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™
T8775A,C The Digital Round  
Non-Programmable Thermostats  
PRODUCT DATA  
FEATURES  
•
•
Attractive styling complements any decor.  
Simple to use. Turn the dial to adjust the setpoint  
temperature.  
•
•
•
Large easy-to-read display. The temperature reading is  
easily seen from a distance.  
Backlit display. On-demand backlighting makes it easy  
to read the display in a dark room or hallway.  
No batteries required. The setpoint temperature is held  
permanently in memory in the event of a power failure.  
•
•
•
Powered through heating-cooling system controls.  
System and Fan switches on the T8775C model.  
Manual changeover from heat to cool on T8775C  
model.  
APPLICATION  
•
Easy installation and set up saves time and increases  
installer productivity.  
The T8775A and T8775C Thermostats provide single-stage,  
non-programmable temperature control for 24 Vac systems  
with manual changeover from heat to cool.  
•
•
Easily configurable by the use of DIP switches.  
Fahrenheit or Celsius temperature display for added  
flexibility.  
The T8775A controls 2-wire heating-only systems.  
The T8775C controls gas, oil or electric heating and cooling  
systems.  
•
•
•
•
Selectable heating cycle rates (1, 3, 6, 9 CPH) for a  
variety of applications.  
Cooling cycle rate is fixed at 3 CPH. This is the  
standard compressor setting.  
Minimum off-time for the compressor in the cooling  
mode. Protects and extends the life of the equipment.  
Decorative cover plate is available to cover marks on  
the wall or to mount the T8775 Thermostat to an  
electrical box.  
Contents  
Application.........................................................................1  
Features ............................................................................1  
Specifications ....................................................................2  
Ordering Information .........................................................2  
Installation .........................................................................3  
Wiring ................................................................................4  
Customize Thermostat ......................................................5  
Set System and Fan Switches ..........................................6  
Checkout ...........................................................................7  
Troubleshooting Guide ......................................................8  
®
U.S. Registered Trademark • Patents Pending  
Copyright © 2004 Honeywell International Inc.  
All Rights Reserved  
68-0279  
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
Ambient Range:  
SPECIFICATIONS  
4
0°F to 110°F (4.4°C to 43.3°C).  
Shipping Temperature Range:  
IMPORTANT  
The specifications given in this publication do not  
-20°F to 120°F (-28.9°C to 48.9°C).  
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.  
Humidity Ratings: 5% to 90% RH, non-condensing.  
Mounting Hardware:  
Sheet metal screws: Two 1-in. (25 mm) 4-24, type AB.  
Drywall anchors: Two conical anchors, 3/16 in. (5 mm)  
diameter by ¾ in. (19 mm) length.  
Models: T8775A and T8775C TRADELINE® models include  
a thermostat, wallplate for mounting and wiring, mounting  
hardware, 4074FAB resistor, installation instructions and an  
owner’s guide.  
4
074 FAB Resistor:  
Kohm, 3 Watts.  
1
Installation Instructions packed with resistor.  
Batteries: Not required.  
Electrical Ratings:  
2
4 Vac nominal: 18 Vac to 30 Vac, 60Hz.  
Finish: Premier White®.  
Heating: .02 to 1.5 A run; 3.5A inrush.  
Cooling: .02 to 1.5 A run; 6.0 A inrush.  
Fan: .02 to 0.5 A run; 2.5A inrush.  
Accessories:  
5
0000066-001 Decorative Cover Plate. Used to cover wall  
marks, or to mount T8775 Thermostat to an electrical box.  
2007680-001 Cover Ring.  
Temperature Ratings:  
Setting Range:  
3
4
4
0°F to 90°F (4.5°C to 32.0°C) in heating.  
5°F to 99°F (7.0°C to 37.0°C) in cooling.  
Dimensions: See Fig. 1.  
1
-7/16  
2-5/8 (67)  
(
37)  
3
-11/16  
ROOM  
SET  
(94)  
M19676  
Fig. 1. T8775 Thermostat dimensions in in. (mm).  
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).  
Honeywell Customer Care  
2.  
