Honeywell T7984 B Thermostat User Manual

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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.  
ꢀꢀ Heat/cool models feature automatic changeover with  
APPLICATION  
3
° or 5°F (1.5°C or 3°C) selectable Zero Energy Band  
Z.E.B.) to meet requirements of ASHRAE 90.1  
(
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.  
ꢀꢀ 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.  
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.  
ꢀꢀ Horizontal and vertical covers included.  
Contents  
Application......................................................................... 1ꢀꢀ  
Features ............................................................................ 1ꢀꢀ  
Specifications .................................................................... 2ꢀꢀ  
Ordering Information ......................................................... 2ꢀꢀ  
Installation ......................................................................... 3ꢀꢀ  
T7984A.............................................................................. 4ꢀꢀ  
T7984B.............................................................................. 5ꢀꢀ  
T7984C.............................................................................. 6ꢀꢀ  
Checkout ........................................................................... 8ꢀꢀ  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
SPECIFICATIONS  
IMPORTANTꢀ  
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  
For Output 1  
Main  
Temperature ModeSelection  
Sensor *  
Model  
T7984A  
Output 1  
Output 2  
On/off  
Night Setback  
Input  
Modulating 2 to Dry Contact or  
-
Internal or  
-
1
0 Vdc  
Modulating 2 to  
0 Vdc  
Modulating 2 to Dry Contact or  
0 Vdc Sensor  
Sensor  
remote  
T7984B  
T7984C  
-
-
Dry Contact  
Internal or  
remote  
Jumper  
-
1
Modulating 2 to Dry Contact  
10 Vdc  
Internal or  
remote  
1
*
2
2
Remote sensor models are:  
72845 Remote wall mount sensor  
72847 Remote duct mount sensor  
DIMENSIONS  
See Figure 1.  
* The maximum heating setpoint and minimum cooling  
setpoint is electronically limited to 75°F [24°C].  
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.  
REMOTE SENSOR: 47 kNTC thermistor [part nos. 272845  
and 272847].  
ANALOG OUTPUT: 2 to 10 Vdc, 2 mA max.  
WIRING: Four to eight 1/8“ screw terminals suitable for 2 no.  
1
8 AWG [1 mm 2] wires each depending on model.  
SWITCHED OUTPUT RATING: 0.5A running, 1.1A inrush,  
24Vac, protected with selfresetting fuse.  
POWER SUPPLY: 19-30 Vac, 50-60 Hz, 2 VA, Class 2. (Does  
not include actuator or reheat stage power requirements.)  
OPERATING PARAMETERS: See Table 2 for installer selections.  
OPERATING AMBIENT:  
APPROVALS:  
3
2-104°F [0-40°C] at 5-95% Relative Humidity (non-  
condensing).  
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.  
ACCURACY: 1°F (0.6°C) PRECISION: ±1°F (0.5°C) tempera-  
ture after stabilization.  
Meets requirements of F.C.C. Part 15 Class B, IEC 801-3 for  
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*.  
radio frequency interference.  
ACCESSORIES:  
2
2
72845 - Remote sensor (wall mounted).  
72846 - Adaptor plate for 2-gang NEMA, or British 75 mm  
electrical box.  
Cooling: 75-90°F [24-32°C], T7984B, C*.  
272847 - Remote sensor (duct mounted).  
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 Careꢀꢀ  
1
885 Douglas Drive Northꢀꢀ  
Minneapolis, Minnesota 55422-4386ꢀꢀ  
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.ꢀꢀ  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
Table 2. Option Settings  
Selection  
CAUTION  
T7984 Model  
Disconnect power supply to prevent electrical  
shock or equipment damage.  
Parameter  
A
B
C
Reheat Time Fast (7.5 min.); or Normal  
Constant (15 min.)  
Wiring  
Typical wiring connections are shown in Fig.2 to Fig.7. Wiring  
connections may be made to the screw terminal block with 2-  
8AWG 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.  
Zero Energy 3°F (1.5°C); or 5°F (3°C)  
Band  
1
Setpoint  
Definition  
Heating; Cooling or H/C  
midpoint  
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.  
Night  
Setback  
5°F (3°C) heat/cool offset, or  
10°F (5°C) setback / cooling  
shutdown  
Main Sensor Remote or internal  
DIP Switch Settings  
T7984 thermostats must be configured for proper operation byꢀꢀ  
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.ꢀꢀ  
T7984A,B,C ꢀ  
Main sensor, internal or remote.ꢀꢀ  
Table 3. T7984 DIP Switch Definition  
OUTPUT 2 ON/OFF CPH  
T7984B only  
For more information, see on/off output cycle per hour application note.  
CYCLES/HOUR  
FAST 8 CPH  
SLOW 4 CPH  
S1  
1
0
It is possible to fix the number of times per hour the on/off  
output will be energized.  
