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T8501D  
Deluxe Zone Thermostat  
INSTALLATION INSTRUCTIONS  
APPLICATION  
The T8501 Deluxe Zone Thermostat provides electronic control of 24 Vac single-stage zoned heating and cooling systems.  
Refer to Table 1 for a general description of the thermostat.  
Table 1. Description of T8501 Thermostat.  
Model  
Application  
Powering Method  
Requires common wire to Automatic or Heat-Off-Cool-Auto  
power supply Manual  
Changeover System Selection Fan Selection  
T8501D Zone 1 on MABS II or  
TotalZone® system  
On-Auto  
Do not install the thermostat where it can be affected by:  
RECYCLING NOTICE  
If this control is replacing a control that contains  
mercury in a sealed tube, do not place your old  
control in the trash.  
—
—
—
—
—
drafts, or dead spots behind doors and in corners.  
hot or cold air from ducts.  
radiant heat from sun or appliances.  
concealed pipes and chimneys.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
Contact your local waste management authority for  
instructions regarding recycling and the proper  
disposal of the old thermostat.  
Wallplate Installation  
The thermostat can be mounted horizontally on the wall or  
on a 2 in. x 4 in. wiring box. Position wallplate horizontally  
on the wall or on a 2 in. x 4 in. wiring box.  
INSTALLATION  
1
.
Position and level the wallplate (for appearance  
only). The thermostat will function properly even  
when not level.  
When Installing this Product…  
1.  
Read these instructions carefully. Failure to follow  
the instructions can damage the product or cause a  
hazardous condition.  
2. Use a pencil to mark the mounting holes. See Fig. 2.  
3. Remove the wallplate from the wall and drill two  
3/16 inch holes in the wall (if drywall) as marked. For  
firmer material such as plaster, drill two 7/32 inch  
holes. Gently tap anchors (provided) into the drilled  
holes until flush with the wall.  
4. Position the wallplate over the holes, pulling wires  
through the wiring opening.  
5. Loosely insert the mounting screws into the holes.  
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.  
After completing installation, use these instructions  
to check out the product operation.  
4
6. Tighten mounting screws.  
Location  
Install the thermostat about 5 ft (1.5m) above the floor in  
an area with good air circulation at average temperature.  
See Fig. 1.  
®
U.S. Registered Trademark  
Copyright © 1997 Honeywell Inc. •  
•
All Rights Reserved  
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T8501D DELUXE ZONE THERMOSTAT  
YES  
NO  
NO  
5
FEET  
[
1.5 METERS]  
NO  
M10106  
Fig. 1. Typical location of thermostat.  
Wiring  
WALL  
All wiring must comply with local electrical codes and  
ordinances. Refer to Fig. 3 and 4 for typical hookups. A  
letter code is located near each terminal for identification.  
WIRES  
THROUGH WALL  
CAUTION  
Disconnect power before wiring to prevent  
electrical shock or equipment damage.  
WALL  
1. Loosen the terminal screws on the wallplate and  
ANCHORS  
(2)  
connect the system wires. See Fig. 5.  
IMPORTANT  
Use 18 gauge, color-coded thermostat cable for  
proper wiring.  
2
.
Securely tighten each terminal screw.  
MOUNTING  
HOLES  
3. Push excess wire back into the hole.  
4.  
Plug the hole with nonflammable insulation to  
prevent drafts from affecting the thermostat.  
MOUNTING  
SCREWS  
M6530  
Fig. 2. Mounting the wallplate.  
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T8501D DELUXE ZONE THERMOSTAT  
OUTDOOR  
TEMPERATURE  
SENSOR  
Mounting Thermostat  
1. Engage tabs at the top of the thermostat and  
wallplate. See Fig. 6.  
(
OPTIONAL)  
THERMOSTAT  
2. Press lower edge of case to close and latch.  
O
G
B
C
W
R
Y
OT OT  
NOTE: To remove the thermostat from the wall, first pull out  
at the bottom of the thermostat; remove top last.  
ZONE 1  
T8  
A. ENGAGE TABS AT TOP OF THERMOSTAT AND WALLPLATE.  
T7  
T6  
T5  
T4  
O1  
G1  
B1  
E1  
CHANGEOVER  
CONTROL  
M1  
M12187  
Fig. 3. Typical wiring diagram for T8501D with zone 1  
MABS II control panel.  
B. PRESS LOWER EDGE OF CASE TO LATCH.  
THERMOSTAT  
O
B
G
Y
R
W
C
OT OT  
OUTDOOR  
THERMOSTAT  
SENSOR  
(OPTIONAL)  
M6798A  
W2  
L
G
Y
R
W
M6 M4 M1  
Fig. 6. Mounting thermostat on wallplate.  