1
885 Douglas Drive North  
Minneapolis, Minnesota 55422-4386  
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.  
68-0279  
2
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
INSTALLATION  
YES  
RS E  
O
T
OM  
NO  
NO  
5
FEET  
[
1.5 METERS]  
NO  
M19716A  
Fig. 2. Typical thermostat location.  
Mount wallplate to wall (See Fig. 4) as follows:  
Separate Wallplate from Thermostat  
1.  
Place your thumbs on top of the thermostat and wall-  
plate. Use your thumbs to pull the thermostat away from  
the wallplate. See Fig. 3.  
WALL ANCHORS (2)  
WALL PLATE  
WALL PLATE  
TOP OF  
THERMOSTAT  
1
M19679  
WIRING HOLE  
1
INCH SCREW (2)  
M19499  
Fig. 3. Separate wallplate from thermostat.  
1
WHEN USING WALL ANCHORS, DRILL 3/16 IN. HOLES  
FOR DRYWALL, 7/32 IN. HOLES FOR PLASTER.  
Mount Wallplate to Wall  
Fig. 4. Mount wallplate to wall.  
1.  
2.  
3.  
Pull the thermostat wires through the wiring hole on the  
wallplate.  
Use a pencil to mark the center of the screw holes on  
the left and right sides of the wallplate.  
NOTE: Level wallplate for appearance only. The thermostat  
functions normally even when not mounted level.  
Remove the wallplate from the wall and drill two 3/16 in.  
(
5 mm) holes in the wall (if drywall) at the locations you  
marked. For materials such as plaster, drill 7/32 in.  
6 mm) holes where marked.  
(
3
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
4
.
.
Tap the provided wall anchors into the drilled holes until  
they are flush with the wall.  
Pull the thermostat wires through the wiring hole on the  
wallplate and reposition the wallplate over the wall  
anchors.  
Refer to Fig. 7 through 11 for typical wiring diagrams.  
5
6
.
.
Attach the wallplate to the wall with the screws pro-  
vided.  
After wiring the wallplate, plug the hole to prevent drafts  
from affecting the thermostat; see Wiring section.  
7
R
W
WIRING  
HEATING  
RELAY OR  
1
IMPORTANT  
VALVE COIL  
Use 18-gauge wire to wire the T8775A,C  
Thermostats.  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
All wiring must comply with local electrical codes and  
ordinances. Disconnect the power supply to prevent electrical  
shock or equipment damage.  
M19513  
Fig. 7. Typical hookup of T8775A in a heat-only system.  
NOTE: To ensure proper mounting of thermostat, restrict all  
wiring to the shaded area. See Fig. 5.  
O
B
Rc  
MOUNTING  
HOLES  
2
G
Y
R
W
HEATING  
1
FAN  
RELAY  
RELAY OR  
VALVE COIL  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
WIRING  
HOLE  
RESTRICT WIRING  
TO SHADED AREA  
FACTORY INSTALLED JUMPER.  
M19514  
M19680  
Fig. 8. Typical hookup of T8775C in heat-only system with  
fan.  
Fig. 5. Restrict T8775 wiring to shaded area.  
The shape of the terminals permits insertion of straight or  
wraparound wiring connections; either method is acceptable.  
See Fig. 6.  
O
B
Rc  
2
G
Y
R
FOR STRAIGHT INSERTION  
STRIP 5/16 IN. (8 MM).  
W
FOR WRAPAROUND  
INSERTION STRIP  
1
HEATING  
COMPRESSOR  
CONTACTOR  
FAN  
RELAY  
RELAY OR  
7/16 IN. (11 MM).  
VALVE COIL  
M19496  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
Fig. 6. T8775 wiring connections.  
FACTORY INSTALLED JUMPER.  
M19515  
Fig. 9. Typical hookup of T8775C in heat-cool system with  
single transformer.  
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
B
Rc  
R
G
Y
2
W
COMPRESSOR  
CONTACTOR  
HEATING  
RELAY OR  
VALVE COIL  
FAN  
RELAY  
1
1
FUEL SWITCH  
M19497  
Fig. 12. Fuel switch.  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
DIP Switch  
REMOVE FACTORY INSTALLED JUMPER BETWEEN R AND RC.  
