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
N.C. 24 Vac thermal valve
(Hot wax thermal body valve)
Any gear driven end device
valve or damper actuator
Properly sized electric base
board strip
Oversized capacity electric
base board strip
Properly sized electric duct
heater
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.
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
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
energized)
•
red
Intensity is proportional to reheat
output
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.
Table 8. Knob position
Rotate Knob to: Green
Red (reheat models only)
T7984B & C
Minimum Position ON
OFF
Maximum Position OFF
ON
The night setback feature can be temporarily overridden for 2-
1/2 hours by depressing the override button on the thermostat
cover.
the action of the output.
Automation and Control Solutions
Honeywell International Inc.
1985 Douglas Drive North
Golden Valley, MN 55422
customer.honeywell.com
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario M1V 4Z9
® U.S. Registered Trademark
© 2005 Honeywell International Inc.
95C-10815–2 M.S. Rev. 09-05
