (50033847-001) can be used with a 4 x 4 in. or a vertical junction box for which mounting screws are supplied (see Fig. 3 ).

1. Prepare the supply wires:
   • Mounting on a 4 x 4 in. or vertical 2 x 4 in. junction box:
     • Feed the supply wires through the junction box and the opening in the adaptor plate.
     • Affix the adaptor plate to the junction box using the screws provided.
   • Mounting on a horizontal 2 x 4 in. junction box: Feed the supply wires through the opening of the junction box.
2. Attach the supply wires:
   • For the TB6575A1016,TB6575B1000 and TB6575C1016 models:
     • Push the fly lead wires through the wiring access hole in the sub-base.
     • Attach the fly lead wires to the supply wires using wire nuts (not provided).See Table 3 on page 5 for terminal and lead identification.
     • Push the fly lead and supply wires back into the junction box.
   • For the TB8575A1016 model (which does not have pre-wired fly leads):
     • Attach the supply wires directly to the terminals on the sub-base. See Table 3 on page 5 for terminal identification.
     • Push the supply wires back into the junction box.
3. Mount the sub-base:
   • Mounting on a 4 x 4 in. or vertical 2 x 4 in. junction box: Align the two holes at the top edges of the subbase with the two pins on the adaptor plate.
     Attach the sub-base to the adaptor plate using the screws provided.
   • Mounting on a horizontal 2 x 4 in. junction box: Attach the sub-base to the junction box using the screws provided.
4. Thoroughly check the wiring to the sub-base before finally mounting the thermostat on the wall.
5. Center the thermostat body over the sub-base, and press down firmly to engage the four tabs on the sub-base and snap the thermostat body into place.
6. Use the provided safety screw to secure the thermostat main body to the sub-base.
7. If using the adaptor plate, press the adaptor plate screw cover into place.

Terminal Wiring

Table 3 provides the terminal wiring for each model and application.

NOTE: The TB6575A1016,TB6575B1000 and TB6575C1016 models have color coded fly leads attached to the terminals. Refer to Table 3 for the color codes.
The Terminal Identifiers in Table 3 have the following meaning:

• C: Common 24 Vac
• Gh: High speed fan relay
• Gl: Low speed fan relay
• Gm: Medium speed fan relay
• L: Line voltage power (120/240/277 Vac)
• N: Line voltage ground (120/240/277 Vac)
• Ps: Pipe sensor (optional)
• R: 24 Vac power
• Rs: Remote sensor (optional)
• SB: Remote setback (optional)
• Sc: Ground (required if remote sensor, pipe sensor, and/or remote setback are connected)
• W/Y: W = Heating; Y = Cooling (2 pipe only)
• Y/A: Y = Cooling; A = Electrical heater output

Table 3. Terminal Wiring.

• Rs; Remote sensor is optional.
• Required when Rs, SB, or Ps is wired.
• SB; Remote setback is optional.
• Pipe sensor: Discrete, Analog, or Aquastat®.
• These terminals (8, 9, 10, and 11) do not have lead wires attached to them.
• A check mark (ü) indicates the terminal is used in that application. Rs and SB terminal connections are optional. If a terminal is left blank, it is not used in that application.
• O = Optional
• R = Required if Rs, SB, or Ps is wired.
• Terminal 3 is not used on the TB6575B1000 model.
• The TB8575A1016 model does not have fly lead wires attached to any terminals.

Accessory Wiring

Remote Pipe Sensor Wiring
The remote pipe sensor is used for 2 pipes auto and 2 pipes heat and cool with auxiliary heat changeover. The pipe sensor will sense the temperature in the pipes to tell the thermostat when the system is set for Heat or Cool.

1. Check Installer Setup Number (IS) 5 to ensure it is set to the desired value. (See Table 4 on page 11).
2. Wire pipe sensor to Sc and Ps terminals.
3. Attach pipe sensor to the pipe.
4. Insulate pipe sensor, as necessary.
5. Change pipe sensor thresholds for cooling or heating by setting Installer Setup Numbers (IS) 6 and 7 to desired values.

Remote Temperature Sensor Wiring
The TR21 is an optional remote temperature sensor that can be used as an alternative to the internal sensor. In addition to the TR21, other sensors that use a 20k Ohm curve may be used as the remote sensor.

WARNING: Risk of electrical shock. Can cause severe injury, property damage or death.
Disconnect power supply before servicing.

CAUTION: Erratic system operation hazard. Failure to follow proper wiring practices can introduce disruptive electrical interference (noise).

Keep wiring at least one foot away from large inductive loads such as motors line starters, lighting ballasts, and large power distribution panels. Shielded cable is required in installations where these guidelines cannot be met. Ground shield only to grounded controller case.