To adjust the heat cycle rate or the Fahrenheit/Celsius  
temperature display, locate DIP switch 1, 2 and 3 on the back  
of the thermostat. See Fig. 13.  
M19517  
Fig. 10. Typical hookup of T8775C in heat-cool system  
with two transformers.  
BACK OF THERMOSTAT  
4
O
B
Rc  
G
2
Y
3
R
W
HEAT  
CHANGEOVER  
VALVE  
COMPRESSOR  
CONTACTOR  
1
FAN  
RELAY  
COOL  
CHANGEOVER  
VALVE  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
M19567  
DIP SWITCH  
2
3
4
FACTORY INSTALLED JUMPER.  
USE A JUMPER WIRE (NOT SUPPLIED) TO CONNECT W TO Y.  
Fig. 13. DIP switch.  
USE EITHER O OR B FOR HEAT PUMP CHANGEOVER.  
M19516  
Set Heat Cycle Rate  
Use DIP switches 1 and 2 to set the heat cycle rate. See  
Table 1.  
Fig. 11. Typical hookup of T8775C in single-stage heat  
pump system.  
Table 1. Heat Cycle Rate.  
CUSTOMIZE THERMOSTAT  
Cycles DIP  
Per Switch Switch  
Hour  
DIP  
Heating System  
Steam, Gravity  
1
2
Setting Fuel Switch (T8775C only)  
1
On  
Off  
On  
On  
The fuel switch is preset at the factory in the F position. See  
Fig. 12. This is the correct setting for gas or oil systems. If the  
T8775C is being installed on an electric heat system, or a heat  
pump, set the switch to the E position. The E position allows  
the fan to turn on immediately with the heating equipment in a  
system where the G terminal is connected.  
High Efficiency Warm Air (90%+  
efficiency), Hot Water, Heat Pump  
3
Gas or Oil Warm Air (factory setting)  
Electric Warm Air  
6
9
Off  
On  
Off  
Off  
In Floor Radiant Heat  
Check with manufacturer  
for recommended cycle  
rate.  
5
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
Fahrenheit/Celsius Indication  
Use DIP switch 3 to set the desired temperature indication. See  
Table 2.  
(T8775C ONLY)  
SELECTS  
ON/AUTO  
(
T8775C ONLY)  
Table 2. Temperature Indication.  
SELECTS  
COOL/OFF/HEAT  
Fahrenheit/Celsius Display  
DIP Switch 3  
Fahrenheit (factory setting)  
Celsius  
Off  
On  
ROOM  
SET  
SHOWS THAT THE  
CURRENT ROOM  
TEMPERATURE IS  
DISPLAYED.  
Mount Thermostat to Wallplate (see Fig. 14)  
SHOWS THAT THE  
CURRENT TEMPERATURE  
SETPOINT IS DISPLAYED.  
ENGAGE TABS  
AT BOTTOM OF  
THERMOSTAT  
DISPLAYS ROOM  
OR SET TEMPERATURE  
DISPLAYS AND ADJUSTS  
TEMPERATURE SETPOINT/TURNS  
BACKLIGHT ON  
AND WALL PLATE.  
M19681  
PRESS UPPER  
EDGE OF CASE  
TO LATCH  
Fig. 15. T8775 Thermostat (features and operation).  
ROOM  
SET  
M19498  
Fig. 14. Mount thermostat to wallplate.  
SET SYSTEM AND FAN SWITCHES  
(T8775C ONLY)  
SYSTEM Switch: (See Fig.15)  
M19582  
Heat: The thermostat controls the heating system.  
Off: Both the heating and cooling systems are off.  
Cool: The thermostat controls the cooling system.  
Fig. 16. T8775 Thermostat.  
Backlit Display  
FAN Switch: (See Fig.15)  
Push the backlight button to turn on the backlight (See Fig.  
Auto: The fan only runs with the heating and cooling  
15).  
system.  
On: The fan runs continuously. Use for improved air  
circulation.  
Display Temperature Setpoint  
1.  