ZERO ENERGY BAND  
ZEB  
T7984B & C only  
S2  
1
0
On models which have 2 outputs, 1 for cooling and 1 for  
heating, it is possible to adjust the zero energy band value  
5
°F (3°C)  
(
dead band between heating and cooling endpoints).  
3
°F (1.5°C)  
Fig. 1. Dimensions in inches (mm)  
SETPOINT DIAL DEFINITION  
For more information, see setpoint dial definition & setpoint limitation application note.  
T7984B & C only  
DEFINITION  
5°F OVERRIDE  
HEATING DIAL  
COOLING DIAL  
CENTERED HC  
S3  
1
0
1
0
S4  
1
1
0
0
Models with cooling and heating outputs  
7
»
»
Setpoint dial centered, 75˚F limitation not active.  
Setpoint dial defined as heating, 75˚F limitation active.  
INSTALLATION  
»
»
Setpoint dial defined as cooling, 75˚F limitation active.  
Setpoint dial centered, 75˚F limitation active.  
DAY/NIGHT SETBACK  
T7984B & C only  
Location  
Night mode setpoints can be adjusted  
S5  
1
0
HEAT SETBACK  
10°F (5°C)  
COOL SETUP  
20°F (10°C)  
5°F (3°C)  
Install the thermostat about 5 ft. (1.5 m) above the floor in an  
area with good air circulation at average temperature  
conditions.  
to different values depending on the  
application.  
5
°F (3°C)  
REMOTE SENSOR  
On model T7984A, switch S7 & S8 are not used.  
T7984A, B & C  
MAIN SENSOR  
LOCAL INTERNAL  
REMOTE SENSOR  
S6  
1
0
For duct return air or remote room sensor control only.  
Do not use remote sensor in supply or discharge air  
control applications.  
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  
ON = 1  
OFF = 0 1 2 3 4 5 6  
thermostat.  
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).  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
T7984A  
Output 1 analog  
œ10V  
Output 2  
on/off  
Mode input  
jumper  
Changeoverinput  
for Out 1  
Day/Night  
mode (NSB)  
Remote sensor 75°F setpoint  
option limit  
2
Cooling and/or  
heating  
X
X
WIRING  
To install a remote duct or room temperature sensor, adust DIP  
switch S6 to 0 = off and wire as shown.  
the screw terminals and wire as shown.  
(If sensor is used, wire 1changeover sensor per  
thermostat.)  
To reverse operation of output 1 to heating, install the  
changeover contact or the changeover sensor across  
Changeover  
contact  
Changeover  
sensor  
OR  
Duct  
or  
Room  
Output 1  
2-10 Vdc valve or VAV  
analog actuator  
2
-10 Vdc  
Remote  
sensor input  
Input (2-10 Vdc)  
Changeover  
input for Out 1  
2
4 Vac  
Common  
(
0 Vac)  
24 Vac  
Power supply  
24 Vac Transformer  
Not used  
(
0 Vac)  
Fig. 2. T7984A Wiring  
SEQUENCEꢀꢀ  
SETPOINT DIAL CENTERED  
End  
Heating mode  
changeover  
input active  
End  
Opened  
00%  
Cooling mode  
Device  
opened  
Device  
opened  
10 Vdc  
1
1
0 Vdc  
5
0%  
Closed  
End  
Device  
closed  
End  
Device  
closed  
0
%
OUTPUT 1 ANALOG  
Temperature increase  
Fig. 3. T7984A Sequence  
DIP SWITCH SETTINGS  
REMOTE SENSOR  
MAIN SENSOR  
LOCAL INTERNAL  
REMOTE SENSOR  
S6  
1
0
<
< Not used  
ON = 1  
OFF = 0  
6 7 8  
Fig. 4. T7984A Dip Switch Settings  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
T7984B  
Output 1 analog  
Output 2  
on/off  
Mode input  
jumper  
Changeoverinput  
for Out 1  
Day/Night  
mode (NSB)  
Remote sensor 75°F setpoint  
option limit  
2
œ10V  
Cooling  
Heating  
Heating  
Cooling  
Mode A (Jumper out)  
X
X
X
Mode B (Jumper in)  
WIRING  
To install a remote duct or room temperature sensor, adjust  
DIP switch S6 to 0 = off and wire as shown.  
