Honeywell T8401C User manual

® U.S. Registered Trademark
Copyright © 2002 Honeywell • • All Rights Reserved
INSTALLATION INSTRUCTIONS
69-1483-1
T8401C
Electronic Thermostats
APPLICATION
The T8401C Thermostat provides single-stage,
nonprogrammable temperature control for 24 Vac heating
cooling systems with manual changeover from heat to
cool. Heating cycle rate is selectable at 1, 3, 6, 9 or 12
cph. Cooling cycle reate is fixed at 3 cph. Temperature
indicature indication can be set for °F or °C.
The T8401C1031 (Fig. 1) is powered directly from the
zone panel. Batteries are not required because setpoints
are held permanently by non-volatile memory.
T8401C models include a thermostat, wallplate (for
wiring and mounting thermostat) and owner’s guide. See
Table 1 for a listing of thermostat features. See Table 2
for a listing of zone panels that can be used with the
T8401C.
Fig. 1. The T8401C1031 Thermostat.
MERCURY NOTICE
If this control is replacing a control that contains
mercury in a sealed tube, do not place your old
control in the trash. Dispose of properly.
Contact your local waste management authority
for instructions regarding recycling and the
proper disposal of an old control.
INSTALLATION
When Installing this Product…
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard-
ous 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, experienced service
technician.
4. After installation is complete, check out product
operation as provided in these instructions.
CAUTION
Damage to Heating/Cooling System Possible.
Be careful when handling wires during
installation. Disconnect power at furnace or main
breaker/ fuse box.
Location
Install the thermostat about 5 ft (1.5m) above the floor in
an area with good air circulation at average temperature.
See Fig. 2. Do not install the thermostat where it can be
affected by:
— drafts or dead spots behind doors and in corners.
— hot or cold air from ducts.
— radiant heat from the sun or appliances.
— concealed pipes and chimneys.
— unheated (uncooled) areas such as an outside wall
behind the thermostat.
M14752
FAN SYSTEM
Auto On Cool Off Heat
Set Room
Table 1. Thermostat Features
Model Powering Method Changeover System Selection Fan Selection
T8401C1031 Hardwired Manual Heat-Off-Cool On-Auto

T8401C ELECTRONIC THERMOSTATS
69-1483—1 2
Fig. 2. Typical location of thermostat.
This thermostat is a precision instrument and was
carefully adjusted at the factory. Handle it carefully.
Mounting Wallplate to Wall
IMPORTANT
Level only for appearance. The thermostat func-
tions normally even when not level.
Mount wallplate, T8401C, and the screws provided (see
Fig. 3) as follows:
1. Place the wallplate at the desired location on the
wall.
2. Pull the thermostat wire through the wallplate
entrance hole.
3. Select the two mounting holes that best fit the
application.
4. Fasten the wallplate to the wall using the anchors
and screws provided.
5. After wiring the wallplate, plug the hole to prevent
drafts from affecting the thermostat; see Wiring
section
.
Fig. 3. Mounting wallplate to wall.
Table 2. Zone Panel Cross Reference.
TotalZone
(TZ-3)
MABS EZ
(EZ-2, EZ-4)
Mini Zone
(MM - 2, -3) MABS II, IIL
Independent
Zone
T8401C1031 Yes Yes One Oher One Oher
Yes N o Yes No No
5 FEET
[1.5 METERS]
YES
NO
NO
NO
M11338
M12202A
WALL WALL
ANCHORS (2)
WALLPLATE
WHEN USING WALL ANCHORS, DRILL 3/16 INCH
HOLES FOR DRYWALL, 7/32 INCH HOLES FOR
PLASTER OR WOOD.
MOUNTING
SCREWS (2)
1
1

T8401C ELECTRONIC THERMOSTATS
3 69-1483—1
Setting Fan Operation (Fuel) Switch
The fan operation (fuel) switch is preset at the factory in
the F position. See Fig. 4. This is the correct setting for
most systems. If this system is an electric heat system,
set the switch to the E position. The E setting allows the
fan to turn on immediately with the heating or cooling
equipment in a system where the G terminal is
connected
.
Fig. 4. Fan operation (fuel) switch.
Wiring
IMPORTANT
Use an 18-gauge thermostat cable for proper
wiring.
All wiring must comply with local electrical codes and
ordinances. Disconnect the power supply to prevent
electrical shock or equipment damage.
NOTE: NOTE: To ensure proper mounting of thermo-
stat, restrict all wiring to the shaded area. See
Fig. 5.
The shape of the terminals permits insertion of straight or
wraparound wiring connections; either method is
acceptable. See Fig. 6.
The T8401C is powered directly from the zone panel.
Refer to Fig. 7, 8, and 9 for typical wiring hookups.
Fig. 5. Restrict wiring to shaded area.
Fig. 6. Wiring connections.
M12580
FAN OPERATION
(
FUEL
)
SWITCH
F
E
KEEP WIRING IN
SHADED AREA
MOUNTING
SCREW HOLE
MOUNTING
SCREW HOLE
WIRING ENTRANCE
HOLE
M14286
G
C
R
Y
W
B
O
TERMINAL
SCREW
M14287
G
C
R
Y
WB
O
FOR STRAIGHT INSERTION
STRIP 5/16 IN. (8 MM)
FOR WRAPAROUND
STRIP 7/16 IN. (11 MM)

