Honeywell T7984 C, T7984 B, T7984 A User Manual

T7984 A,B,C Electronic Modulating Control Thermostats
PRODUCT DATA

FEATURES

• PI (proportional and integral) control action provides
accurate, stable room temperature control.
• T7984 models are used with Series 70 direct-coupled
damper actuators such as ML7161 or ML7984, or with valve actuators such as ML7285, ML7421, VC7930 or M7410.
• All models feature user-friendly set point knob.
• All models feature output status LEDs for installer
check-out.
• Locking cover and range stops are standard.
• Night setback models feature selection of two different
offset temperatures and use central time switch control.
• Night setback models feature 2 1/2 hour local timed
override.

APPLICATION

These microprocessor-based thermostats provide proportional - integral (PI) individual room temperature control in zoned commercial Heating, Ventilating, and Air Conditioning systems such as hydronic heating and/ or cooling, pressure dependent VAV or by-pass box with or without terminal reheat.
The T7984 family provides modulating analog 2 to 10 Vdc control. Optional features include automatic heat/ cool changeover, reheat control, remote night setback with local timed override, and remote sensor on VAV models.
• Heat/cool models feature automatic changeover with
3° or 5°F (1.5°C or 3°C) selectable Zero Energy Band (Z.E.B.) to meet requirements of ASHRAE 90.1
• Heat/cool models have installer-definable setpoint at
midpoint of Z.E.B, at heating setpoint, or at cooling setpoint.
• Reheat models feature fast/slow response selection to
match heating system dynamics.
• DIP switch selectable 75°F (24°C) high limit heating
setpoint and low limit cooling setpoint.
• Horizontal and vertical covers included.
Contents
Application......................................................................... 1
Features ............................................................................ 1
Specifications .................................................................... 2
Ordering Information ......................................................... 2
Installation ......................................................................... 3
T7984A.............................................................................. 4
T7984B.............................................................................. 5
T7984C.............................................................................. 6
Checkout ........................................................................... 8
95C-10815-2
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS

