Honeywell T8112D Thermostat User Manual

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T8112D  
Programmable Thermostat  
PRODUCT DATA  
FEATURES  
HEAT-OFF-COOL System switch.  
AUTO-ON Fan switch.  
Separate programs for weekdays and weekends  
(5 day/2 day).  
Digital LCD display.  
Easy to program and install.  
Precise temperature control.  
Four daily energy saving programs.  
GENERAL  
Compatible with most 24 Vac standing pilot, gas  
electronic ignition, oil or central electric systems.  
The T8112D Programmable Thermostat provides energy  
savings for single-stage heating and cooling applications  
while providing reliable, precise temperature control.  
Requires two AA alkaline batteries.  
LCD flashes bAt Lo indicating low battery power.  
Isolated heating/cooling circuits.  
Contents  
General ...............................................................................  
Features ..............................................................................  
Specifications ......................................................................  
Ordering Information ...........................................................  
Installation ...........................................................................  
Programming the Thermostat .............................................  
Checkout and Settings ........................................................  
Troubleshooting ...................................................................  
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®
U.S. Registered Trademark  
Copyright © 1998 Honeywell Inc.  
All Rights Reserved  
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T8112D PROGRAMMABLE THERMOSTAT  
Mounting:  
SPECIFICATIONS  
Mounts on mounting plate directly on wall. Mounting screws  
and wall anchors provided.  
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.  
Setpoint Range:  
45°F to 88°F (7°C to 31°C).  
Operating Ambient Temperature Range:  
0°F to 110°F (4°C to 43°C).  
4
Shipping Temperature Range:  
20°F to 120°F (-29°C to -49°C).  
-
Model:  
T8112D Thermostat: Provides electronic programmable  
control for 24 to 30 Vac heating and cooling systems.  
Temperature Display:  
Fixed or field selectable.  
Programming Keys:  
Eight program keys.  
Operating Relative Humidity:  
5
to 90 percent RH; noncondensing.  
Electrical Rating:  
Battery operated (2 AA alkaline batteries).  
Time Indication:  
2 hour with AM, PM indication.  
1
System and Fan Ratings:  
Cycles Per Hour Adjustment:  
1.2A run; 7.5A inrush.  
Heating: Field adjustable to 3, 6, or 9 cph ±10 percent.  
Cooling: Factory set at 3 cph ±10 percent (not field  
adjustable).  
Total cooling and fan load not to exceed 1.2A.  
Dimensions:  
See Fig. 1.  
Calibration:  
Thermostat and thermometer self-calibrating to ±1.25°F.  
6-7/8 (175)  
1(25)  
3/4 (19)  
1
(
-1/4  
32)  
4
102)  
(
M9349  
Fig. 1.T8112 dimensions in in. (mm).  
ORDERING INFORMATION  
When purchasing replacement and modernization products from your TRADELINE® wholesaler or your distributor, refer to the  
TRADELINE® Catalog or price sheets for complete ordering information, or specify:  
1
. Model Number.  
2. Accessories, as desired.  
If you have additional questions, need further information, or would like to comment on our products or services, please write or  
phone:  
1
2
. Your local Honeywell Home and Building Control Sales Office (check white pages of phone directory).  
. Home and Building Control Customer Relations  
Honeywell, 1885 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.  
68-0206  
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T8112D PROGRAMMABLE THERMOSTAT  
Mounting Plate Installation (Fig. 2)  
INSTALLATION  
1
. Hold mounting plate in position and mark the two holes  
for mounting.  
When Installing this Product…  
2. Level for appearance only; thermostat functions  
properly even when not level.  
1
. Read these instructions carefully. Failure to follow the  
instructions can damage the product or cause a  
hazardous condition.  
3. Tighten the mounting screws.  
4. Set aside the mounting plate.  
2
. Check the ratings given in the instructions and on the  
product and in the compatibility chart (Table 1) to make  
sure the product is suitable for your application.  
. Installer must be a trained, experienced service  
technician.  
5. Drill the two holes in the wall as marked.  
Drill 3/16 in. holes for drywall.  
Drill 7/32 in. holes for plaster or wood.  
3
4
6. Reposition the mounting plate over the holes and pull  
wires through the wiring opening.  
7. Loosely insert the two mounting screws into the holes.  
. After installation is complete, check out product  
operation as provided in these instructions.  