TotalZone® PANEL THERMOSTAT CONNECTIONS M12186  
Fig. 4. Typical wiring diagram for T8501D with zone 1  
TotalZone® control panel.  
Using Thermostat Keys  
The thermostat keys are used to:  
•
•
•
•
•
•
•
set temperature,  
display present setting,  
configure Installer Setup,  
check System-Test,  
display outdoor temperature (select models),  
set the system operation,  
set the fan operation.  
See Fig. 7 for the location of the keys.  
INCREASE  
TEMPERATURE  
SETTING  
DECREASE  
TEMPERATURE  
SETTING  
i
FOR STRAIGHT  
INSERTION STRIP  
DISPLAY PRESENT  
SETTINGS AND SCROLL  
THROUGH INSTALLER  
SETUP MODES  
FOR WRAPAROUND  
5/16 IN. (8 MM).  
INSERTION STRIP  
/16 IN. (11 MM).  
7
M4826  
(INFORMATION KEY)  
M6801  
Fig. 5. Proper wiring technique.  
Fig. 7. Key locations and descriptions.  
3
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T8501D DELUXE ZONE THERMOSTAT  
The Installer Setup is used to customize the thermostat to  
specific systems. Some of the options include temperature  
display, changeover and outdoor temperature display.  
Installer Setup numbers are listed in Table 2. The table  
includes all the configuration options and the factory  
settings for the T8501.  
SETTINGS  
System and Fan Settings  
System settings control the thermostat operation as  
follows:  
Heat: The thermostat controls the heating.  
Off: Both the heating and cooling are off.  
Cool: The thermostat controls the cooling.  
Auto: The thermostat automatically changes between  
heating and cooling operation, depending on the  
indoor temperature.  
A combination of key presses are required to use the  
Installer Setup feature.  
—
To enter the Installer Setup, press and hold the  
Information key with the increase ▲ and decrease  
i
▲ keys until the first number is displayed. All display  
segments appear for approximately three seconds  
before the number is displayed. See Fig. 9 and 10.  
To advance to the next Installer Setup, press the  
Information i key.  
To change a setting, use the increase ▲ and de-  
crease ▲ keys.  
Fan settings control the system fan as follows:  
On: Fan operates continuously.  
Auto: Fan operates with equipment.  
—
—
—
The system default setting is Heat and the fan default  
setting is Auto. Use the keyboard to change to the desired  
settings. See Fig. 8.  
To exit the Installer Setup, press and hold the  
Information i key until the display returns to normal  
approximately three seconds). The display will scroll  
(
the numbers backwards to get to the normal display.  
The Installer Setup is automatically exited if no key  
presses are made for ten minutes.  
i
System  
System  
Fan  
Em Ht Temporary Setting  
Aux Ht  
Remote  
Room  
Press to select  
heating or cooling  
equipment.  
Press to select  
heating or cooling  
equipment.  
Em. Ht.-Emergency heating  
Heat— Heating equipment  
On— Fan runs continuously  
Auto—Fan runs when  
heating or cooling  
Off  
— No equipment  
System  
Fan  
Cool—Cooling equipment  
Auto—Thermostat  
automatically selects  
heating and cooling  
equipment.  
equipment operates  
Fan  
%Humid  
Outdoor  
Heat Cool  
Repl  
1
Batt  
Wait  
System  
Fan  
Em HeatOffCool Auto Only OnAuto  
M4844  
1
CHECK LIGHT ON SELECT MODELS  
M10147  
Fig. 9. Display of all the segments of the LCD.  
Fig. 8. Thermostat System and Fan key location.  
INSTALLER SETUP  
MODE NUMBER DISPLAY  
(
COLUMN 2 OF TABLE 2)  
NOTE: Always press the keys with your fingertip or  
similar blunt tool. Sharp instruments like a pen or  
pencil point can damage the keyboard.  
FACTORY SETTING OR  
OTHER CHOICE DISPLAY  
COLUMN 3 OR 5 OF TABLE 2)  
(
Temperature Settings  
The default setpoint for heat is 70°F (21°C) and for cool is  
7
8°F (25.5°C). Press the increase ▲ or decrease ▲ key to  
change the present setting to change between heat and  
cool, press the Information key until the setting to be  
i
changed appears. Press the increase ▲ or decrease ▲  
key to adjust the setting.  
M10105A  
INSTALLER SETUP  
Fig. 10. Display of Installer Setup number and setting.  