SPECIFICATIONS

IMPORTANT
The specifications given in this publication do not include normal manufacturing tolerances. Therefore, this unit may not exactly match the listed specifications. Also, this product is tested and calibrated under closely controlled conditions, and some minor differences in performance can be expected if those conditions are changed.
MODELS: T7984A,B,C, 2 to 10 Vdc analog output
Table 1. Model Specifications
Cool/Heat
Changeover
Model Output 1
T7984A Modulating 2 to
10 Vdc
T7984B Modulating 2 to
10 Vdc
T7984C Modulating 2 to
10 Vdc
* Remote sensor models are: 272845 Remote wall mount sensor 272847 Remote duct mount sensor
DIMENSIONS
See Figure 1. MOUNTING: Mounts to single-gang NEMA-standard 2"x 4"
electrical box, or directly to wall requires 1 1/8“ [35„mm] access hole for wiring.
WIRING: Four to eight 1/8“ screw terminals suitable for 2 no.
18 AWG [1 mm 2] wires each depending on model.
POWER SUPPLY: 19-30 Vac, 50-60 Hz, 2 VA, Class 2. (Does
not include actuator or reheat stage power requirements.)
OPERATING AMBIENT:
32-104°F [0-40°C] at 5-95% Relative Humidity (non-
condensing).
ACCURACY: 1°F (0.6°C) PRECISION: ±1°F (0.5°C) tempera-
ture after stabilization.
PRECISION: ±1°F (0.5°C) temperature after stabilization. SETPOINT RANGE: 55-90°F [13-32°C], T7984A. Heating: 55-75°F [13-24°C], T7984B, C*. Cooling: 75-90°F [24-32°C], T7984B, C*.
For Output 1 Output 2 Night Setback
Dry Contact or Sensor
- - Dry Contact Internal or
Dry Contact or Sensor
On/off - Internal or
Modulating 2 to 10 Vdc
Main
Temperature
Sensor *
remote
remote
Dry Contact Internal or
remote
* The maximum heating setpoint and minimum cooling
setpoint is electronically limited to 75°F [24°C].
REMOTE SENSOR: 47 k NTC thermistor [part nos. 272845
and 272847].
ANALOG OUTPUT: 2 to 10 Vdc, 2 mA max. SWITCHED OUTPUT RATING: 0.5A running, 1.1A inrush,
24Vac, protected with selfresetting fuse.
OPERATING PARAMETERS:
APPROVALS:
Designed for Class II low voltage installation only. Case and cover meets UL„94-5V flammability requirements,
and North American codes for line voltage thermostat enclosures.
Meets requirements of F.C.C. Part 15 Class B, IEC 801-3 for
radio frequency interference.
ACCESSORIES:
272845 - Remote sensor (wall mounted). 272846 - Adaptor plate for 2-gang NEMA, or British 75 mm
electrical box.
272847 - Remote sensor (duct mounted).
See Table 2 for installer selections.
Mode Selection
Input
-
Jumper
-
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.
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 Honeywell Automation and Control Products Sales Office (check white pages of your phone directory).
2. Honeywell Customer Care
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.
95C-10815–2 2
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS
OUTPUT 2 ON/OFF CPH
T7984B only
For more information, see on/off output cycle per hour application note.
CYCLES/HOUR S1
FAST 8 CPH 1 SLOW 4 CPH 0
It is possible to fix the number of times per hour the on/off output will be energized.
ZERO ENERGY BAND T7984B & C only
ZEB S2
5°F (3°C) 1
3°F (1.5°C)
0
On models which have 2 outputs, 1 for cooling and 1 for heating, it is possible to adjust the zero energy band value (dead band between heating and cooling endpoints).
SETPOINT DIAL DEFINITION
T7984B & C only
For more information, see setpoint dial definition & setpoint limitation application note.
Models with cooling and heating outputs
» Setpoint dial centered, 75˚F limitation not active.
» Setpoint dial defined as heating, 75˚F limitation active.
DEFINITION S3
S4
75°F OVERRIDE
1 1
HEATING DIAL 0
1
COOLING DIAL
1 0
CENTERED HC
0 0
» Setpoint dial defined as cooling, 75˚F limitation active.
» Setpoint dial centered, 75˚F limitation active.
DAY/NIGHT SETBACK
T7984B & C only
HEAT SETBACK COOL SETUP
S5
10°F (5°C)
20°F (10°C)
1
5°F (3°C)
5°F (3°C)
0
Night mode setpoints can be adjusted to different values depending on the application.
REMOTE SENSOR T7984A, B & C
On model T7984A, switch S7 & S8 are not used.
MAIN SENSOR LOCAL INTERNAL REMOTE SENSOR
For duct return air or remote room sensor control only.
1
S6
Do not use remote sensor in supply or discharge air
0
control applications.
ON = 1
OFF = 0 1 2 3 4 5 6
Table 2. Option Settings
T7984 Model
Parameter Selection
Reheat Time Constant
Zero Energy
Fast (7.5 min.); or Normal (15 min.)
3°F (1.5°C); or 5°F (3°C)
A B C
Band Setpoint
Definition Night
Setback
Heating; Cooling or H/C midpoint
5°F (3°C) heat/cool offset, or 10°F (5°C) setback / cooling
shutdown
Main Sensor Remote or internal
CAUTION
Disconnect power supply to prevent electrical shock or equipment damage.
Wiring
Typical wiring connections are shown in Fig.2 to Fig.7. Wiring connections may be made to the screw terminal block with 2­18AWG or 1-14AWG, solid or stranded copper wires. Connect the system wires to the thermostat terminals. Push excess wire back into hole. Plug hole to prevent drafts.
Auxiliary screw terminal strip may be used in a junction box when the application requires multiple wires to be brought down at the thermostat. This can make troubleshooting, startup and servicing easier.
DIP Switch Settings
T7984 thermostats must be configured for proper operation by setting DIP switches.
T7984B Reheat output control action: 7.5 or 15 minutes.
T7984B,C Zero energy band (ZEB): 3°F (2°C) or 5°F (3°C) Setpoint adjustment: cooling,centred, heating centred with limit override for commissioning. Night setback amount: see Table 2 for complete listing of option settings.
Fig. 1. Dimensions in inches (mm)

