Emerson Sensi ST75 User manual

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PRO Installation
Touch Wi-Fi
Thermostat

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Designed by the pros for the pros
There are a lot of choices when it comes to buying a thermostat,
but only one combines 125 years of experience and the latest
connected home technology to empower your customers
to take control of their comfort from anywhere. We proudly
connect you to a professional-grade thermostat that you
can offer your customers with confidence and that will keep
you connected with them even after the initial install.
Sensi partner program
Always be the Contractor-On-Call with your customers.
The Sensi app saves your contact information so when your
customer needs service, you’re just a tap away. Register at
www.sensiregistration.com.
Need help?
Visit sensicomfort.com/support for around-the-clock
access to support articles, instructional downloads
and comprehensive support videos. Our highly-trained
Sensi Support Team is available seven days a week.
1.888.605.7131
[e-mail]

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Easy to install and connect
Sensi is designed to install like a standard thermostat. It
gives you the flexibility to connect to Wi-Fi at installation
or let your customer connect it later using the Sensi app.
MOBILE DEVICE COMPATIBILITY
OPERATING SYSTEM COMPATIBILITY
iOS Yes
Android Yes
Amazon Fire Yes
SMART HOME PLATFORM COMPATIBILITY
OPERATING SYSTEM COMPATIBILITY
Wink Yes
Amazon Alexa Yes
Apple HomeKit Yes

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HVAC SYSTEM COMPATIBILITY
SYSTEM TYPE COMPATIBILITY MODIFICATIONS
Conventional heating and
cooling
•Gas furnace
•Air conditioner
•Electric furnace
•Boiler
Yes Requires a common
wire (c-wire)
Heat only
•Gas furnace
•Electric furnace
•Boiler
Yes Requires a common
wire (c-wire)
Cool only
•Air conditioner Yes Requires a common wire (c-wire)
Heat pump Yes Requires a common
wire (c-wire)
Communicating
proprietary systems No Needs standard HVAC wiring
Line voltage No Requires low voltage
(20-30VAC)
Millivolt systems No Requires 20-30VAC

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What’s in the box?
•Sensi Thermostat
•Screws and Anchors
•Wire Labels
•Sensi Security Code
(found on the back of the Welcome Guide)
Items needed for Wi-Fi connection:
•The homeowners compatible iOS or Android
•Device with the Sensi app installed and registered
•Your customer’s Wi-Fi network name (SSID) and password
QUICK TIP: Ask the homeowner to download the
Sensi app and gather their Wi-Fi information
while you are installing the thermostat.

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Installation
1. Install Sensi thermostat, referring to these terminal
definitions, cross references and wiring diagrams as needed:
OLD
THERMOSTAT
SENSI
THERMOSTAT
CONVENTIONAL
SYSTEM
HEAT PUMP
SYSTEM
RH RH* Power for heating, 24V
RC, R RC* Power for cooling, 24V
C, X, B** C Common wire, 24V
Y, Y1 Y 1st stage cool 1st outdoor
stage heat
Y2 Y2/* 2nd stage cool 2nd outdoor stage
heat and cool
W, W1, W/E,
Aux/E, E W/E 1st indoor stage heat 1st stage axillary/ emergency heat
W2*** W2 2nd indoor
stage heat 2nd stage axillary/ emergency heat
G G Indoor blower (fan)
O,B,** O/B O/B Changeover (reversing valve) connection
for heat pump or zone panel systems
L L no function “L” terminal
connection
* Two transformer systems (separate RC and RH wires), clip jumper located
on backplate to the right of the terminals.
** Label “B” as “C” only if the old thermostat also had a wire in “O”. If there is no wire
on “O”-label the wire “B”.
*** On Heat Pump system with separate W2 and E wires, label both wires W/E
(2 wires in one terminal).

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SINGLE STAGE OR MULTI-STAGE SYSTEM NO HEAT PUMP) WITH TWO TRANSFORMERS
System Configuration
Thermostat
*
*Two transformers systems (separate RC and RH wires), clip internal RC/RH jumper, located on back of thermostat.
HOT
120 VAC
NEUTRAL
HOT 120 VAC NEUTRAL
NEUTRAL 24 VAC HOT
NEUTRAL
24 VAC
HOT
Cooling Transformer
Heating Transformer
Dots Indicate
Phased
Relationship
Dots Indicate
Phased
Relationship
Single
Stage
AC1
GA1
EL1
24 Volt
(Hot)
Cool
24 Volt
(Hot)
Heat
24 Volt
(Common)
Cool
Mode
1st stage
Blower Circulator Fan Energized On Call For Cool (And Heat If Confi- gured For Electric Heat)
O
Energized
Constantly
in Cool
Mode
(Factory
Default)
B
Energized
Constantly
In Heat
Mode (Or
Aux Mode)
Heat
Mode
1st Stage
Heat
Pump “L”
Terminal
Connection
Cool
Mode
2nd Stage
No
Output
Heat
Mode
2nd Stage
No
Output
Multi-
Stage
AC2
GA2
EL2