T8401C ELECTRONIC THERMOSTATS
69-1483—1 4
Fig. 7. T8401 with TotalZone or MABS EZ control
panels (all zones)
.
Fig. 8. T8401 with MM-2 or MM-3 panels (zone one).
Fig. 9. T8401 with MABS II and MABS IIL control
panel (zone one).
Mounting Thermostat to Wallplate
1. Engage the tabs at the top of the thermostat and
wallplate.
2. Swing down the thermostat and press the lower
edge of the thermostat onto the wallplate to latch.
See Fig. 10.
Fig. 10. Mounting thermostat to wallplate.
Removing Thermostat from Wallplate
1. Pull the lower edge of the thermostat away from
the wall.
2. Swing the thermostat up and remove the wallplate.
M14288
W2 L G Y R W M6 M4 M1
T8401 THERMOSTAT
TOTAL ZONE MABS EZ PANEL
THERMOSTAT MOTOR
OBGYRWC
NO CONNECTION
M14289
O1 G1 B1 T6/Y T5/R T4/W M1 M4 M6
T8401 THERMOSTAT
MM-2 OR MM-3 CONTROL PANEL
NO CONNECTION
TO T8401
THERMOSTAT
(ZONE 1)
CHANGEOVER
CONTROL
DAMPER MOTOR
(ZONE 1)
OG BY RW C
M14290
O1 G1 B1 T6 T5 T4 M1 M4 M6
T8401 THERMOSTAT
MABS II OR MABS IIL CONTROL PANEL
NO CONNECTION
TO T8401
THERMOSTAT
(ZONE 1)
CHANGEOVER
CONTROL
DAMPER MOTOR
(ZONE 1)
OG BY RW C
M14292
SYSTEM
Cool Off Heat
Auto On
FAN
DASHED LINES INDICATE TABS
ON BACK OF THERMOSTAT
SYSTEM
Cool Off Heat
Auto On
FAN
ENGAGE TABS AT TOP OF THERMOSTAT
WITH SLOTS ON MOUNTING PLATE.
PRESS LOWER EDGE OF
CASE TO LATCH.
A
B
Set Room
Set Room

T8401C ELECTRONIC THERMOSTATS
5 69-1483—1
SETTINGS AND ADJUSTMENTS
Setting FAN and SYSTEM Switches
Fan and system settings are controlled manually by
using the switches located at the bottom of the
thermostat case. See Fig. 11.
Fig. 11. Digital Display and System Switches.
FAN Switch
Fan switch settings are:
On: The fan runs continuously. Use for improved air
circulation and air quality.
Auto: Normal setting for most homes. In cooling, the
fan starts and stops with the cooling equipment. In
heating, the fan is controlled directly by the heating
equipment and may start a few minutes after the
heating equipment turns on (on most systems). In
electric heat applications, the zone panel can be
configured to turn the fan on when the thermostat
calls for heat.
Slide the FAN switch in the bottom left corner of the
thermostat to select the desired fan setting.
SYSTEM Switch
System switch settings control thermostat operation as
follows:
Cool: The thermostat controls the cooling system. The
O terminal is energized.
Off: Both heating and cooling are off. O and B termi-
nals are de-engergized.
Heat: The thermostat controls the heating system.
The B terminal is energized.
Slide the SYSTEM switch in the bottom right corner of
the thermostat to select the desired system setting.
Set Temperature Setpoint
NOTE: NOTE: Temperature setpoint range is 40° to
99°F (5° to 37°C).
The temperature setpoint and the room temperature are
shown separately on the digital display. The ▼indicator
points to Set when the temperature setpoint is displayed
and to Room when the room temperature is displayed.
To set temperature setpoint:
1. Select Heat or Cool by sliding the SYSTEM switch
in the lower right corner of the thermostat to the
desired mode. See Fig. 11.
2. To display the temperature setpoint on the digital
display, press either the ▲or ▼key once. The
temperature setpoint is displayed for approximately
five seconds as the indicator points to Set and
flashes.
3. To decrease the temperature setpoint press the ▲
key. Each press changes the setpoint one degree;
press and hold to change the setpoint several
degrees.
4. To increase the temperature setpoint press the ▼
key. Each press changes the setpoint one degree;
press and hold to change the setpoint several
degrees.
Setting °F/°C Indication and Heat Cycle Rate
NOTE: NOTE: To save changes to the °F/°C indication
and the heat cycle rate, all seven steps must be
completed.
To set the °F/°C indication and heat cycle rate:
1. If the temperature is displayed in °F, set the tem-
perature setpoint to 52°F. If the room temperature
is displayed in °C, set the temperature setpoint to
11°C.
SYSTEM
Cool Off Heat
Auto On
FAN
M14293
TEMPERATURE DISPLAY
INCREASE SETTING
DECREASE SETTING
FAN SWITCH
SYSTEM SWITCH
Set Room
Set Room
INDICATOR
ROOM TEMPERATURE
SETPOINT TEMPERATURE
M14679
M14680
M14681
M14682
M14683