INSTALLATION

Location

Install the thermostat about 5 ft. (1.5 m) above the floor in an area with good air circulation at average temperature conditions.
Do not install thermostat where it may be affected by:
• drafts, or dead air spots behind doors and in corners.
• hot or cold air from ducts.
• radiant heat from sun or appliances.
• concealed pipes and chimneys.
• unheated (cooled) areas such as an outside wall behind the
Mounting
The thermostat can be mounted directly on the wall with or without a wallplate or a standard single gang electrical box, or double gang with adaptor plate (accessory part 272846).
thermostat.
T7984A,B,C Main sensor, internal or remote.
Table 3. T7984 DIP Switch Definition
3 95C-10815–2
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS

T7984A

Output 1 analog
2œ10V
Cooling and/or
Output 2
on/off
Mode input
jumper
Changeover input
for Out 1
X X
Day/Night
mode (NSB)
Remote sensor
option
heating

WIRING

To install a remote duct or room temperature sensor, adust DIP the screw terminals and wire as shown. switch S6 to 0 = off and wire as shown.
To reverse operation of output 1 to heating, install the thermostat.) changeover contact or the changeover sensor across
Duct
or
Room
Remote sensor input
(0 Vac)
Not used
Output 1
2-10 Vdc
Changeover
input for Out 1
24 Vac
Power supply (0 Vac)
(If sensor is used, wire 1changeover sensor per
Changeover
contact
2-10 Vdc valve or VAV analog actuator
Input (2-10 Vdc) 24 Vac Common
Changeover
OR
sensor
24 Vac Transformer
75°F setpoint
limit

SEQUENCE

Opened
100%
50%
Closed
0%
Heating mode changeover input active
Temperature increase

DIP SWITCH SETTINGS

Fig. 2. T7984A Wiring
SETPOINT DIAL CENTERED
End
Device Device
opened opened
10 Vdc 10 Vdc
End
Device
closed
OUTPUT 1 ANALOG
End
End Device closed
Fig. 3. T7984A Sequence
REMOTE SENSOR
MAIN SENSOR S6
LOCAL INTERNAL
REMOTE SENSOR
1 0
Cooling mode
ON = 1
OFF = 0
<< Not used
6 7 8
Fig. 4. T7984A Dip Switch Settings
95C-10815–2 4

T7984B

T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS
Output 1 analog
2œ10V
Cooling Heating Heating Cooling
Output 2
on/off
Mode input
jumper
Mode A (Jumper out)
Mode B (Jumper in)
Changeover input
for Out 1
Day/Night
mode (NSB)
Remote sensor
option
X X X
75°F setpoint
limit

WIRING

To install a remote duct or room temperature sensor, adjust * To enable mode B of operation, install a jumper across the DIP switch S6 to 0 = off and wire as shown. screw terminals and wire as shown
Duct
or
Room
NSB contact
from a central timer
Remote sensor input
(0 Vac)
NSB input
Output 2
On/off
Output 1
2-10 Vdc
Mode input
24 Vac
Power supply (0 Vac)
2-10 Vdc valve or VAV analog actuator
Input (2-10 Vdc) 24 Vac Common
24 Vac Transformer
24 Vac on/off relay or valve
R
Fig. 5. T7984B Wiring

SEQUENCE

Mode A (jumper not installed)
Output 1 analog in cooling mode
Output 2 on/off in heating mode
HEATING
SETPOINT
100%
End
Device
on
SETPOINT DIAL DEFINITION
SETPOINT
CENTERED
IN ZERO
ENERGY BAND
COOLING
SETPOINT
End Device opened 10 Vdc
Mode B (jumper installed)
Output 1 analog in heating mode
Output 2 on/off in cooling mode
HEATING
End
SETPOINT
100%
Device opened 10 Vdc
SETPOINT DIAL DEFINITION
SETPOINT
CENTERED
IN ZERO
ENERGY BAND
COOLING
SETPOINT
End
Device
on
50%
Device
0%
OUTPUT 2
ON/OFF
off
ZERO ENERGY BAND
Temperature increase
Fig. 6. T7984B Sequence (Mode A)

