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T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS

68-0180-3

2

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.

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 cali-

brated 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; press-
ing 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, non-

condensing.

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.

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.

System

Cycles Per Hour

Steam, gravity

1

Hydronic heat, condensing 
gas furnaces

a

3

Special applications

b

4, 5

Gas or oil forced air (default) 

6

Electric heat

9

Special applications

b

12

Summary of Contents for T8401C

Page 1: ...ns 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 fo...

Page 2: ...ner 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 ...

Page 3: ...TION Disconnect power supply before beginning wiring to prevent electrical shock or equipment damage 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 questi...

Page 4: ...nd mount ing 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 wall plate at the desired location on the wall 2 Pull the thermostat wire through the entrance hole on the decorator cover plate t...

Page 5: ...ng 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 Fig 8 T8400 and T8401 wiring connections 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 M11023 ALTERNATE MOUNTING SCREW HOLE MOUNTING SCREW HO...

Page 6: ...mer Fig 12 T8424C D two stage heat and two stage cool system with manual changeover wiring diagram TERMINAL SCREW M20212 G R C Y W1 B O FOR STRAIGHT INSERTION STRIP 5 16 IN 8 MM FOR WRAPAROUND STRIP 7 16 IN 11 MM Y2 W2 L1 HOT L2 1 2 1 2 W Y G R C COOLING CONTACTOR FAN RELAY HEATING PRIMARY CONTROL 24V POWER SUPPLY PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED IN T8401C INSTALLATIONS...

Page 7: ...TALLATIONS CONNECT C TERMINAL 4 4 4 4 4 ZONE 1 VALVE OR DAMPER MOTOR ZONE 2 VALVE OR DAMPER MOTOR ZONE 3 VALVE OR DAMPER MOTOR ZONE 4 VALVE OR DAMPER MOTOR M10285A C C C 24V GND 24V S8610 L1 HOT L2 1 1 2 3 4 5 L8148E1265 4 2 3 3 FUSE 5 1 2 5 6 PRONG FEMALE MOLEX RECEPTABLE IN L8148E AND 5 PRONG MALE MOLEX PLUG ON CABLE 1K1 B1 B2 L1 C1 C2 L2 CIRCULATOR POLARIZED 4 PRONG MALE MOLEX PLUG AND 4 PRONG ...

Page 8: ...air circulation 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 M11025B FAN SYSTEM Auto On Cool Off Heat DASHED LINES INDICATE TABS ON BACK OF THERMOSTAT FAN SYSTEM Auto Cool Off Heat ENGAGE TABS AT TOP OF THERMOSTA...

Page 9: ...OTE 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 room temperature is displayed in F set the temperature setpoint to 52 F If the room temperature is dis played in C set the temperature setpoint to 11 C 2 Press the and keys simulta neously for more than one second to light all segments on displa...

Page 10: ... plus integral control maintains the same indoor temperature independent of the outdoor temperature Thus the T8400C and T8401C Thermostats provide tight temperature control with virtually no noticeable swings in temperature setpoint a condition referred to as droop This zero droop performance provides improved occupancy comfort Occupants do not need to continually adjust thermostat settings to be ...

Page 11: ...ps in the Operation section for typical energy savings Sequence of Operations The Fan Heat and Cool outputs are relay or mosfet controlled A loss of ac power or a change in the SYSTEM switch setting can cause the outputs to turn off The truth table shows the sequence of operations for the FAN settings and SYSTEM modes See Table 3 Sequence of Operations L1 HOT L2 1 1 POWER SUPPLY PROVIDE DISCONNECT...

Page 12: ...at and the fan switch to Auto 2 Press and hold the key to raise the temperature set ting several degrees above the room temperature After approximately ten seconds the W terminal is energized and the heating equipment starts 3 Press the key to lower the temperature setting below the room temperature Heating equipment should stop Cooling CAUTION Low Temperature Hazard Operating at too low of an out...

Page 13: ...NS HEATING OR COOLING EQUIPMENT INOPERATIVE REPLACE THERMOSTAT PARTIAL DISPLAY INOPERATIVE THERMOSTAT SEE THE SETTINGS AND ADJUSTMENTS SECTION FOR INSTRUCTIONS ON INSTALLER SETUP MODE STILL IN INSTALLER SETUP MODE RECONFIGURE THE DISPLAY SEE SETTINGS AND ADJUSTMENTS SECTION TEMPERATURE DISPLAY IS INCORRECT THERMOSTAT IS CONFIGURED FOR F OR C DISPLAY CHECK THAT C TERMINAL IS CONNECTED TO THE SYSTEM...

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