WALL ANCHORS (2)  
Compatibility  
WIRES THROUGH  
WALL OPENING  
Check Table 1 to make sure the thermostat is compatible with  
the intended system.  
WALL  
Table 1. Compatibility Chart.  
Compatible  
with T8112D  
System Type  
Gas—Standing Pilot  
Yes  
MOUNTING  
PLATE  
Gas—Electronic Ignition  
Gas-Fired Boilers  
Yes  
Yesa  
MOUNTING  
SCREWS (2)  
Gas—Millivolt  
No  
M1718  
Oil-Fired Boilers  
Yesa  
Yes  
Fig. 2. Mounting plate installation.  
Oil-Fired Furnace  
Electric Furnace  
Yes  
Wiring Thermostat  
All wiring must comply with local electrical codes and  
ordinances. Refer to Fig. 5 through 8 for typical hookups. A  
letter code is located near each terminal for identification.  
Electric Air Conditioning  
Baseboard Electric (120/240 Line Volt)  
Heat pumps/Multistage Equipment  
Yes  
No  
No  
a
1. Connect the system wires to the thermostat. See Fig. 3.  
A letter code is located near each terminal for  
identification.  
Compatible with 2-wire Honeywell zone valves.  
All system types:  
Not compatible with any 120/240 volt circuit.  
Not designed for steam or gravity systems.  
Not compatible with 2-wire White Rodgers no. 1361 zone  
valves.  
NOTE: Hold the thermostat as shown in Fig. 4 to  
minimize the need for wire extenders.  
Isolating relay required for 3-wire thermostats for zone valves.  
2
3
4
. Securely tighten each terminal screw.  
. Push excess wire back into the hole.  
. Plug the hole with nonflammable insulation to prevent  
drafts from affecting thermostat operation.  
. Run the required number of wires to the thermostat  
location. Refer to Fig. 5 through 8 for typical wiring  
diagrams.  
CAUTION  
5
6
Damage to Heating Cooling System Possible.  
Be careful when handling wires during installation.  
Disconnect power at furnace or main breaker/fuse box.  
. In 5-wire installations only, be sure to remove the factory-  
installed jumper connecting the terminals R and Rc.  
Location  
Locate the thermostat about 5 ft (1.5m) above the floor in  
an area with good air circulation at average temperature.  
Do not mount the thermostat where it can be affected by:  
drafts or dead spots behind doors and in corners.  
hot or cold air ducts.  
concealed pipes and chimneys.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
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T8112D PROGRAMMABLE THERMOSTAT  
JUMPER (FACTORY-  
INSTALLED) REMOVE  
IF 5-WIRE SYSTEM  
3-WIRE COOL-ONLY (JUMPER INTACT)  
INSERT  
STRAIGHT  
UNDER  
SCREW HEAD  
A
C
5
/16 in.  
(8 mm)  
c
R
R
STRIP  
B
D
W
R
Y
G
JUMPER  
END OF WIRE  
VISIBLE HERE  
Rc  
G
W
Y
M1712A  
Fig. 3. Proper wiring technique.  
COOLING  
CONTACTOR  
COIL  
FAN  
RELAY  
L1  
(
HOT)  
L2  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M848A  
Fig. 6. 3-wire cool-only application (jumper intact).  
4-WIRE HEAT/COOL (JUMPER INTACT)  
A
C
B
D
W
R
Y
G
JUMPER  
M3002A  
Fig. 4. Holding thermostat while installing.  
Rc  
2
-WIRE HEAT-ONLY (JUMPER INTACT)  
HEATING  
RELAY OR  
VALVE COIL  
COOLING  
CONTACTOR  
COIL  
A
C
B
D
FAN  
RELAY  
L1  
(HOT)  
L2  
JUMPER  
W
R
Y
G
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
Rc  
M1710B  
Fig. 7. 4-wire heat/cool application (jumper intact).  
HEATING  
RELAY OR  
VALVE COIL  
L1  
(
HOT)  
1
L2  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M1709B  
Fig. 5. 2-wire heat-only application (jumper intact).  
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T8112D PROGRAMMABLE THERMOSTAT  
5
-WIRE HEAT/COOL (JUMPER REMOVED)  
NOTE: This thermostat does not have a setting for steam/  
gravity air. Cycles would not be long enough for  
accurate temperature control.  
