Honeywell T8424C User Manual
T8400C, T8401C and T8424C,D
Electronic Thermostats
PRODUCT DATA
FEATURES
T8400C and
T8401C
T8424C,D
APPLICATION
The T8400C and T8401C Standard Electronic Thermostats
provide single-stage, non-programmable temperature control
for 24V heating-cooling systems with manual changeover
from heat to cool.
The T8424C Electronic Multistage Thermostat provides twostage heat and one-stage cool control.
The T8424D Electronic Multistage Thermostat provides twostage heat and two-stage cool control.
• Attractive styling complements any decor to the
homeowner’s delight.
• Ease-of-use means fewer homeowner questions and
increased homeowner satisfaction.
• Large display for quick easy readability.
• Conveniently sized 3-1/2 x 3-1/2 thermostat with
optional decorator cover plates (3-7/8 in. x 3-7/8 in. and
5-3/4 in. x 5-3/4 in.) makes it easy to install in a variety
of locations.
• Keys are located for easy access.
• Fan and system switches are located on the lower
edge to eliminate accidental setting changes.
• Easy installation, setup and self-test saves time and
increases installer productivity.
• Manual changeover from heat to cool eliminates
unexpected system operation.
• °F or °C temperature display for added model
flexibility.
• Selectable heating cycle rate (1, 3, 4, 5, 6 or 9, 12 cph)
for a variety of applications which reduces the amount
of inventory.
• Cooling cycle rate is fixed (3 cph), the standard setting
for compressors, for speedy installation.
• Setpoints are permanently held in memory (no
batteries used) and retained during power outages for
increased installer and homeowner convenience.
• Power stealing and hard wired models available for
virtually all equipment and application needs including
gravity or radiating systems, hydronic heat,
condensing gas furnaces, gas or oil forced air and
electric heat.
® U.S. Registered Trademark
Copyright © 2001 Honeywell • All Rights Reserved
Contents
Application ........................................................................ 1
Features ........................................................................... 1
Specifications ................................................................... 2
Ordering Information ........................................................ 2
Installation ........................................................................ 3
Settings and Adjustments ................................................. 8
Operation .......................................................................... 10
Checkout .......................................................................... 12
Troubleshooting ................................................................ 13
68- 0180- 3
T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
SPECIFICATIONS
IMPORTANT
The specifications given in this publication do not
include normal manufacturing tolerances; therefore,
an individual unit might 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.
T8400C, T8401C, T8424C,D TRADELINE® models include a
thermostat, wallplate for wiring and mounting thermostat and
owner’s guide.
T8400C, T8401C SUPER TRADELINE® models include a
thermostat, wallplate (for mounting and wiring thermostat),
two decorator cover plates for covering wall marks (3-7/8 in. x
3-7/8 in. and 5-3/4 in x 5-3/4 in.), and owner’s guide.
Power:
T8400C: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
T8401C: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
T8424C,D: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
Electrical Ratings:
Heating: .02 to 1.5A run; 3.5A inrush.
Cooling: .02 to 1.5A run; 7.5A inrush.
Fan: .02 to 0.5A run; 2.5A inrush.
Current Draw:
T8400C Power Stealing Thermostat requires less than
0.25 mA current draw when the thermostat calls for heat
and is compatible with most 24V microprocessor systems.
The T8400C Power Stealing Thermostat can be used in
any non-millivolt application where the T8401C and
T8424C,D Hard Wired Thermostats cannot be used. For
further detail, see Power Stealing in the Operation section.
Temperature Adjustment:
Setpoint temperature is adjusted by using the ▲ or ▼
keys. One press changes the setpoint one degree; pressing and holding changes the setpoint several degrees.
Temperature Setting Range: 40°F (4°C) to 99°F (37°C).
Ambient Temperature Range: 40°F (4°C) to 110°F (43°C).
Shipping Temperature Range: -20°F (-29°C) to 120°F
(49°C).
Operating Relative Humidity: 5% to 90% RH, noncondensing.
Cycle Rates (at 50% Load):
Heating: Selectable at 1, 3, 4, 5, 6, 9 or 12 cph. See Table
1 for cycle rate options and corresponding system
equipment.
Cooling: Fixed at 3 cph.
Table 1. Heating Cycle Rates.
System Cycles Per Hour
Steam, gravity 1
Hydronic heat, condensing
gas furnaces
Special applications
Gas or oil forced air (default) 6
Electric heat 9
Special applications
a
High efficiency furnace.
b
Refer to equipment manufacturer’s instructions.
Finish:
T8400C, T8401C and T8424C,D TRADELINE® AND SUPER
TRADELINE®: Taupe finish.
T8400C, T8401C and T8424C,D STANDARD MODELS:
Premier White® finish and only available in builder packs of
20.
Accessory: Decorator cover plates (for covering wall marks):
5-3/4 in. x 5-3/4 in. and 3-7/8 in. x 3-7/8 in.
Dimensions: See Fig. 1 or 2.
a
b
b
3
4, 5
12
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 Home and Building Control Sales Office (check white pages of your phone directory).
2. Home and Building Control Customer Relations
Honeywell, 1985 Douglas Drive North
Golden Valley, Minnesota 55422 (800) 468-1502
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.