NOTE: For most applications, the thermostat factory-  
settings will not need to be changed. Review the  
factory settings in Table 2 and if no changes are  
necessary, go to the Installer System-Test  
section.  
IMPORTANT  
Only configurable numbers are shown on the  
device. Example: If thermostat does not have  
outdoor temperature capability, Installer Setup  
Number 24 will not be displayed. Review Table 2  
factory-settings and mark any desired changes in  
the Actual Settings column. When Installer Setup  
is complete, review the settings to confirm that  
they match the system.  
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T8501D DELUXE ZONE THERMOSTAT  
Table 2. Thermostat Installer Setup Options.  
Installer Setup  
Number  
Other Choices  
(Press ▲ or ▲ key to change)  
(Press  
i
key  
Factory Setting  
Description  
—
Conventional applica-  
tions where equipment  
controls fan operation  
in heat mode  
Actual  
Setting  
Select  
Not used  
Fan operation  
to change) Display  
Display  
Description  
01  
02  
—
00  
—
01  
—
—
a
Heat pump and electric heat  
applications where thermostat  
controls fan operation in heat  
mode  
Not used  
Heating cycle  
rate  
03  
04  
—
06  
—
—
—
—
6 cph used for  
conventional systems  
01, 03, 01—1 cph used for radiant floor  
or 09 heat, gravity systems  
0
3—3 cph used for hot water  
systems or high efficiency  
furnaces  
09—9 cph used for electric heat  
systems  
Not used  
Changeover  
05 thru 11  
12  
—
01  
—
—
—
—
—
Manual changeover  
00 or 00—Manual changeover  
02—Auto only  
02  
Not used  
Degree  
temperature  
display  
13  
14  
—
00  
—
—
01  
—
Temperature is  
displayed in °F  
Temperature is displayed in °C  
Not used  
15 thru 18  
19  
—
00  
—
—
01  
—
—
Extended fan  
operation in  
No extended fan  
operation after the call  
for heat ends  
Fan operation is extended  
90 seconds after the call for  
heat ends  
a,b  
heating  
Extended fan  
operation in  
cooling  
20  
00  
No extended fan  
operation after the call  
for cool ends  
01  
Fan operation is extended  
90 seconds after the call for  
cool ends  
a,b  
Not used  
Outdoor  
21 thru 23  
24  
—
00  
—
—
01  
—
—
—
No outdoor  
temperature is  
displayed  
Outdoor temperature is  
displayed. Needs a C7089B1000  
Outdoor Sensor to operate.  
temperature  
b
display  
Not used  
25 thru 32  
33  
—
05  
—
—
—
Minimum off  
time for the  
compressor  
5 minute minimum off 00, 01, Minimum number of minutes  
time for the 02, 03 (0 thru 5) the compressor will be  
compressor or 04 off between calls for the  
compressor  
Heating setpoint  
range stop  
34  
35  
36  
90  
48  
00  
Heating setpoint can  
be set no higher than  
40 thru Number can be set anywhere  
b
90  
between 40 and 90 in 1°F  
increments  
90°F  
Cooling setpoint  
Cooling setpoint can  
be set no lower than  
48 thru Number can be set anywhere  
b
range stop  
99  
between 48 and 99 in 1°F  
increments  
48°F  
System on  
indicator  
LCD On symbol is  
displayed when  
01  
Display is disabled  
(
flame=heat,  
system is energized  
snowflake=cool)  
is displayed  
b
Temperature  
display  
adjustment  
37  
00  
No difference in -3 thru 01—Display adjusts to 1°F higher  
displayed temperature 03 than actual room temperature  
and actual room 02—Display adjusts to 2°F higher  
temperature than actual room temperature  
0
3—Display adjusts to 3°F higher  
than actual room temperature  
1—Display adjusts to 1°F lower  
than actual room temperature  
2—Display adjusts to 2°F lower  
than actual room temperature  
3—Display adjusts to 3°F lower  
than actual room temperature  
-
-
-
a
b
Number 02 must be set to 01 to extend fan operation.  
Available on select models.  
5
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T8501D DELUXE ZONE THERMOSTAT  
IMPORTANT  
Review the settings to confirm that they match  
the system. To exit the Installer Setup, press and  
hold the Information  
Em Ht Temporary Setting  
Aux Ht  
Remote  
Room  
i key until the display  
%Humid  
returns to normal (approximately three seconds).  