IMPORTANT
All wiring must comply with local electrical codes and ordinances or as specified on installation wiring diagrams.

• Wall module wiring can be sized from 16 to 22 AWG (1.31 to 0.33 sq. mm) depending on the application.
• The maximum length of wire from the thermostat to a wall module is 1000 ft. (305 m).
• Twisted pair wire is recommended for wire runs longer than 100 ft. (30.5 m).

1. Check Installer Setup Number (IS) 4 to ensure it is set to use the remote sensor. (See Table 4 ).
2. Wire sensor to Rs and Sc thermostat terminals.
3. Push excess wire back into the hole. Plug the hole using non-hardening caulk, putty or insulation to prevent drafts from affecting performance.
4. Remove sensor cover.
5. Mount sensor to the wall or junction box using the screws and anchors provided.
6. Level the sensor for appearance only. Device functions correctly even when not level.
7. Replace sensor cover.

NOTE: For complete wiring instructions, please follow the installation instructions provided with the remote sensor.

Sensor Wiring for Temperature Averaging
Fig. 4–Fig. 6 illustrate sensor wiring for temperature averaging applications.

Thermostat Wiring Diagrams

The figures in this section illustrate typical wiring for:

• TB6575A1016,TB6575B1000 and TB6575C1016 fan coil thermostats, which are 120/240/277 Vac powered.
  Refer to Fig. 7–Fig. 13, beginning on page 8.
• TB8575A1016 model, which is 24 Vac powered. Refer to Fig. 14–Fig. 20 .

1. REMOVE PRE-WIRED WIRE FROM TERMINAL 5 (MID FAN SPEED).
2. JUMPER TERMINALS 5 AND 6 (MID AND HIGH FAN SPEEDS). FAN MEDIUM SETTING WILL OPERATE ON HIGH SPEED.
3. CONNECT TERMINAL 7 TO THE MID FAN SPEED WIRE FROM THE PREVIOUS SYSTEM.
4. REWIRE THE PREVIOUS MID SPEED FAN WIRE TO THE NEUTRAL CIRCUIT IN THE SYSTEM.
5. CHANGE INSTALLER SETUP IS CODE 9 TO 2 FOR 2 SPEED FAN CONTROL.

24 Vac Wiring Diagrams (TB8575)

For the TB8575A1016 model, a 24 Vac Class 2 NEMA rated transformer must be used.

1. REMOVE PRE-WIRED WIRE FROM TERMINAL 5 (MID FAN SPEED).
2. JUMPER TERMINALS 5 AND 6 (MID AND HIGH FAN SPEEDS). FAN MEDIUM SETTING WILL OPERATE ON HIGH SPEED.
3. CONNECT TERMINAL 7 TO THE MID FAN SPEED WIRE FROM PREVIOUS SYSTEM.
4. REWIRE THE PREVIOUS MID FAN SPEED WIRE TO THE NEUTRAL CIRCUIT IN THE SYSTEM.
5. POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
6. CHANGE INSTALLER SETUP IS CODE 9 TO 2 FOR 2 SPEED FAN CONTROL.

Removing the Thermostat

WARNING: Risk of electrical shock. Can cause severe injury, property damage or death.
Disconnect power supply before servicing.

CAUTION: Equipment damage hazard. Improper removal can damage the thermostat.
Carefully follow the thermostat removal directions.

If it is necessary to remove the thermostat from the subbase, refer to Fig. 21 and perform the following steps:

1. Turn off the thermostat by pressing the system button until OFF displays.
2. Remove the power source from the thermostat.
3. Remove the small safety screw at the bottom of the thermostat.
4. Use both hands to pull the thermostat straight away from the sub-base.

SETUP

The thermostat provides an LCD display, two buttons below the display for System and Fan control and two adjustment buttons (Up and Down) to the right of the display. See Fig. 23.

Settings, including setpoints, are permanently retained in EEPROM in case of a power outage.
Fig. 22 illustrates all the possible LCD display elements. Only those elements pertinent to the current settings and status (including the text for the two buttons, System and Fan), actually display.

Power-up
At power-up, the thermostat’s LCD shows all display segments for two seconds, enters a self-test mode for a few seconds, and then displays the current room temperature (default screen), as shown in Fig. 23.

NOTE: If there is a temperature sensor failure or the temperature is outside of the operating range, the room temperature display shows two dashes, — —.
When the sensor returns to its operating range, the temperature display resumes.

CAUTION: Equipment damage hazard.
Power overload will damage the thermostat.
The thermostat has a safety fuse rated at 15 A/ 250 Vac. If the fuse blows, the thermostat must be replaced. The fuse is not field replaceable.