DIP SWITCH SETTINGS

SETPOINT DIAL DEFINITION
DEFINITION S3
75°F OVERRIDE
HEATING DIAL 0 COOLING DIAL
CENTERED HC
OUTPUT 2 ON/OFF CPH
CYCLES/HOUR S1
FAST 8 CPH 1 SLOW 4 CPH 0
ZERO ENERGY BAND
3°F (1.5°C)
ZEB S2
5°F (3°C)
50%
Device closed
2 Vdc
OUTPUT 1
ANALOG
S4
1 1
1 1 0 0 0
1 0
ON = 1
OFF = 0
123 4 56
Fig. 8. T7984B Dip Switch Settings
0%
Device closed
2 Vdc
OUTPUT 1
ANALOG
ZERO ENERGY BAND
Temperature increase
Fig. 7. T7984B Sequence (Mode B)
DAY/NIGHT SETBACK
HEAT SETBACK
10°F (5°C)
5°F (3°C)
REMOTE SENSOR
MAIN SENSOR S6 LOCAL INTERNAL 1 REMOTE SENSOR
COOL SETUP
20°F (10°C)
5°F (3°C)
0
S5
1 0
Device
off
OUTPUT 2
ON/OFF
5 95C-10815–2
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS

T7984C

Output 1 analog
2œ10V
Cooling and
Output 2
analog 2œ10V
Mode input
jumper
Changeover input
for Out 1
Day/Night
mode (NSB)
Remote sensor
option
Heating only X X X X
Heating

WIRING

To install a remote duct or room temperature sensor, adust DIP the screw terminals and wire as shown. switch S6 to 0 = off and wire as shown.
To reverse operation of output 1 to heating, install the thermostat.) changeover contact or the changeover sensor across
Duct
or
Room
NSB contact
from a central timer
Remote sensor input
(0 Vac)
NSB input
Output 2
2-10 Vdc
Output 1
2-10 Vdc
Changeover
input for Out 1
24 Vac
Power supply (0 Vac)
Fig. 9. T7984C Wiring
(If sensor is used, wire 1changeover sensor per
Changeover
contact
2-10 Vdc valve or VAV analog actuator
Input (2-10 Vdc) 24 Vac Common
Changeover
OR
24 Vac Transformer
sensor
75°F setpoint
limit
Input (2-10 Vdc) 24 Vac Common

SEQUENCE

SETPOINT DIAL DEFINITION
HEATING
SETPOINT
End
100%
50%
0%
Device
opened
10 Vdc
OUTPUT 2
ANALOG
End Device closed
2 Vdc
ZERO ENERGY BAND
Temperature increase

DIP SWITCH SETTING

75°F OVERRIDE
SETPOINT
CENTERED
IN ZERO
ENERGY BAND
End Device closed
2 Vdc
SETPOINT DIAL DEFINITION
DEFINITION S3
HEATING DIAL 0 COOLING DIAL
CENTERED HC
ZERO ENERGY BAND
ZEB S2
5°F (3°C) 1
3°F (1.5°C)
1 1
1 0
0 0
COOLING
SETPOINT
OUTPUT 1
ANALOG
End Device opened 10 Vdc
Fig. 10. T7984C Sequence
S4
1
0
ON = 1
2 3 4 56
OFF = 0
100%
50%
0%
HEATING
SETPOINT
End Device opened 10 Vdc
OUTPUT 2
ANALOG
DAY/NIGHT SETBACK
HEAT SETBACK
10°F (5°C)
5°F (3°C)
REMOTE SENSOR
MAIN SENSOR S6 LOCAL INTERNAL 1 REMOTE SENSOR
SETPOINT DIAL DEFINITION
SETPOINT
CENTERED
End Device opened 10 Vdc
Device closed
COOL SETUP 20°F (10°C)
5°F (3°C)
0
IN ZERO
ENERGY BAND
End
2 Vdc
OUTPUT 1
ANALOG
ZERO ENERGY BAND
Temperature increase
S5
1
0
End Device closed
2 Vdc
COOLING SETPOINT
Fig. 11. T7984C Dip Switch Setting
95C-10815–2 6
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS

Output 1, Modulating Analog Output 2 to 10Vdc (T7984 All)

Main output of the thermostat. On the T7984 series that output is modulating PI analog (2 to 10 Vdc). That signal uses a variable Vdc signal for the control of analog damper actuator and analog valve actuator. This type of output on the T7984 series uses a half wave rectifier bridge.
There is a status LED mounted internally that indicates the action of the output. The green LED intensity is proportional to the action of the output.

Mode Input (T7984B only)

Model T7984B has a mode input. This thermostat is designed to operate and function in 2 distinct mode of operation depending on the application requirements.
This input is not a changeover input for output 1.
Installing a jumper on the mode input will reverse modulating output 1 to operate as a heating only output & the on/off output 2 as a cooling only output. (See the control sequence section for each thermostat.)

Heat/Cool Changover of Output 1 (T7984A & C)

Models T7984A & C all have the possibility of changeover for output 1. Automatic changeover is used on systems were a valve or a VAV unit may have cold and hot water or air in the same system depending on the season. Basically output 1 is primarily cooling (Direct Acting) when the changeover input is not activated. Activating the changeover input reverses the function of output 1 to heating mode (Reverse Acting) so that the thermostat can use the end device as a heating device instead of a cooling device.

Zero Energy Band (T7984B & C)

Thermostats which have cooling and heating outputs (T7984B & C) have 2 distinct setpoints, one for heating the other for cooling (see the control curves section for each model). When the room temperature is between these to setpoints both heating and cooling outputs are off and the room temperature is in the Zero Energy Band. When the room temperature drops below the heating setpoint, output 2 output will energize. When the room temperature rises above the cooling setpoint, output 1 will energize.
Two settings values are available for Zero Energy Band: 3°F(1.5°C) or 5°F(3°C) , can be adjusted with dip switch (S2).

Setpoint Dial Definition (T7984 B & C)

Because these thermostats have 2 distinct setpoints; one for heating the other for cooling, the thermostat setpoint dial knob need to be defined as being either:
• The true heating setpoint
• The true cooling setpoint
• Or centered in the middle of the Zero Energy Band.
This can be adjusted with dip switch (S3 & S4). (See the control curves section for each model.)
75°F (25°C) Setpoint Limitation (T7984B & C)
Models with a reheat output have setpoint limitation capability compatible with ASHRAE 90.1. Both heating and cooling setpoints are internally limited to 75°F (24°C). The cooling setpoint cannot go below 75°F while the heating setpoint cannot go above 75°F. This setpoint limit can be overridden for system checkout by setting the DIP switches S3=1 and S4=1.
A common contact may be used for multiple thermostats.
For the T7984 series a single, common dry contact or 1 supply sensor per thermostat can be used for changeover. A common contact may be used for multiple thermostats.
If a supply sensor is used, changeover temperature trip point from cooling to heating is as follows:
Output 1 Heating mode
Output 1 Cooling mode
Fig. 12. Changeover temperature trip point.
(25°C) (26°C)
Supply
75°F 78°F
Temp
M24003

Main Temperature Remote Sensor (T7984A, B, C)

All thermostats have their internal sensing device (Thermistor) mounted internally in the thermostat. On the T7984A, B & C models, it is possible to install a remote room or remote duct return sensor at a different location than the thermostat.
See wiring diagram for each model on how to wire the sensor.
The remote sensor are not to be used for supply control applications.