Outdoor  
Heat Cool  
System Fan  
Em HeatOffCool Auto Only OnAuto  
Repl  
Batt  
Wait  
INSTALLER SYSTEM-TEST  
Use the Installer System-Test to check the thermostat  
operation. Refer to Table 3 for a list of the available  
system-tests.  
M4844  
Fig. 11. Display of all the segments of the LCD.  
To start the system-test:  
CAUTION  
The minimum off time for compressors is bypassed  
during the Installer System-Test. Equipment  
damage can occur if the compressor is cycled too  
quickly.  
Press and hold the increase ▲ and decrease ▲ keys at  
the same time, until two zeros appear. All segments of the  
LCD will be displayed before the two zeros appear. See  
Fig. 11 and 12.  
M6792  
TEST MODE NUMBER  
Fig. 12. Display of test number.  
Table 3. Tests Available In The Installer System-Test.  
Test  
Refer to Table 4 for the directions and results of the  
specific tests.  
Number  
Self-Test Description  
1
0-19  
0-39  
Heating equipment can be turned on  
and off  
NOTE: Press and hold the increase ▲ and decrease ▲  
keys together for three seconds to exit the  
system-test. The system-test will time out after  
ten minutes without any key presses.  
3
Cooling equipment can be turned on  
and off  
40-49  
60-69  
70-79  
Fan equipment can be turned on and off  
Keyboard keys test  
Thermostat information including date  
code and software versions are displayed  
Table 4. Installer System-Test Options.  
Key to  
Press  
Test  
Number  
Description  
Heating Equipment System-Test  
i
10  
11  
10  
Enter heating equipment system-test.  
▲
▲
Heat comes on. When Installer Setup number 02 is 01, the system fan is also energized.  
Heat and system fan turn off.  
Cooling Equipment System-Test  
i
30  
31  
30  
Change from heating to cooling equipment system-test.  
Cool and system fan come on.  
▲
▲
Cool and system fan turn off.  
Fan Equipment System-Test  
i
40  
41  
40  
Change from cooling to fan equipment system-test.  
▲
▲
Fan comes on.  
Fan turns off.  
(Continued)  
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T8501D DELUXE ZONE THERMOSTAT  
Table 4. Installer Self-Test Options (Continued).  
Description  
Key to  
Press  
Test  
Number  
Key Operation System-Test  
IMPORTANT  
Test numbers will only be displayed when the system is configured for the selected function.  
EXAMPLE: Numbers 60, 61 and 62 are the only numbers that will be displayed when a system  
is configured for heat only.  
System Key System-Test  
i
60  
61  
62  
63  
64  
Change from cooling or fan to key operation system-test.  
Heat Test Number is displayed.  
System  
System  
System  
System  
Off Test Number is displayed.  
Cool Test Number is displayed.  
Auto Test Number is displayed.  
Fan Key System-Test  
Fan  
Fan  
68  
69  
Fan on Test Number is displayed.  
Fan off Test Number is displayed.  
NOTE: Press and hold the increase ▲ and decrease ▲ keys together for three seconds to exit the system-test. The  
system-test will time out after ten minutes without any key presses.  
3.  
Press the increase ▲ key again to display the  
software identification code.  
THERMOSTAT INFORMATION  
1.  
Press the Information  
stat information.  
i
key to access the thermo-  
M4866  
4.  
Press the increase ▲ key again to display the  
software revision number (Example: 001=Revision  
number 1).  
M4864  
2.  
Press the increase ▲ key to display the production  
date code. The first two large digits are the month  
and the third digit is the last digit of the year (Example:  
027=February 1997).  
M6791  
M10444  
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T8501D DELUXE ZONE THERMOSTAT  
5.  
Press the increase ▲ key again to display the  
EEPROM identification code.  
CHECKOUT  
Outdoor Temperature Sensor  
(Where Applicable)  
Allow the outdoor temperature sensor to soak in the  
outdoor air for a minimum of five minutes before taking a  
reading. With an accurate thermometer (±1°F [±0.5°C]),  
measure the temperature at the sensor location, allowing  
time for the thermometer to stabilize before reading. Match  
the thermometer reading to the outdoor temperature  
display at the thermostat.  
M4867  
6.  
Press and hold the increase ▲ and decrease ▲  
keys together, until the room temperature is  
displayed, to exit the system-test. The system-test  
times out after ten minutes without any key presses.  
TROUBLESHOOTING GUIDE  
Symptom  
Possible Cause  
Action  
Display will not  
come on.  
Thermostat is not being  
powered.  
•
•
Check that C terminal is connected to the system transformer.  
Check for 24 Vac between C and R terminals.  