* To enable mode B of operation, install a jumper across the  
screw terminals and wire as shown  
Duct  
Output 2  
2
4 Vac on/off  
or  
On/off  
relay or valve  
2
-10 Vdc valve or VAV  
Room  
Output 1  
analog actuator  
2
-10 Vdc  
Remote  
sensor input  
Mode input  
Input (2-10 Vdc)  
R
2
4 Vac  
Common  
(
0 Vac)  
24 Vac  
NSB contact  
from a central timer  
Power supply  
NSB input  
24 Vac Transformer  
(
0 Vac)  
Fig. 5. T7984B Wiring  
SEQUENCE  
Mode A (jumper not installed)  
Output 1 analog in cooling mode  
Output 2 on/off in heating mode  
Mode B (jumper installed)  
Output 1 analog in heating mode  
Output 2 on/off in cooling mode  
SETPOINT DIAL DEFINITION  
SETPOINT DIAL DEFINITION  
COOLING  
SETPOINT  
HEATING  
SETPOINT  
COOLING  
SETPOINT  
HEATING  
SETPOINT  
End  
End  
Device  
on  
SETPOINT  
CENTERED  
IN ZERO  
SETPOINT  
CENTERED  
IN ZERO  
Device  
opened  
10 Vdc  
End  
End  
Device  
on  
Device  
opened  
100%  
1
00%  
ENERGY BAND  
ENERGY BAND  
1
0 Vdc  
5
0%  
0%  
5
0%  
Device  
closed  
Device  
closed  
2 Vdc  
Device  
off  
Device  
off  
2
Vdc  
0
%
OUTPUT 1  
ANALOG  
OUTPUT 2  
ON/OFF  
OUTPUT 2  
ON/OFF  
OUTPUT 1  
ANALOG  
ZERO ENERGY BAND  
Temperature increase  
ZERO ENERGY BAND  
Temperature increase  
Fig. 6. T7984B Sequence (Mode A)  
Fig. 7. T7984B Sequence (Mode B)  
DIP SWITCH SETTINGS  
SETPOINT DIAL DEFINITION  
DEFINITION  
5°F OVERRIDE  
S3  
1
S4  
1
7
DAY/NIGHT SETBACK  
HEATING DIAL  
COOLING DIAL  
CENTERED HC  
0
1
0
1
0
0
HEAT SETBACK  
10°F (5°C)  
5°F (3°C)  
COOL SETUP  
20°F (10°C)  
5°F (3°C)  
S5  
1
0
OUTPUT 2 ON/OFF CPH  
CYCLES/HOUR  
FAST 8 CPH  
SLOW 4 CPH  
S1  
1
0
REMOTE SENSOR  
MAIN SENSOR  
LOCAL INTERNAL  
REMOTE SENSOR  
ZERO ENERGY BAND  
ZEB  
S6  
1
0
S2  
1
0
ON = 1  
5
°F (3°C)  
3
°F (1.5°C)  
OFF = 0  
1
2 3 4 5 6  
Fig. 8. T7984B Dip Switch Settings  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
T7984C  
Output 1 analog  
œ10V  
Output 2  
analog 2œ10V  
Mode input  
jumper  
Changeoverinput  
for Out 1  
Day/Night  
mode (NSB)  
Remote sensor 75°F setpoint  
option limit  
2
Cooling and  
Heating  
Heating only  
X
X
X
X
WIRING  
To install a remote duct or room temperature sensor, adust DIP  
switch S6 to 0 = off and wire as shown.  
the screw terminals and wire as shown.  
(If sensor is used, wire 1changeover sensor per  
thermostat.)  
To reverse operation of output 1 to heating, install the  
changeover contact or the changeover sensor across  
Changeover  
contact  
Changeover  
sensor  
OR  
Duct  
or  
Output 2  
2
-10 Vdc  
Room  
Output 1  
2-10 Vdc valve or VAV  
analog actuator  
2
-10 Vdc  
Remote  
Input (2-10 Vdc)  
Changeover  
Input (2-10 Vdc)  
24 Vac  
Common  
sensor input  
2
4 Vac  
input for Out 1  
Common  
(
0 Vac)  
24 Vac  
NSB contact  
from a central timer  
Power supply  
24 Vac Transformer  
NSB input  
(
0 Vac)  
Fig. 9. T7984C Wiring  
SEQUENCE  
SETPOINT DIAL DEFINITION  
SETPOINT DIAL DEFINITION  
HEATING  
SETPOINT  
SETPOINT  
CENTERED  
IN ZERO  
COOLING  
SETPOINT  
HEATING  
SETPOINT  
CENTERED  
IN ZERO  
COOLING  
SETPOINT  
End  
SETPOINT  
End  
End  
End  
Device  
opened  
1
00%  
Device  
opened  
ENERGY BAND  
100%  
Device  
opened  
10 Vdc  
ENERGY BAND  
Device  
opened  
1
0 Vdc  
1
0 Vdc  
1
0 Vdc  
5
0%  
5
0%  
End  
End  
End  
End  
Device  
closed  
2 Vdc  
Device  
closed  
2 Vdc  
Device  
closed  
Device  
closed  
2 Vdc  
2
Vdc  
0
%
0
%
OUTPUT 2  
ANALOG  
OUTPUT 2  
ANALOG  
OUTPUT 1  
ANALOG  
OUTPUT 1  
ANALOG  
ZERO ENERGY BAND  
Temperature increase  
ZERO ENERGY BAND  
Temperature increase  
Fig. 10. T7984C Sequence  
DIP SWITCH SETTING  
SETPOINT DIAL DEFINITION  
DEFINITION  
5°F OVERRIDE  
HEATING DIAL  
COOLING DIAL  
S3  
1
0
1
0
S4  
1
1
0
0
7
DAY/NIGHT SETBACK  
HEAT SETBACK  
COOL SETUP  
20°F (10°C)  
5°F (3°C)  
S5  
1
0
10°F (5°C)  
5°F (3°C)  
CENTERED HC  
ZERO ENERGY BAND  
ZEB  
S2  
1
5
°F (3°C)  
3
°F (1.5°C)  
0
REMOTE SENSOR  
MAIN SENSOR  
LOCAL INTERNAL  
REMOTE SENSOR  
S6  
1
0
ON = 1  
OFF = 0  
2 3 4 5 6  
Fig. 11. T7984C Dip Switch Setting  
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T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
Output 1, Modulating Analog Output 2 to  
Zero Energy Band (T7984B & C)  
Thermostats which have cooling and heating outputs (T7984B  
10Vdc (T7984 All)  
&
C) have 2 distinct setpoints, one for heating the other for  
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.  
