Honeywell T841A Thermostat User Manual

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T841A,B Easy-To-See™  
Heat Pump Thermostat  
TRADELINE®  
INSTALLATION INSTRUCTIONS  
APPLICATION  
MERCURY NOTICE  
The T841A, B Easy-to-See™ Heat Pump Thermostat  
provides 24 Vac control of 2-stage heating and 1-stage  
cooling in heat pump systems, using manual change-  
over.  
This control contains mercury in a sealed tube.  
Do not place the control in the trash at the end of  
its useful life. If this control is replacing a control  
that contains mercury in a sealed tube, do not  
place your old control in the trash.  
The T841A Thermostat provides EM. HT.-HEAT-OFF-  
COOL System switching and AUTO-ON Fan switching.  
The T841B Thermostat provides HEAT-OFF-COOL  
System switching and AUTO-ON Fan switching.  
Contract your local waste management authority  
for instructions regarding recycling and the  
proper disposal of this control, or of an old control  
containing mercury in a sealed tube.  
The side of the thermostat features raised numbers for  
easy temperature setting by touch or sight. An audible  
click is heard with indents every two degrees as the  
temperature setpoint lever is moved. The thermostat  
wallplate features raised letters to aid in setting System  
switch and Fan switch settings. See Fig. 1.  
INSTALLATION  
When Installing this Product...  
1
.
Read these instructions carefully. Failure to follow  
them could damage the product or cause a hazard-  
ous condition.  
The T841A,B includes a thermostat and wallplate.  
Test holes are provided on the front of the thermostat to  
accommodate test meter probes without removing the  
thermostat from the wall. Remove the cover of the  
thermostat to expose the test holes that are labeled to  
correspond with the terminals on the thermostat back.  
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 technician.  
After installation is complete, check out product  
operation as provided in these instructions.  
4
OPERATION  
CAUTION  
The stages of heat make sequentially as the temperature  
drops. Make refers to the mercury switch initiating a call  
for heat or cool.  
Electrical Hazard.  
Can cause Disconnect electrical shock or  
equipment damage.  
There is about 1°F (0.6°C) between stages so the  
second stage (auxiliary heat) makes only when the first  
stage cannot handle the load. This °F is the interstage  
differential.  
Disconnect power before beginning installation.  
IMPORTANT  
— To prevent interference with the thermostat link-  
age, keep wire length to a minimum and run  
wires as close as possible to the thermostat  
base.  
For T841A Thermostat only (not for T841B Thermostat):  
light emitting diode (LED) indicators light when  
something specific happens within the system:  
When AUX. HT. green or amber LED lights, auxiliary  
heat (second stage heat) is operating because the  
weather is so cold, the heat pump alone cannot  
handle the load.  
— Do not short across coil terminals on the relay.  
This can burn out thermostat heat anticipator.  
— Never install more than one wire per terminal  
unless a factory-supplied jumper with a spade  
terminal is used.  
When red EM. HT. LED lights, emergency heat is  
operating (electric strip heaters), because home-  
owner physically switched to EM. HT. position. See  
heating/cooling manufacturer instructions.  
®
U.S. Registered Trademark  
Copyright © 2003 Honeywell International Inc. •  
• All Rights Reserved  
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HEAT PUMP THERMOSTAT  
Location  
Wiring  
Locate the thermostat between 4 ft (1.2m) and 5 ft (1.5m)  
above the floor in an area with good air circulation at  
average room temperature.  
All wiring must comply with local codes and ordinances.  
Follow equipment manufacturer wiring instructions when  
available.  
NOTE: Because of height restrictions of some disabled  
users, it may be necessary to lower the thermo-  
stat location to 4 ft (1.2m) above the floor.  
NOTE: Four screws are provided with the thermostat;  
only two are required for mounting.  
1
.
Run wiring (if necessary) to the location. If wiring is  
plastered into the wall, make a hole next to the wire  
and loosen the wires so they can be pushed back  
into the wall later.  