A
C
B
D
NOTE: For condensing furnaces, follow manufacturer  
instructions.  
W
R
Y
G
IMPORTANT  
When using a high efficiency furnace such as a  
Rc  
90 percent or greater AFUE (Average Fuel Utilization  
Efficiency) unit, adjust screw A out one turn and  
screw B In one turn.  
HEATING  
RELAY OR  
VALVE COIL  
FAN  
RELAY  
If you want a longer on-time, readjust screws A and B as  
follows (refer to Table 1 Compatibility Chart):  
COOLING  
CONTACTOR  
COIL  
Warm Air Furnace—set at the Hot Water setting (A—out  
one turn, B—in).  
Electric Furnace—leave at the Warm Air Furnace setting  
A—in, B—in).  
1
1
L1  
L1  
(HOT)  
(HOT)  
(
L2  
L2  
NOTE: This thermostat does not have a setting for steam/  
gravity air. Cycles would not be long enough for  
accurate temperature control.  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M1711B  
Fig. 8. 5-wire heat/cool application (jumper removed).  
Install Batteries  
Adjust Fan Operation Switch, as Required  
IMPORTANT  
The thermostat fan operation switch, labeled FUEL SWITCH  
Batteries must be installed for programming and  
operating the thermostat and heating/cooling  
system.  
(
see Fig. 9) is factory set in the F position. This is the correct  
setting for most systems. If you have an electric heat system,  
set the switch to E. In systems with the G terminal connected,  
the E setting turns on the fan immediately with heating or  
cooling.  
1
. Use two AA alkaline batteries; nonalkaline batteries will  
not last as long.  
2
3
4
. Make sure the thermostat is set to the Off position.  
. Use a coin to remove the battery door (see Fig. 10).  
. Install the new batteries as shown, making sure positive  
and negative terminals are oriented correctly (see Fig. 11).  
. Replace the battery door.  
THERMOSTAT BACK  
A
B
C
ADJUST SCREWS THROUGH HOLES  
TO SELECT OPERATION DESIRED  
5
FUEL SWITCH  
POSITION  
HEATING SYSTEM  
WARM AIR  
FURNACE  
A–IN  
B–IN  
F
D
When the batteries are running low, a bAt Lo indicator will  
flash for one to two months before batteries run out  
completely. Replace the batteries as soon as possible after  
the indicator starts flashing. If the batteries are not replaced  
when the bAt Lo indicator is flashing, the indicator eventually  
stops flashing. When the batteries are almost completely  
dead, bAt Lo will stay on without flashing, indicating that the  
thermostat and heating/cooling system have stopped working.  
The thermostat will not function after the batteries are  
completely dead, and the bAt Lo indicator disappears, leaving  
a completely blank display.  
HOT WATER A–OUT B–IN  
F
BOILER  
1 TURN  
A–IN  
ELECTRIC  
FURNACE  
B–OUT  
1 TURN  
E
FOR HIGH EFFICIENCY FURNACE (90%+ AFUE)  
W
Y
G
ADJUST: SCREW A–OUT 1 TURN  
SCREW B–IN  
FUEL SWITCH – F POSITION  
FUEL SWITCH  
F
E
R
Rc  
M3669  
Fig. 9. Back view of thermostat.  
To remove the batteries, press down on the left ends. When  
the new batteries are installed within 20 to 30 seconds of  
removing the old ones, the thermostat does not have to be  
reprogrammed. If the display is blank, the batteries are dead  
or incorrectly installed and the thermostat has to be  
reprogrammed. See Owner’s Manual for reprogramming  
instructions.  
Adjust System On-Time as Required  
The thermostat on-time is factory set for a warm air, gas or oil  
heating system. If you are installing it on another type of  
system, the system on-time must be adjusted by changing the  
setting of screws A and B on the back of the thermostat. Use  
the heating system table in Fig. 9 as a guide to minimize room  
temperature swings. The system on-time should be optimized  
according to the type of system. Setting the screw out one  
turn means turning the screw approximately 360°, or one  
complete turn.  
IMPORTANT  
Although the thermostat has a low battery indicator,  
replace the batteries once a year to prevent the  
thermostat from losing time and programming due to  
lack of battery power.  
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T8112D PROGRAMMABLE THERMOSTAT  
PROGRAMMING THE THERMOSTAT  
Set the Current Time/Day  
To set the time:  
1
2
. Press and release the Clock/Day key once.  