NSB Day/Night Mode (T7984B & C)

An energy saving mode by which the actual setpoints are modified to different value than the ones adjusted on the dial.
The cooling setpoint will go up and the heating setpoint will go down. This mode is energized with a dry contact from a remote time clock.
Table 4. DIP switch setup and setback values
Two different setup & setback value can be adjusted with a DIP switch.
S5 = 1 10°F (6°C) heating 20°F (12°C) cooling setpoint
setpoint setback setup (equivalent to cooling
shut down)
S5 = 0 5°F (3°C) heating 5°F (3°C) cooling setpoint
setpoint setback setup
The system LED on the thermostat cover on these models will flash to indicate that the thermostat is in night mode. The night mode can be overridden for 2.5 hours for each thermostat individually by pressing the button switch on the thermostat cover. This will bring back the thermostat to the day mode setpoints.
A common NSB timer contact may be used for multiple thermostats.
7 95C-10815–2
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS

Output 2 On/Off (T7984B only)

A 24 Vac on/off output which is normally used to control terminal reheat in a zoned system. Example: electric base board relay, electric duct heater relay, perimeter on/off 24 Vac valve, etc.
This output can also be used for cooling applications with the mode jumper installed (See the control curves for T7984B) There is a status LED mounted internally that indicates the action of the output. The red LED indicates that the output electronic contact (triac) is energized.
This electronic contact (triac) is rated at 1.1A max. in rush and
0.5A running. This electronic contact (triac) is protected with a PTC self-resetting fuse. In the event of an overload or a short circuit, the PTC self-resetting fuse will reduce the load to a very low level. If the power is removed or the overload or the short disappears, the PTC fuse will return to its normal state and allow normal operation.
CPH (Cycles per Hour)
It is possible to fix the number of time per hour the reheat end device will be energized. Those settings are adjusted with DIP switch (S1). Two different settings are possible: 4 cycles per hour or 8 cycles per hour
Use the following setting for the following reheat device applications:
Table 5. Cycle settings for reheat device applications
4 cycles per hour 8 cycles per hour
Anything using a gas fired or oil fired terminal reheat device
Any gear driven end device valve or damper actuator
Properly sized electric base board strip
Properly sized electric duct heater
N.C. 24 Vac thermal valve (Hot wax thermal body valve)
Oversized capacity electric base board strip
Oversized capacity electric duct heater

Output 2, Modulating Analog Output 2 to 10Vdc (T7984C only)

A modulating signal that uses a variable Vdc signal for the control of analog valve actuator or SCR power controller which is normally used to control terminal reheat in a zone system.

CHECKOUT

Service LED

All thermostats have internal service LED & a system status Led on the cover. The internal service LED are colored lights that can be viewed from the side of the thermostat they are energized and the system status LED is the one mounted on the cover. (See the checkout & start up procedures section.)
Table 6. System Status LEDs
Thermostat operation can be confirmed with the System status LED on the thermostat cover.
Model Color Explanation
T7984A green High intensity = Demand for cooling or
heat. Low = no demand.
T7984B,C red Flashing = Night setback/set-up
activated.
Table 7. Internal Service LEDs
A B C Color Indication when
green Intensity is proportional to output 1
red On/off output 2 is closed (load
red Intensity is proportional to reheat

Test Condition:

1. No contact changeover input and changeover sensor
disconnected. No wire on mode input.
2. T7984B & C: set DIP switch S3 and S4 to —ON“ position
to remove 75°F (24°C) limitation.
3. Room termperatures must be between 60-80°F.
Rotate Knob to: Green
Minimum Position ON OFF Maximum Position OFF ON
energized)
output
Table 8. Knob position
Red (reheat models only)
T7984B & C
This type of output on the T7984C uses a half wave rectifier bridge. If the same transformer is to be used for the thermostat and the end device, be sure to select end devices which also use a half wave rectifier bridge.
There is a status LED mounted internally that indicates the action of the output. The red LED intensity is proportional to the action of the output.
Automation and Control Solutions
Honeywell International Inc. 1985 Douglas Drive North Golden Valley, MN 55422 customer.honeywell.com
® U.S. Registered Trademark © 2005 Honeywell International Inc. 95C-10815–2 M.S. Rev. 09-05
Honeywell Limited-Honeywell Limitée 35 Dynamic Drive Scarborough, Ontario M1V 4Z9
The night setback feature can be temporarily overridden for 2­1/2 hours by depressing the override button on the thermostat cover.
Loading...