Do not install thermostat where it can be affected by:  
drafts, or dead spots behind doors and in corners.  
hot or cold air from ducts.  
radiant heat from sun, appliances or fireplaces.  
concealed pipes and chimneys.  
2. Thread the wires through the hole.  
3. Pull the wires through the entrance hole on the  
wallplate.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
4. Connect the wires to the terminals on the back of  
the thermostat. See Fig. 1-3.  
5.  
Push the excess wire back through the hole and  
plug any openings with packing material to prevent  
drafts that can affect thermostat performance.  
Use two of the four screws provided to loosely  
secure the thermostat and the wallplate to the wall  
or outlet box through the two middle mounting  
holes. See Fig. 1.  
This thermostat is a precision instrument and was  
carefully adjusted at the factory. Handle it carefully.  
6.  
Mounting  
The T841A,B can be mounted directly on a wall or a  
horizontal outlet box. Choose the method that best fits  
your installation. In replacement applications, check the  
existing thermostat wires for cracked or frayed insulation.  
Replace any wires in poor condition.  
NOTE: The sheet metal screws included with the ther-  
mostat are designed for use in plaster walls that  
do not need anchors.  
To remove the thermostat cover:  
IMPORTANT  
1.  
2.  
3.  
Grasp thermostat cover at the top and bottom with  
one hand.  
An incorrectly leveled thermostat causes inac-  
curate temperature control.  
Pull outward on the bottom edge of the cover until  
it snaps free of the thermostat base.  
Carefully remove and save the packing material  
surrounding the mercury switches.  
7. Exactly level the thermostat using a spirit level or  
plumb line.  
8. Tighten the screws in the middle mounting holes.  
9.  
Replace the thermostat cover.  
WALLPLATE  
T841 BASE  
TEMPERATURE  
SETPOINT LEVER  
A
O
SETPOINT  
SCALE  
MOUNTING  
SCREWS (2)  
EH  
H O C  
AUX. HEAT  
LED  
EM. HEAT  
LED  
AUTO ON  
FAN  
8
0
0
7
EM. HEAT HEAT OFF COOL  
FAN SWITCH  
60  
50  
SYSTEM SWITCH  
BACK OF DEVICE  
HEAT PUMP THERMOSTAT  
T841 COVER  
WIRING TERMINAL  
UP TO 12)  
(
M11427  
MOUNTING  
HOLES (4)  
Fig. 1. Mounting thermostat to wallplate (T841A model shown).  
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HEAT PUMP THERMOSTAT  
L1  
(HOT) L2  
1
CHANGEOVER  
RELAY (COOL)  
O
L
H1  
FALL  
FAN SWITCH  
AUTO  
C1  
SYSTEM  
MONITOR  
EM. HT.  
LED (RED)  
3
FAN RELAY  
G
R
E
H1 ANTICIPATOR  
C1 ANTICIPATOR  
ON  
4
EM. HT.  
RELAY  
X
AUX. HT.  
LED (GREEN)  
W2  
SYSTEM  
SWITCH  
FALL  
AUX. HT.  
RELAY  
B
H2  
EM. HT.  
HEAT  
CHANGEOVER  
RELAY (HEAT)  
W1  
Y1  
OFF  
2
JUMPER  
HEAT RELAY 1  
COOL  
H2 ANTICIPATOR  
COMPRESSOR  
CONTACTOR  
1
2
3
4
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
REMOVE W1-Y1 JUMPER WHEN HEAT RELAY 1 IS USED.  
WHEN L TERMINAL IS CONNECTED TO SYSTEM MONITOR, EM. HEAT LED ALSO INDICATES COMPRESSOR MALFUNCTION.  
X TERMINAL MUST BE CONNECTED FOR PROPER OPERATION.  
M1103E  
Fig. 2. Internal schematic and typical wiring diagram for T841A with AUX. HT. and EM. HT. LEDs. Provides heat  
or cool changeover relay control and automatic fan in emergency heat mode.  