This fuse is provided as a safety feature to prevent fire if the thermostat is overloaded.

Installer Setup (IS) Mode

To enter Installer Setup Mode:
Press and hold both the System button (labeled Heat/Cool) and the Up Arrow button for three (3) seconds.
This displays the setup screen on the LCD. See Fig. 24.

NOTE: Exiting Installer Setup Mode is the same as the method for entering setup mode.
Table 4 provides the setup codes (IS codes) and values.
To enter the setup parameters:

1. Press the System (Heat/Cool) button to cycle through the IS codes, which display in the upper right following the word Setup.
2. Press the Up or Down Arrow buttons to cycle through the option values for the currently displayed IS code. The values display in the center of the screen.
3. After the desired value displays, press the System button to store your value selection and display the next IS code.

Table 4. Installer Setup (IS) Codes and Options.

Installer Test (IT) Mode

To enter Installer Test Mode:
Press and hold both the Up arrow button and the Down Arrow button for three (3) seconds.
This displays all segments of the LCD screen on the LCD. See Fig. 22.

Table 5 provides the Test codes (IT codes) and values. To enter the IT codes:

1. Press the System (Heat/Cool) button to cycle through the IT codes, which display in the upper right above the word Test.
2. Press the Up or Down Arrow buttons to cycle through the values for the currently displayed IT code. The values display in the center of the screen.
3. After the desired value displays, press the System button to store your value selection and display the next IT code.

NOTE: Exiting Installer Test Mode is the same as the method for entering test mode,

Table 5. Installer Test (IT) Codes and Options.

OPERATION

PROPORTIONAL + INTEGRAL (P+I) CONTROL
Like a mechanical thermostat, the fan coil thermostats have On/Off control output. However, this output is regulated by a P+I algorithm, enabling the thermostat to control closer to setpoint than conventional thermostats.
This results in performance where the space temperature is maintained within 0.75°C (1.5°F) of the setpoint regardless of fan speed.

NOTE: Integral action corrects the temperature control errors of proportional-only control, but it is slower to react to large temperature or setpoint changes.

Economy Setback Modes

ACTIVITY SENSING (IS CODE #22)
If Activity Sensing is enabled, any time the thermostat is not touched (no single key is pressed) for the duration selected, the thermostat automatically falls back into the Economy Setback. The LCD displays ECONOMY SETBACK just to the right of the main temperature display to indicate Activity Sensing mode is active. When any key is pressed, the thermostat controls to Occupied mode.

BUTTON PRESS SETBACK (IS CODE #19-5)
The default remote setback option is for economy setback via a button press on the thermostat. In this mode, the thermostat can quickly be setback by pressing and holding down the System Mode button for more than 3 seconds. The LCD displays ECONOMY SETBACK just to the right of the main temperature display to indicate the Setback is active. When any key is pressed, the thermostat controls to Occupied mode.

REMOTE SETBACK (IS CODE #19)
Remote Setback is activated by a dry contact closure on the remote setback input from an occupancy sensor, time switch, or hotel card key. The thermostat controls to the user/installer defined setback setpoints for increased energy savings. The LCD displays Economy Setback just to the right of the main temperature display to indicate the Remote Setback mode is active.
When Remote Setback is active, all buttons on the thermostat are disabled. However, the button combinations to access Installer Setup (IS) and Installer Test (IT) remain enabled.

ECONOMY SETBACK OPERATION
For Heat Mode, when Economy Setback is enabled, the set point changes to the remote setback heating setpoint (IS CODE #20).
For Cool Mode, when Economy Setback is enabled, the set point changes to the remote setback cooling setpoint (IS CODE #21).

For 4 pipe applications with Auto Changeover and Heat/Cool Setpoints, when Economy Setback is enabled, the cool setpoint changes to the remote setback cooling setpoint and the heat setpoint changes to the remote setback heating setpoint. The new effective deadband is the difference between the remote setback heating setpoint and the remote setback cooling setpoint.
Fig. 26 illustrates the relationship between setpoints, Remote Setback, and deadband for auto changeover with heat and cool setpoints.

For 4 pipe applications with Auto Changeover and a single setpoint, when Economy Setback is enabled, the setpoint will revert to a dual heat/cool setpoint approach. The remote setback heating and remote setback cooling setpoints will be used to create an effective unoccupied deadband.

Fig. 27 illustrates the unoccupied deadband when Economy Setback is enabled for 4-pipe single setpoint auto changeover.