. Press the Time keys  or  until the current time  
displays.  
To set the day:  
M5781  
1. Press and release the Clock/Day key again.  
2
. Press the Time keys  or  until the current day  
Fig. 10. Removing battery door.  
displays.  
3. Press the Run Program key.  
INSTALL TWO AA ALKALINE  
BATTERIES AS SHOWN  
Heating Program  
To set the system switch to HEAT:  
AM  
TU  
1. Press and release the Schedule key once. WAKE,  
Mon-Fri , and SET appear on the display.  
LEAVE  
2
. Press the Time keys  or  to program WAKE time,  
and Temp keys  or  to program WAKE temperature  
for Mon-Fri.  
3
4
5
. Repeat this sequence for LEAVE, RETURN, and  
SLEEP.  
Fan Auto On  
System Cool Off Heat  
. Press the Schedule key until SAT, SUN, WAKE and  
SET appear on the display.  
. Press the Time keys  or  to program WAKE time,  
and Temp  or  to program WAKE temperature for  
Sat-Sun.  
FAN SWITCH  
SYSTEM  
SWITCH  
M5782  
Fig. 11. Installing batteries.  
6. Repeat this sequence for SLEEP.  
Mounting Thermostat  
Cooling Program  
1
. Engage the tabs at the top of the thermostat and  
mounting plate. See Fig. 12.  
1
2
3
. Set the system switch to COOL and follow the same  
procedure as for the Heating Program.  
. After programming, adjust the fan and system switches  
as desired.  
2. Press the lower edge of the case to latch.  
NOTE: To remove the thermostat from the wall, first pull out  
the bottom of the thermostat and then remove the  
top portion.  
. Press and release the Run Program key to start the  
program.  
A Quick Guide for Operating or Making  
Changes  
A. ENGAGE TABS AT TOP OF  
B. PRESS LOWER EDGE  
THERMOSTAT AND MOUNTING PLATE.  
OF CASE TO LATCH.  
NOTE: The system switch must be set to Heat or Cool to  
perform the following.  
AM  
TULEAVE  
To temporarily change the temperature for the  
current period only:  
1
. Press the Temp keys  or .  
The temporary indicator shows on the display and  
cancels itself at the next scheduled change.  
. To cancel sooner, press the Run Program key.  
2
M5780  
To hold a temperature indefinitely:  
. Press the Hold Temp key.  
. Press the Temp keys  or .  
. To cancel, press the Run Program key.  
1
2
3
Fig. 12. Mounting thermostat on mounting plate.  
68-0206  
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T8112D PROGRAMMABLE THERMOSTAT  
To check the current temperature setting:  
Fan Switch  
Press the Run Program key. (When using TEMPORARILY  
CHANGE or HOLD, pressing this key will cancel the change  
or hold.)  
Auto  
Auto  
On  
FAN AUTO: Normal setting for most homes. A  
single-speed fan turns on automatically with  
the air conditioner or furnace. A two-speed fan  
usually runs on high with the air conditioner  
and on low with the furnace.  
M1705  
To check the programs:  
On  
FAN ON: The fan runs continuously. Use for  
improved air circulation during special  
occasions or for more efficient electronic air  
cleaning.  
1. Press the Schedule key repeatedly to see each time  
and temperature.  
M1706  
2. Press the Run Program key.  
To cancel a program:  
System Switch  
1
. Press the Schedule key until the program to cancel  
appears  
COOL: The thermostat controls the air  
conditioning system.  
Cool  
Off  
Heat  
2. Press both the Time keys  and  together.  
M1704  
To permanently change a program:  
OFF: Both the heating and air conditioning  
systems are off.  
Cool  
Cool  
Off  
Off  
Heat  
Repeat the steps in the Heating Program or Cooling Program  
section as applicable.  
M1707  
To return to the normal program:  
Press the Run Program key.  
HEAT: The thermostat controls the heating  
system.  
Heat  
M1703  
CHECKOUT AND SETTINGS  
After the thermostat is mounted on the mounting plate, check operation as follows:  
Heating  
Cool  
Off  
Heat  
Do not check the heating system operation by jumpering the thermostat terminals at the primary control  
such as the gas valve, zone valve, or oil burner control. This will damage the thermostat.  
M1703  
Auto  
On  
Move the system switch to HEAT and the fan switch to AUTO.  