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HEAT PUMP SYSTEMS
System Configuration
Thermostat
*
**
*Internal jumper between RC and RH, located on back of thermostat.
**Common connection required on Heat-only, Cool-only or Heat Pump systems.
HOT 120 VAC NEUTRAL
NEUTRAL
24 VAC
HOT
Dots Indicate
Phased
Relationship
Single
Stage
Heat
Pump
HP1 24 Volt
(Hot)
Cool
24 Volt
(Hot)
Heat
24 Volt
(Common)
Heat And
Cool Mode
1st Stage
(Com-
pressor)
NOTE: Dual
Fuel Option
De-Energizes
Heat Mode
1st Stage
Blower/ Circulator Fan Energized On Call For Cool (And Heat If Configured For Electric Heat)
O
Energized
Constantly
in Cool
Mode
(Factory
Default)
B
Energized
Constantly
In Heat
Mode (Or
Aux Mode)
Heat
Mode
1st Stage
Heat
Pump “L”
Terminal
Connection
Cool
Mode
2nd Stage
No
Output
Heat
Mode
2nd Stage
No
Output
Multi-
Stage
Heat
Pump
HP2

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2. After installation, configure the thermostat to the
appropriate system type. Press “Menu” on the thermostat
and refer to these menu options as needed:
CONFIGURATION MENU ITEMS REFERENCE
No. Menu item Default Options
1Screen Brightness Off Adjust resting state brightness
with an option to turn off
2Nightlight Off Off / On
3Home Screen Content On
On
°F
Indoor Humidity
Time of Day
°F / °C
4Schedule - 5 / 2 Day Schedule
5Wi-Fi O Connect to Wi-Fi
6 Time Setup - Set the date and time
7About Thermostat Model Number / Reset
8Setup HVAC AC2 / EL2
AC2
EL2
O
Outdoor Setup AC1/
AC2/HP1/HP2/AC0
Indoor Setup GA1/
GA2/EL1/EL2/Fan
Reversing Valve Position O/B/3

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3. Once the thermostat is installed and properly configured,
test the equipment by following these steps:
• Turn on power to the system.
• Fan Operation
•If your system does not have a “G” terminal
connection, skip to “Heating System” below.
•Press the “Fan” button on the thermostat and select the
“On” position. The blower should begin to operate.
•Press the “Mode” button to turn off the system. Then
press the “Fan” button on the thermostat and select the
“Auto” position. The blower should stop immediately.

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• Heating System
•Press the “Mode” button on the thermostat
and select the “Heat” position.
•Press the up arrow on the thermostat and adjust the
setting to 1° above the current room temperature. The
heating system should begin to operate and the thermostat
display will turn red indicating heating on the screen.
•For heat pumps with auxiliary, press the up arrow
on the thermostat and adjust the setting to 3°
above the current room temperature. The auxiliary
heat should begin to operate and the thermostat
will indicate “Heating Auxiliary” on the screen.
•Press the down arrow on the thermostat and adjust
the setting to 1° below the current room temperature.
The heating system should stop operating and the
display will go back to a neutral gray color.

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• Auxiliary System (only for heat pumps with auxiliary)
•Press the “Mode” button on the thermostat and
select the “Aux” position. This bypasses the
heat pump and runs auxiliary-only heat.
•Press the up arrow on the thermostat and adjust the
setting to 1° above the current room temperature. The
auxiliary heating system should begin to operate and the
thermostat will indicate “Heating Auxiliary” on the screen.
•Press the down arrow on the thermostat and adjust
the setting to 1° below the current room temperature.
The auxiliary heating system should stop operating and
“Heating Auxiliary” will disappear from the screen.

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• Cooling System
•Press the “Mode” button on the thermostat
and select the “Cool” position.
•Press the down arrow and adjust the setting to 1° below
the current room temperature. The blower should come
on immediately on high speed, followed by cold air
circulation. The thermostat display will turn blue. Note
that there can be up to a 5 minute delay for this process.
This is indicated by a flashing setpoint temperature.
•Press the up arrow and adjust the setting to 1° above the
current room temperature. The cooling system should stop
operating and the display will go to a neutral gray color.
•If you encounter any issues while testing the equipment,
refer to the troubleshooting actions on page 14.

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SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
No Heat/
No Cool/
No Fan
(common
problem)
1. Blown fuse or
tripped circuit
breaker
2. Furnace power
switch to OFF
3. Furnace blower
compartment
door panel loose
4. Loose connection
to thermostat
or system
1. Replace fuse or reset breaker
2. Turn switch to ON
3. Replace door panel in proper
position to engage safety
interlock or door switch
4. Tighten connections
No Heat 1. Thermostat not
set to Heat
2. Loose connection
to thermostat
or system
3. Heating system
requires service
or thermostat
requires
replacement
1. Set thermostat to Heat.
2. Verify thermostat and system
wires are securely attached.
3. Diagnostic: Set Mode to Heat and
raise the setpoint above room
temperature. Within five minutes
the thermostat should make a soft
click sound and the display should
turn red. This sound indicates the
thermostat is operating properly.
If the thermostat does not click,
try resetting the thermostat. If
the thermostat does not click
after being reset, contact your
heating and cooling service
person or place of purchase for
a replacement. If the thermostat
clicks, verify the heating system
is operating correctly.
Troubleshooting