Fan Modes

VERSASPEED™ FAN RAMPING
When the fan switch is in auto, the thermostat will cycle the fan using the fan ramping algorithm. The appropriate fan speed is selected according to Fig. 28.
The fan ramping algorithm is illustrated in Fig. 28

AUTO FAN RESET (IS CODE #24)
If Auto Fan Reset is enabled, and a constant fan speed is selected, the thermostat resets the fan to Auto.

Value = 1: The fan resets back to Auto after 2 hours.
Value = 2: The fan resets back to Auto after 4 hours. The start time is calculated after the initial call for Heat/Cool is satisfied. Then, the two or four hour timing begins. The fan is set back to Auto when the 2-hour or 4-hour delay expires.

Application Modes

2 PIPE SEASONAL CHANGEOVER APPLICATIONS These applications require the pipe sensor as a N.O, N.C., or Analog Input to detect seasonal changeover:

• 2 pipes with auto changeover
• 2 pipes with auxiliary heat

Changeover occurs when the system has been changed over from the boiler to the chiller. This occurs on a seasonal basis from winter to summer months. When using a pipe sensor as an analog input, the thermostat can use the logic below to determine what mode to operate in. A changeover will occur when the pipe temperature goes above the threshold for heating or below the threshold for cooling. If a purge has not occurred or a call has not been satisfied in awhile, the pipe temperature may start to get close to the ambient temperature. In this case, the thermostat will only changeover once the temperature falls into the opposite threshold.

2 Pipes with Auto Changeover
For this application the system switch only provides “Off” and “Auto.” When in “Auto” mode the water temperature will indicate if the thermostat should operate in heating or cooling.

Operation:
After exiting the installer setup, the thermostat will perform a 5 minute purge. During this initial 5 minute purge, the valve (W/Y) will energize and the fan will be de-energized. After the 5 minute purge, the thermostat will go into the appropriate mode as described in Table 6.

Table 6. Logic for 2 Pipes with Auto Changeover 

*If pipe temperature is between the two threshold values after the 5 minute purge occurs, the thermostat will activate a second 5 minute purge to double check the water temperature. If after the second 5 minute purge, the water temperature is still between the two thresholds, the valve output will be disabled and only manual fan will be available. It will stay in this operation until the next purge cycle occurs.

2 Pipes with Auxiliary Heat
For this application, when there is hot water in the pipes, the system switch provides “Off” and “Heat.” When there is cold water in the pipes, the system switch provides
“Off,” “Heat,” and “Cool.”

Operation:
After exiting the installer setup, the thermostat will perform a 5 minute purge. During this time, the valve (W/Y) will energize and the fan and auxiliary heat (Y/A) will be de-energized. After the 5 minute purge, the thermostat will go into the appropriate mode as described by Table 7.

Table 7. Logic for 2 Pipes with Auxiliary Heat

If pipe temperature is between the two threshold values after the 5 minute purge occurs, the thermostat will activate a second 5 minute purge to double check the water temperature. If after the second 5 minute purge, the water temperature is still between the two thresholds, the valve output will be disabled and only auxiliary heat will be available for heating.
Auxiliary heat (Y/A) always de-energizes during purges.

Purge Cycles for 2 Pipe Seasonal Changeover Applications
For 2 Pipe with Auto Changeover and 2 Pipe with Auxiliary Heat applications, the thermostat will run purge cycles to determine if there is hot or cold water in the pipes.
A 5 minute purge will occur every 2 or 24 hours (IS 25) to ensure that the pipe sensor is sensing the correct mode during seasonal changeover months.
A 5 minute purge will also occur anytime the installer setup or installer test menus are exited, whenever the thermostat is switched from its “Off” position, and if the power is reset.

NOTE: For the 2 Pipe with Auxiliary Heat application, the thermostat must be in the “Off” position for more than 30 minutes before a 5 minute purge will occur when it is switched back into “Heat” or “Cool.”

4 PIPES AUTO CHANGEOVER
Single Set Point Method

In 4 pipe auto changeover with a single setpoint, the temperature is always controlled to the setpoint. Switching points are used to determine when to switch between heating and cooling modes. If the current mode is heat and the temperature drifts above the cool switch point (Setpoint + Switching Differential), the thermostat will switch to heat operation and will heat the space until setpoint is reached.
For this application, the setpoint setting and switching points are illustrated in Fig. 29. The switching differential is defined via IS code 10.

Heat/Cool Setpoint Method
In 4 pipe auto changeover with heat and cool setpoints, the system key is used to switch between the heating setpoint and cooling setpoints. Use the Up and Down arrow buttons to change the setpoint.
For this application, the setpoint settings and deadband are illustrated in Fig. 30. The deadband is changed via IS code 10.

TROUBLESHOOTING

Table 8 provides troubleshooting information.