W1  
H1/C1  
ANTICIPATOR  
HEAT RELAY 1  
HEAT RELAY 2  
W2  
H1  
C1  
FALL  
B
HEAT CHANGEOVER  
VALVE  
FAN SWITCH  
AUTO  
G
ON  
FAN RELAY  
L1  
R
X
(HOT)  
SYSTEM  
SWITCH  
L2  
1
HEAT  
OFF  
H2 ANTICIPATOR  
H2  
Y1  
COOL  
FALL  
COMPRESSOR  
CONTACTOR  
O
COOL CHANGEOVER VALVE  
M6068A  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
Fig. 3. Internal schematic and typical wiring diagram for T841B 2-stage heat, 1-stage cool, manual changeover.  
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HEAT PUMP THERMOSTAT  
SETTINGS  
CHECKOUT  
Temperature Setting  
Heating  
The enlarged, raised numbers on the right edge of the  
thermostat can be used for easy temperature setting by  
touch or sight while moving the temperature setpoint  
lever to the desired temperature setting. The large 5, 6, 7  
and 8 refer to 50°F (10°C), 60°F (16°C), 70°F (21°C) and  
Move the System switch on the thermostat to HEAT and  
the Fan switch to AUTO. Move the temperature setpoint  
lever to about 10°F (6°C) above the room temperature.  
Heating should start and the fan should run. Move the  
setpoint lever about 10°F (6°C) below the room  
8
0°F (27°C), respectively. A click is heard with indents  
temperature. Heating and fan should shut off.  
every two degrees as the temperature setpoint lever is  
moved. See Fig. 1.  
IMPORTANT  
To prevent compressor short cycling, a mini-  
mum-off timer can be included to prevent the  
compressor from starting for up to five minutes  
from when the thermostat last turned off the  
compressor, or from when the system first  
received power.  
System Switch Setting  
The enlarged, raised letters on the left bottom edge of the  
wallplate can be used for easy recognition of System  
switch settings:  
For the T841A Thermostat: The large EH, H, O and C  
refer to EM. HT., HEAT, OFF and COOL.  
For the T841B Thermostat: The large H, O and C refer  
to EM. HT., HEAT, OFF and COOL.  
Cooling  
The System switch settings control the system operation  
as follows:  
CAUTION  
Compressor Damage Hazard.  
Operating cooling equipment in cold weather  
can damage compressor.  
EM.HT (only on T841A): Emergency heat relay is  
energized. Cooling system is off. Compressor is  
de-energized. Fan runs on call for heat if the Fan  
switch is in the AUTO position. EM. HT. LED is on.  
HEAT: Heating system is automatically controlled by  
the thermostat. Cooling system is off.  
Do not operate air conditioner if outdoor  
temperature is below 50°F (10°C).  
Move the System switch on the thermostat to COOL and  
the Fan switch to AUTO. Move the temperature setpoint  
lever about 10°F (6°C) below the room temperature.  
Cooling and fan should start (see Note in Checkout  
section). Move the setpoint lever about 10°F (6°C) above  
the room temperature. Cooling and fan should shut off.  
OFF: Both the heating and cooling systems are off. If  
the fan is set to the AUTO position, the cooling fan  
is also off.  
COOL: Cooling system is automatically controlled by  
the thermostat. Heating system is off.  
Fan Switch Setting  
Fan  
On theT841A,B, large A, O raised letters on the right  
bottom edge of the wallplate refer to AUTO and ON fan  
settings. The Fan switch settings control the fan as  
follows:  
Move System switch to OFF, and Fan switch to ON. The  
fan should run continuously. Move Fan switch to AUTO.  
In this position, the fan operates in response to the  
thermostat in both heating and cooling.  
AUTO: Fan operates in response to thermostat in both  
heating and cooling.  
ON: Fan operates continuously.  
Automation and Control Solutions  
Honeywell International Inc.  
Honeywell Limited-Honeywell Limitée  
35 Dynamic Drive  
Scarborough, Ontario  
M1V 4Z9  
1
985 Douglas Drive North  
Golden Valley, MN 55422  
Printed in U.S.A. on recycled  
paper containing at least 10%  
post-consumer paper fibers.  
69-1043-2 G.H. Rev. 3-03  
www.honeywell.com/yourhome  

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