M1705  
Temp  
Press the TEMP key until the setting is about 10°F (6°C) above the room temperature. After a short  
delay, the heating should start and the fan should run (immediately if fan operation switch is set in  
E position).  
Temp  
Press the TEMP key until the setting is about 10°F (6°C) below the room temperature. The heating  
equipment should shut off.  
Cooling  
Cool  
Off  
Heat  
To avoid possible compressor damage, do not operate the cooling system when the outside temperature  
is below 50°F (10°C). See the compressor manufacturer instructions for further information.  
M1704  
NOTE: When the cooling setting is changed, the thermostat can delay up to five minutes before turning  
on the air conditioner to protect the compressor.  
Auto  
On  
Move the system switch to COOL and the fan switch to AUTO.  
M1705  
Temp  
Press the TEMP key until the setting is about 10°F (6°C) below room temperature. The cooling  
equipment and fan should start.  
Temp  
Off  
Press the TEMP key until the setting is about 10°F (6°C) above the room temperature. The cooling  
equipment and fan should stop.  
Move the system switch to OFF with the fan switch remaining at AUTO. The system and fan should be  
off.  
Cool  
Heat  
M1707  
Auto  
On  
M1705  
68-0206  
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T8112D PROGRAMMABLE THERMOSTAT  
Minimum Off-Timer  
A minimum off-timer for the T8112D assures that the cooling  
compressor does not come on again for at least five minutes  
after it turns off. The minimum-off timer is triggered when the  
compressor turns off and when the system switch is changed.  
If the compressor turns off when the setpoint is changed, then  
the minimum-off timer is triggered, which operates only during  
the cooling cycle of the T8112D.  
TROUBLESHOOTING  
IF…  
THEN…  
Display will not come on.  
• Set the system switch to OFF; remove batteries; insert backward for at least  
five seconds to reset thermostat; replace batteries correctly. Display should come  
on.  
Make sure batteries are fresh and installed correctly.  
Temperature display will not go lower • The temperature setting limit has been reached. The setting range is 45°F to 88°F  
than 45°F (7°C) or higher than 88°F  
31°C) during programming.  
(7°C to 31°C).  
(
Heating will not come on.  
• If the display is blank or displays bAt Lo, install fresh batteries.  
Check that the switch on the thermostat is set to HEAT.  
Check the system fuse or circuit breaker and replace or reset if necessary.  
If the temperature setting is higher than the current temperature, and SYSTEM ON  
indicator is lit, see the furnace manufacturer instructions.  
Cooling will not come on.  
• If the display is blank or displays bAt Lo, install fresh batteries.  
In 2- or 4-wire installations, verify that the R-Rc jumper is installed.  
Check that the switch on the thermostat is set to COOL.  
Check the system fuse or circuit breaker and replace or reset if necessary.  
The thermostat has a built-in time delay on cooling. Allow five to ten minutes after  
changing the setting before the air conditioner starts.  
If the temperature setting is lower than the current temperature, and the SYSTEM  
ON indicator is lit, see the air conditioner manufacturer instructions.  
SYSTEM ON indicator is lit, but no  
heat is coming from the registers.  
• Allow time for the furnace to heat up and the fan to come on before checking for  
heat at the register. Check to make sure system on-time is set correctly according  
to the instructions in the Installation section.  
Furnace or air conditioner cycles too  
frequently.  
• Readjust according to the instructions in the Installation Section.  
The system on-time is too short or too • Readjust according to the instructions in the Installation Section.  
long.  
The thermostat current setting does  
not match the display temperature.  
• Check that the wiring hole in the wall behind the wallplate was plugged with  
insulation to prevent drafts that could adversely affect thermostat operation.  
It is normal for the current setting and display temperature to differ occasionally.  
bAt Lo remains on the display after  
fresh batteries have been installed.  
• Remove batteries. Wait one hour. Install fresh alkaline batteries.  
Home and Building Control  
Honeywell Inc.  
Home and Building Control  
Honeywell Limited-Honeywell Limitée  
155 Gordon Baker Road  
North York, Ontario  
1
985 Douglas Drive North  
Golden Valley, MN 55422  
M2H 3N7  
Printed on recycled paper containing at  
least 10% post-consumer paper fibers.  
68-0206 L.C. 2-98 Printed in U.S.A.  
www.honeywell.com/yourhome  

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