T8401C ELECTRONIC THERMOSTATS
69-1483—1 6
Optional System Checkout
When in steps 2 and 3 only, the ▼key can be used to
turn heat or cool outputs on and off. Change the
SYSTEM switch setting to test heat or cool outputs.
No action takes place If the SYSTEM switch is in the
Off position.
Examples: System setting at HEAT: If heat is on, the
▼key turns it off; if heat is off, ▼turns it on.
System setting at COOL: If cool is on, ▼key turns it
off; if cool is off, ▼turns it on.
2. Press the ▲▼ keys simultaneously for more than
one second to light all segments on display and to
enter installer setup mode. When the keys are
released, a two-digit software revision code is dis-
played.
NOTE: NOTE: In installer setup mode only, each press
of the ▲key momentarily displays 01. Each
press of the ▼key momentarily displays 02.
When the keys are released, these two-digit
codes are no longer displayed.
3. Press the ▲key. Factory information is displayed.
A typical example is shown, but information dis-
played varies by model. This information is for fac-
tory use only.
4. Press the ▲key again to display °C or °F.
5. Press the ▼key to change the °C or °F indication.
6. Press the ▲key to display the heat cycle rate of 1,
3, 4, 5, 6, 9, or 12. If the desired cycle rate is dis-
played, press the ▲key to exit the installer setup
mode. To change the heat cycle rate, press the ▼
key to scroll between 1, 3, 4, 5, 6, 9, and 12. Stop
scrolling when the desired cycle rate is displayed.
See Table 3 for the cycle rate options and the cor-
responding system equipment.
Table 3. Heating Cycle Rates.
a High Efficiency Furnace.
b Refer to equipment manufacturer’s instructions.
NOTE: NOTE: Steps 7 and 8 are available on select
models.
7. Press the ▲key to display cooling algorithm con-
figuration default.
8. Press the ▲key again to change cooling algorithm
to C1 or C3.
C1 = Standard cooling algorithm.
C3 = Aggressive cooling algorithm (can cause
overshooting).
9. Press the ▲key again. Current configuration (CC)
is displayed. A typical example is shown, but CC
varies by model.
10. Press the ▲key to save all changes, exit installer
setup mode and return to normal operation.
NOTE: After exiting installer setup mode, change the
setpoint to the desired room temperature.
CHECKOUT
Heating
1. Slide the SYSTEM switch to Heat and the FAN
switch to Auto.
2. Press and hold the ▲key to raise the temperature
setting several degrees above the room tempera-
ture. After approximately ten seconds, the heating
equipment should start. In conventional systems,
the system turns on the fan through the use of a
M14684
M14685
M14686
M14687
M14688
M14689
System Cycles Per Hour
Steam, Gravity 1
Hydronic Heat, Condensing
Gas
3
Furnacesa
Gas or Oil Forced Air 6
Electric Heat 9
Special Applicationsb12
M14690
M18419A

T8401C ELECTRONIC THERMOSTATS
7 69-1483—1
Cooling
NOTE: To bypass the 5 minute delay, see optional sys-
tem checkout on page 6.
CAUTION
Low Temperature Hazard.
Operating at too low of an outdoor
temperature may cause compressor damage.
Do not operate cooling if outdoor temperature is
below 50°F (10°C). Refer to equipment
manufacturer instructions.
For compressor protection, during power
interruption and on initial startup, the T8401C
Electronic Thermostat will go into a 5 minute
delay. During this delay the cooling icon, a
snowflake , will flash.
1. Slide the SYSTEM switch to Cool and the FAN
switch to Auto.
2. Press the ▼key to lower the temperature setting
several degrees below the room temperature. After
approximately five minutes, the cooling equipment
should start. The fan starts and stops with the cool-
ing equipment.
3. Press the ▲key to raise the temperature setting
above the room temperature. Cooling system
should shut down.
Fan
1. Slide the SYSTEM switch to Off and the FAN
switch to On. The fan should run continuously.
2. Slide the FAN switch to Auto. In heating, the fan is
controlled directly by the heating equipment and
may start a few minutes after the heating equip-
ment turns on (on most systems). When using an
electric heat thermostat, the fan starts and stops
with the heating equipment. In cooling, the fan
starts and stops with the cooling equipment.
Consult the instructions provided with The Zone Panel to
troubleshoot system problems. Refer to Table 4 for the
thermostat’s Sequence of Operations.
Table 4. Thermostat Sequence of Operations.
Fan Selection System Selection Call Energize Display
Auto Off None None None
On Off None G None
Auto Cool None O None
Auto Cool Snowflake Symbol O, G, Y Snowflake Symbol
Auto Heat None B None
Auto Heat Flame symbol B, W* Flame symbol
*If fan operation (fuel) switch is in E position, G terminal is also energized.

69-1483—1 G.H. Rev. 2-02 www.honeywell.com/yourhome
T8401C ELECTRONIC THERMOSTATS
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