Turn the dial one click to display the temperature set-  
point. An indicator points to Set when the tempera-  
FEATURES AND OPERATION  
Features and operation of The Digital RoundTM Thermostat (see  
ture setpoint is displayed (see Fig.17).  
Fig. 15 and 16):  
ROOM  
SET  
•
•
•
•
Simple to use. Turn the dial to adjust the temperature  
setting.  
Large easy-to-read display. The temperature reading is  
easily seen from a distance.  
Backlit display. On-demand backlighting makes it easy to  
read the display in a dark room or hallway.  
No batteries required. The temperature setting is held  
permanently in memory in the event of a power failure.  
M19489  
Fig. 17. Temperature setpoint display.  
2.  
If a change to the temperature setpoint is not made  
within five seconds, the display will switch to the current  
room temperature. An  
indicator points to Room  
when the room temperature is displayed (see Fig. 18).  
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
Table 3. T8775 Power Stealing.  
Power Stealing Circuit  
ROOM  
SET  
System Switch  
Heat  
T8775A  
R and W  
T8775C  
R and W  
M19490  
Off  
—
—
R and W  
Rc and Y  
Cool  
Fig. 18. Room temperature display.  
The T8775 Thermostat only operates when mounted on the  
wallplate with 24 Vac applied. Batteries are not required for  
operation because the temperature setpoint is permanently  
retained in memory.  
Adjust Temperature Setpoint  
Turn the dial clockwise to raise the temperature setpoint. Turn  
the dial counterclockwise to lower the temperature setpoint  
(see Fig. 16).  
Sequence of Operations  
See Table 4 for Sequence of Operations.  
Power Stealing  
The T8775 thermostat steals power from R and W or Rc and  
Y depending on the system switch position. See Table 3.  
Table 4. Sequence of Operations.  
System Switch Settings Call for Action  
Off None  
Fan Switch Settings  
Auto  
Energize Terminals  
Display Icons  
None  
None  
Auto  
Auto  
Heat  
Cool  
Heating  
Cooling  
Wa  
Flame  
Y,G  
Snowflake  
None  
On  
On  
Off  
Fan  
G
Heat  
Heating  
W,G  
Flame  
On  
Cool  
Cooling  
Y,G  
Snowflake  
a
If fuel switch is set to E, both W and G are energized in a call for heat.  
1
.
.
Slide the system switch to COOL and the fan switch to  
AUTO.  
Lower the temperature setpoint several degrees below  
CHECKOUT  
2
the room temperature.  
Cooling (T8775C only)  
3
.
.
A snowflake  
will appear in the display and the cool-  
ing should turn on.  
Raise the temperature setpoint several degrees above  
the room temperature.  
4
CAUTION  
Low Temperature Hazard.  
5. The snowflake will disappear from the display and  
the cooling should turn off.  
Operating at too low of an outdoor temperature  
may cause compressor damage.  
Do not operate cooling if outdoor temperature is below  
Heating  
50°F (10°C). Refer to manufacturer’s  
recommendations.  
1. Slide the system switch to HEAT and the fan switch to  
AUTO (T8775C only).  
2
3
4
5
.
.
.
.
Raise the temperature setpoint several degrees above  
the room temperature.  
A flame will appear in the display and the heat should  
turn on.  
Lower the temperature setpoint below the room temper-  
ature.  
Minimum Off-Timer  
The minimum off-timer in the T8775C Thermostat assures  
that the cooling compressor does not turn on for at least five  
minutes after it turns off. The snowflake will flash in the display  
if there is a call for cooling during the 5-minute off-time.  
The flame will disappear from the display and the  
heat should turn off.  
The following activates the 5-minute minimum-off timer:  
•
•
•
Initial startup  
Power interruption  
Compressor turns off:  
Fan  
1.  
Slide the system switch to OFF and the fan switch to  
ON. The fan should run continuously.  
Slide the fan switch to AUTO. The fan should turn off.  
—
—
—
Setpoint is raised above the room temperature  
System switch is changed from the cool mode  
Thermostat ends the call for cooling  
2.  