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SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
No Cool 1. Thermostat not
set to Cool
2. Loose connection
to thermostat
or system
3. Cooling system
requires service
or thermostat
requires
replacement
1. Set thermostat to Cool.
2. Verify thermostat and system
wires are securely attached.
3. Diagnostic: Set Mode to Cool
and lower setpoint below room
temperature. Same procedures as
diagnostic for “No Heat” condition
except set the thermostat to Cool
and lower the setpoint below the
room temperature. There may be
up to a five minute delay before
the thermostat clicks in Cooling if
the AC Protection feature is on.
Heat, Cool
or Fan Runs
Constantly
Possible short in
wiring, thermostat,
heat, cool or
fan system
Check each wire connection
to verify they are not shorted
or touching other wires. Try
resetting the thermostat.
Thermostat
Display &
Thermometer
Disagree
Thermostat display
requires adjustment Display can be adjusted +/-5° using the Temperature Offset in Sensi app.
Display is
Blank The display could be turned off of you
need a common
wire (c- wire)
Attach a common wire (c-wire)
or turn on the display.

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SYMPTOM POSSIBLE CAUSE CORRECTIVE ACTION
Furnace (Air
Conditioner)
Cycles Too
Fast or Slow
The location of the
thermostat and/
or the size of the
Heating System
may be influencing
the cycle rate
Digital thermostats provide precise
control and cycle faster than older
mechanical models. The system turns
on and off more frequently, but runs
for a shorter time. If you would like
to increase cycle time, choose Slow
for the Cycle Rate in the Sensi app.
“Call for
Service”
appears on
the screen
1. Heating or Cooling
system is not
able to heat/
cool the space to
within 5 degrees
of the setpoint
within 2 hours
2. If “--” is displayed
for the Room
Temperature,
a replacement
thermostat
is needed
3. None of the
buttons operate
on the thermostat
1. See corrective action for “No Heat”
See corrective action for “No Cool”
2. Replace thermostat
3. Make sure keypad lockout is
not turned on. If it’s OFF, try
resetting the thermostat.
Reset: Turn the power to your
system off, wait 5 seconds
and turn it back on.

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Connecting Sensi to Wi-Fi
1. Ask the homeowner to download the free Sensi app onto the
their iOS or Android device.
2. Ask the homeowner to follow the prompts to create
an account.
3. Once the homeowner has logged in, ask to use their device to
connect the thermostat to the Wi-Fi.
4. Select “Connect Thermostat to Wi-
Fi” and follow the in-app prompts to
complete the connection steps.
5. Once the thermostat is connected
to Wi-Fi, enter your registered phone
number by selecting “Contractor” from
the drop down menu.
QUICK TIP: You must have your customer’s Wi-Fi Network
(SSID) and Password, along with the Sensi Security Code
card to complete the wireless setup.

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Warnings
INSTALLER INFORMATION
FAILURE TO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE INSTALLING
OR OPERATING THIS CONTROL COULD CAUSE PERSONAL INJURY AND/OR PROPERTY
DAMAGE.
WARNING: OUT OF PHASE
TRANSFORMERS
On two transformer systems, the
transformers MUST be in phase.
Measure the voltage across RC
and RH. If more than 12 Volts AC is
present between RC and RH, then
the transformers are NOT in phase.
To correct this condition, reverse the
secondary low voltage connections
at either the Heating or Cooling
transformer.
To prevent electrical shock and/
or equipment damage, disconnect
electric power to system at
main circuit breaker box until
installation is complete.
FOR CALIFORNIA RESIDENTS:
WARNING:
This product contains a chemical
known to the state of California to
cause cancer and birth defects and
other reproductive harm.
VOLTAGE REQUIREMENTS
Do not use on circuits exceeding
specified voltage. Higher voltage will
damage control and could cause
shock or fire hazard.
Thermostat installation and all
components of the control system shall
conform to Class II circuits per the NEC
code.
CAUTION: E5 Alert
If “Call For Service” is displayed on
your Sensi thermostat, and E4 or E5
appears where the room temperature
should be displayed or the backlight
is flashing, please call our support
team immediately at 888.605.7131
ATTENTION: MERCURY NOTICE
This product does not contain mercury.
However, this product may replace
a product that contains mercury.
Mercury and products containing
mercury must not be discarded in
household trash. Refer to thermostat-
recycle.org for location to send
product containing mercury.

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For Your Customer
MAKE SURE TO LEAVE THE SENSI WELCOME GUIDE FOR
YOUR CUSTOMER.
It provides helpful instructions and information on the following:
•Includes their Sensi Security Code for connecting to Wi-Fi
•How to connect their Sensi thermostat to Wi-Fi (if this has
not already been completed) or connect additional devices
•Key features of the thermostat and the app and how they work
•Customer Support

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377682001