—
If missing 24 Vac:  
—
check if the circuit breaker is tripped—reset the  
circuit breaker.  
—
—
check if the system fuse is blown—replace the fuse.  
check if the power switch on the HVAC equipment is  
in the Off position—set to the On position.  
check wiring between thermostat and HVAC  
equipment—replace any broken wires and tighten  
any loose connections.  
—
—
If 24 Vac is present, proceed with troubleshooting.  
Thermostat microprocessor is Remove the thermostat from the wallplate for 2 minutes. After  
locked up.  
2 minutes, replace the thermostat on the wallplate.  
Temperature  
Room temperature display  
Enter Installer Setup number 37 and reconfigure the display.  
display is incorrect. has been reconfigured.  
Thermostat is configured for  
a
Enter Installer Setup number 14 and reconfigure the display.  
°
F or °C display.  
Bad thermostat location.  
Relocate the thermostat.  
The upper or lower  
temperature limits were  
reached.  
Check the temperature setpoints:  
Temperature  
•
•
Heating limits are 40 to 90°F (4.5 to 32°C)  
Cooling limits are 48 to 99°F (7 to 35°C).  
settings will not  
change. (Example:  
Cannot set the  
heating higher or  
the cooling lower.)  
The setpoint temperature  
range stops were configured. setpoint stops.  
Check Installer Setup numbers 34 and 35 and reconfigure the  
a
Available on select models.  
(Continued)  
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T8501D DELUXE ZONE THERMOSTAT  
Troubleshooting Guide (Continued).  
Symptom  
Possible Cause  
Action  
Heating will not  
come on.  
No power to the thermostat.  
•
•
Check that C terminal is connected to the system transformer.  
Check for 24 Vac between C and R and between R and W  
terminals.  
—
If missing 24 Vac:  
—
check if the circuit breaker is tripped—reset the  
circuit breaker.  
—
—
check if the system fuse is blown—replace the fuse.  
check if the system switch at the equipment is in the  
Off position—set to On position.  
—
check wiring between thermostat and HVAC  
equipment—replace any broken wires and tighten  
any loose connections.  
—
If 24 Vac is present, proceed with troubleshooting.  
Thermostat minimum off time Wait up to five minutes for the system to respond.  
is activated.  
System selection is not set to Set system selection to Heat.  
Heat.  
Cooling will not  
come on.  
No power to the thermostat.  
•
•
Check that C terminal is connected to the system transformer.  
Check for 24 Vac between C and R and between R and Y  
terminals.  
—
If missing 24 Vac:  
—
check if the circuit breaker is tripped—reset the  
circuit breaker.  
—
—
check if the system fuse is blown—replace the fuse.  
check if the system switch at the equipment is in the  
Off position—set to the On position.  
check wiring between thermostat and HVAC  
equipment—replace any broken wires and tighten  
any loose connections.  
—
—
If 24 Vac is present, proceed with troubleshooting.  
Thermostat minimum off time  
is activated.  
•
•
Wait up to five minutes for the system to respond.  
Enter Installer Setup number 33. Reconfigure minimum off  
time (if required).  
System selection is not set to Set system selection to Cool.  
Cool.  
Fan operation set for 00  
Enter Installer Setup number 02 and reconfigure the fan  
operation.  
System on indicator  
(
conventional heat) when it  
(
flame=heat,  
should be set for 01 (electric  
heat).  
snowflake=cool) is  
displayed, but no  
warm or cool air is  
coming from the  
registers.  
Conventional heating  
Wait a minute after seeing the On indicator and then check the  
registers.  
equipment turns on the fan  
when the furnace has  
warmed up to a setpoint.  
Heating equipment is not  
operating.  
Verify operation of heating equipment in self-test.  
System on indicator Option not activated.  
is not displayed,  
Enter Installer Setup number 36 and reconfigure to 00.  
but heating or  
cooling system is  
operating  
Outdoor  
temperature  
not displayed  
Option not activated.  
Enter Installer Setup number 24 and set to 01. Thermostat must  
have OT terminals and a C7089B1000 installed.  
a
Outdoor  
temperature  
display is incorrect  
Outdoor sensor is connected Refer to C7089B1000 installation instructions and check wiring  
incorrectly. between the thermostat and sensor.  
a
Wrong sensor.  
Replace sensor with C7089B1000 sensor.  
a
Available on select models.  
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®
Helping You Control Your World  
Honeywell Trol-A-Temp  
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Elmwood Park, NJ 07407-3204  
(
(
201) 794-8004  
800) 828-8367  
Fax: (201) 794-1359  
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