NOTE: Make sure that all equipment responds properly to  
the thermostat.  
NOTE: The 5-minute minimum-off timer does not apply to  
heating.  
7
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T8775A,C THE DIGITAL ROUND™ NON-PROGRAMMABLE THERMOSTATS  
TROUBLESHOOTING GUIDE  
HEATING OR COOLING EQUIPMENT  
WILL NOT OPERATE.  
NO AC POWER TO THERMOSTAT.  
• CHECK POWER TO HEATING AND COOLING EQUIPMENT  
–
–
–
ON-OFF SWITCH  
FUSE OR CIRCUIT BREAKER  
LOOSE 24V CONNECTION:  
–
–
AT THERMOSTAT  
AT FURNACE/AIR CONDITIONER  
–
INCORRECT WIRING (SEE WIRING DIAGRAMS)  
THERMOSTAT INOPERATIVE.  
SEE CHECKOUT SECTION.  
PRESENT SETTING TOO LOW/HIGH.  
ADJUST TEMPERATURE BY TURNING DIAL CLOCKWISE OR  
COUNTER-CLOCKWISE.  
SYSTEM SWITCH ON THERMOSTAT  
IN WRONG POSITION.  
RESET THERMOSTAT SYSTEM SWITCH.  
MINIMUM-OFF TIME IN COOLING.  
WAIT UP TO FIVE MINUTES FOR THE COOLING EQUIPMENT  
TO TURN ON.  
INCORRECT WIRING.  
CHECK WIRING DIAGRAMS.  
HEATING OR COOLING EQUIPMENT  
INOPERATIVE.  
CONSULT EQUIPMENT MANUFACTURER INSTRUCTIONS.  
PARTIAL DISPLAY  
INOPERATIVE THERMOSTAT.  
REPLACE THERMOSTAT.  
NO DISPLAY  
NO POWER TO THERMOSTAT.  
• CHECK POWER TO HEATING AND COOLING EQUIPMENT  
–
–
–
ON-OFF SWITCH  
FUSE OR CIRCUIT BREAKER  
LOOSE 24V CONNECTION:  
–
–
AT THERMOSTAT  
AT FURNACE/AIR CONDITIONER  
–
INCORRECT WIRING (SEE WIRING DIAGRAM)  
THERMOSTAT MOUNTED  
SEE MOUNT THERMOSTAT TO WALLPLATE SECTION.  
INCORRECTLY ON WALLPLATE.  
TEMPERATURE DISPLAY IS  
INCORRECT.  
THERMOSTAT IS CONFIGURED FOR  
F OR C DISPLAY.  
RECONFIGURE THE DISPLAY. SEE CUSTOMIZE  
THERMOSTAT SECTION.  
TEMPERATURE SETTINGS WILL NOT  
CHANGE. (EX: CANNOT SET THE  
HEATING HIGHER OR THE  
COOLING LOWER).  
THE UPPER OR LOWER  
TEMPERATURE LIMITS WERE  
REACHED.  
CHECK THE TEMPERATURE SETPOINTS; TEMPERATURE  
SETTING RANGE IS 40 F TO 90 F (4.5 C TO 32 C) IN HEATING  
AND 45 F TO 99 F (7 C TO 37 C) IN COOLING.  
FAN DOES NOT OPERATE PROPERLY  
IN HEAT OR COOL MODES.  
INCORRECT WIRING.  
CHECK WIRING DIAGRAMS.  
CHECK FUEL SWITCH POSITION.  
SEE CUSTOMIZE THERMOSTAT SECTION.  
CONSULT EQUIPMENT MANUFACTURER INSTRUCTIONS.  
HEATING OR COOLING EQUIPMENT  
INOPERATIVE.  
M19684  
Automation and Control Solutions  
Honeywell International Inc.  
985 Douglas Drive North  
Golden Valley, MN 55422  
Honeywell Limited-Honeywell Limitée  
1
35 Dynamic Drive  
Scarborough, Ontario  
M1V 4Z9  
Printed in U.S.A. on recycled  
paper containing at least 10%  
post-consumer paper fibers.  
68-0279 J.S. 4-04  
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