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  
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.  
1
will energize.  
Two settings values are available for Zero Energy Band:  
°F(1.5°C) or 5°F(3°C) , can be adjusted with dip switch (S2).  
3
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.  
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:  
This input is not a changeover input for output 1.  
The true heating setpoint  
The true cooling setpoint  
Or centered in the middle of the Zero Energy Band.  
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.)  
This can be adjusted with dip switch (S3 & S4). (See the  
control curves section for each model.)  
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.  
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.  
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.  
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.  
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.  
If a supply sensor is used, changeover temperature trip point  
from cooling to heating is as follows:  
Table 4. DIP switch setup and setback values  
Output 1  
Heating mode  
Two different setup & setback value can be adjusted with a  
DIP switch.  
Output 1  
Cooling mode  
M24003  
S5 = 1  
10°F (6°C) heating  
setpoint setback  
20°F (12°C) cooling setpoint  
setup (equivalent to cooling  
shut down)  
(
25°C)  
(26°C)  
78°F  
Supply  
5°F  
Temp  
7
S5 = 0  
5°F (3°C) heating  
setpoint setback  
5°F (3°C) cooling setpoint  
setup  
Fig. 12. Changeover temperature trip point.  
Main Temperature Remote Sensor (T7984A, B, C)  
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.  
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.  
A common NSB timer contact may be used for multiple  
thermostats.  
The remote sensor are not to be used for supply control  
applications.  
7
95C-10815–2  
href="
T7984 A,B,C ELECTRONIC MODULATING CONTROL THERMOSTATS  
Output 2 On/Off (T7984B only)  
CHECKOUT  
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.  
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.)  
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  
Table 6. System Status LEDs  
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.  
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.  
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).  
T7984B,C red  
Flashing = Night setback/set-up  
activated.  
Two different settings are possible:  
4
cycles per hour or 8 cycles per hour  
Table 7. Internal Service LEDs  
Use the following setting for the following reheat device applications:  
A
B
C
Color  
Indication when  
green Intensity is proportional to output 1  
Table 5. Cycle settings for reheat device applications  
red  
red  
On/off output 2 is closed (load  
energized)  
4
cycles per hour  
8 cycles per hour  
Intensity is proportional to reheat  
output  
Anything using a gas fired or N.C. 24 Vac thermal valve  
oil fired terminal reheat device (Hot wax thermal body valve)  
Any gear driven end device  
valve or damper actuator  
Test Condition:  
Properly sized electric base  
board strip  
Oversized capacity electric  
base board strip  
1
.ꢀꢀ No contact changeover input and changeover sensor  
disconnected. No wire on mode input.  
Properly sized electric duct  
heater  
Oversized capacity electric  
duct heater  
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.  
Output 2, Modulating Analog Output 2 to  
Table 8. Knob position  
1
0Vdc (T7984C only)  
Red (reheat models 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.  
Rotate Knob to: Green  
Minimum Position ON  
Maximum Position OFF  
T7984B & C  
OFF  
ON  
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.  
The night setback feature can be temporarily overridden for 2-  
/2 hours by depressing the override button on the thermostat  
cover.  
1
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.  
985 Douglas Drive North  
Honeywell Limited-Honeywell Limitée  
35 Dynamic Drive  
1
Golden Valley, MN 55422  
customer.honeywell.com  
Scarborough, Ontario M1V 4Z9  
®
©
U.S. Registered Trademark  
2005 Honeywell International Inc.  
9
5C-10815–2 M.S. Rev. 09-05  

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