68-0180-3 2
T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
2-7/8
(78)
WALLPLATE THERMOSTAT
2-7/8 (78)
2-1/2 (64)
3-1/2 (89) 1-3/16
UP
W
1-1/2
Y
G
R
C
(37)
3-1/2
(89)
Room
Set
FAN SYSTEM
Auto On
Fig. 1. T8400/T8401 Thermostat dimensions in in. (mm).
WALLPLATE
4-3/8 (111)
3-5/16 (84)
INSTALLATION
When Installing this Product…
1. Read these instructions carefully. Failure to follow them
could damage the product or cause a hazardous condition.
2-3/8
(70)
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 opera-
THERMOSTAT
5-1/2 (140)
THERMOSTAT
AND WALLPLATE
1-3/16
(55)
tion as provided in these instructions.
CAUTION
Disconnect power supply before beginning wiring
to prevent electrical shock or equipment damage.
THERMOSTAT
AND WALLPLATE
(55)
Cool Off Heat
M10283A
Room
Set
FAN SYSTEM
Auto On
Cool Off Heat Em. Ht.
3-1/2
(89)
M18585
Fig. 2. T8424 Thermostat dimensions in in. (mm).
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 it properly.
Contact your local waste management authority for
instructions regarding recycling and the proper
disposal of the control. If you have questions, call the
Honeywell Customer Response Center at
1-800-468-1502.
3 68-0180-3
T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
Location
Install the thermostat about 5 ft (1.5m ) above the floor in an
area with good air circulation at average temperature. See
Fig. 3. Do not install the thermostat where it can be affected
by:
— drafts or dead spots behind doors and in corners.
NO
NO
— 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.
YES
NO
5 FEET
[1.5 METERS]
Fig. 3. Typical location of thermostat.
Mounting Decorator Cover Plate and
Wallplate to Wall
IMPORTANT
Level for appearance only. The thermostat functions
normally even when not mounted level.
NOTE: The TRADELINE® models include a thermostat and
wallplate (for wiring and mounting thermostat).
T8400C, T8401C SUPER TRADELINE® models
include a thermostat, wallplate (for wiring and mounting thermostat) and two decorator cover plates (for
covering wall marks).
Mount decorator cover plate (SUPER TRADELINE® model
only), wallplate, T8400C, T8401C or T8424C,D, and the
screws provided (see Fig. 4 or 5) as follows:
1. Place the desired decorator cover plate and the wallplate at the desired location on the wall.
2. Pull the thermostat wire through the entrance hole on
the decorator cover plate, then through the wallplate
entrance hole.
3. Select the two mounting holes that best fit the application.
4. Fasten the decorator cover plate and the wallplate to
the wall using the screws provided.
5. After wiring the wallplate, plug the hole to prevent drafts
from affecting the thermostat; see Wiring section.
M10308
5-3/4 IN. x 5-3/4 IN.
DECORATOR
COVER PLATE
WALL
1
WALL
ANCHORS (2)
1
3-7/8 IN. x 3-7/8 IN. DECORATOR COVER PLATE (SELECT MODELS).
DRILL 3/16 INCH HOLES (IF DRYWALL) OR 7/32 (PLASTER OR WOOD)
2
WHEN USING WALL ANCHORS.
M11041C
Fig. 4. Mounting the T8400 and T8401 decorator
cover plate and wallplate to wall.
2
68-0180-3 4
T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
WALL
1
MOUNTING
SCREWS (2)
1
WHEN USING WALL ANCHORS, DRILL 3/16 INCH
HOLES FOR DRYWALL, 7/32 INCH HOLES FOR
PLASTER OR WOOD.
WALL
ANCHORS (2)
WALLPLATE
M12202A
Fig. 5. Mounting the T8424 wallplate to wall.
Wiring
IMPORTANT
Use an 18-gauge maximum wire for wiring the thermostats.
All wiring must comply with local electrical codes and
ordinances. Disconnect the power supply to prevent electrical
shock or equipment damage.
KEEP WIRING IN
SHADED AREA
MOUNTING
SCREW HOLE
G
C
R
W1
Y
WIRING ENTRANCE
HOLE
W2
Y2
B
O
MOUNTING
SCREW HOLE
NOTE: To ensure proper mounting of thermostat, restrict all
wiring to the shaded area on the left side of the terminals. See Fig. 6 or 7.
KEEP WIRING IN
SHADED AREA
WIRING ENTRANCE HOLE
MOUNTING
SCREW HOLE
ALTERNATE MOUNTING
SCREW HOLE
W
Y
G
R
C
MOUNTING
SCREW
HOLE
ALTERNATE
MOUNTING
SCREW HOLE
M11023
Fig. 6. Restrict T8400 and T8401 wiring to shaded area.
M20211
Fig. 7. Restrict T8424 wiring to shaded area.
The shape of the terminals permits insertion of straight or
wraparound wiring connections; either method is acceptable.
See Fig. 8 or 9.
W
Y
G
FOR WRAPAROUND
STRIP 7/16 IN. (11 MM)
R
FOR STRAIGHT INSERTION
STRIP 5/16 IN. (8 MM)
C
TERMINAL SCREW
M11232
Fig. 8. T8400 and T8401 wiring connections.
5 68-0180-3
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