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
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-
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.
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