The cooling fan delay setting will
delay the fan from coming on in
cool mode and keep it running
after the compressor shuts off
for a short time to save energy in
some systems.
Cooling Fan
Delay
OFF
You can set the cooling fan
delay to OFF, 15, 30, 60 or 90
seconds. If 15, 30, 60, or 90 is
selected the fan will not turn
on for that many seconds
when there is a call for cool
and will run for that many
seconds after satisfying a call
for cool.
COOL
FAN DL
IAQ Mode
Cycle
This feature will configure the fan
to run a selected number of cycles
per hour.
Note: This mode can be enabled
or disabled at anytime during
normal operation by selecting IAQ
mode with the fan key.
Select OFF, 1, 2, 3 or 4 with the
or keys.
This sets the number of cycles
per hour that the IAQ fan mode
will operate.
OFF
IAQ
MODE
CYCLE
Tech Setup Steps
Adjustment Options
Default
LCD Will Show
Technician Setup Menu
For Dual Fuel applications (Gas/
Fossil fuel Auxiliary Heat), turn
this setting ON to LOCKOUT the
Heat Pump (Y) when Auxiliary
Heat (W2) is on. If desired - This
can also be used with Electric
Auxiliary.
You can configure the system
switch for the particular
application.
Heat - Off - Cool, Heat - Off, Cool -
Off, Heat - Off - Cool - Auto
Note: EM. Heat will show if in
heat pump mode.
System Set
Use the or key until
the desired application is
flashing.
AUTO=
(Auto Changeover)
You can configure the thermostat
to operate a 3 stage heat pump
system.
2H 2C = 2 heat, 2 cool
3H 2C = 3 heat, 2 cool
This feature is shown only if the
HEAT PUMP technician setup
step is ON.
Stages of
Heat
Use the or key to
change between 2 or 3
stages of heat. 2 heat will
use Y1 as first stage and W2
as auxiliary.
3 heat will use Y1 as the first
stage, Y2 as the second stage
and W2 as the auxiliary.
Dual Fuel
Auxiliary for
Heat Pump
Will only appear if
Heat Pump setting is
turned ON
OFF
Will allow Y(1st stage of
Heat) and W2 (Aux Heat) to
run together if called for.
ON
Will de-energize Y termi-
nal 45 seconds after a call for
Auxiliary Heat (W2).
Heat Pump
When turned on the thermostat
will operate a heat pump.
1. EM. Heat will show as an option
in the system switch.
2. Y will be first stage of heat
& cool, W/E will be emergency
heat relay & W2 will be auxiliary
heat relay.
OFF configures the thermostat
for non heat pump systems.
ON configures the thermostat
for heat pump systems.
OFF
HEAT
OFF
COOL
A6
OFF
OFF
2H2C
2
STAGES
Tech Setup Steps
Adjustment Options
Default
LCD Will Show
Technician Setup Menu
This feature allows the installer
to change the calibration of the
room temperature display. For
example, if the thermostat reads
70˚ and you would like it to read
72˚ then 2.
OFF
This feature will flash a reminder
after the elapsed run time to
remind the user to change the
filter. A setting of “OFF” will
disable this feature.
Filter Change
Reminder
You can adjust the filter
change reminder from “OFF”
to 2000 hours of runtime in
50 hour increments.
Tech Setup Steps
Room
Temperature
Calibration
0˚F
This feature allows the installer
to select the minimum run
time for the compressor. For
example, a setting of 4 will force
the compressor to run for at
least 4 minutes every time the
compressor turns on, regardless
of the room temperature.
You can set the minimum
compressor run time to “OFF”,
“3”, “4”, or “5” minutes. If 3,4
or 5 is selected, the
compressor will run for
at least the selected time
before turning off.
Minimum
Compressor
On Time
OFF
You can adjust the room
temperature display to read
up to 4˚above or below the
factory calibrated reading.
Adjustment Options
Default
LCD Will Show
OFF
SE
CAL
0
O
F
OFF
Technician Setup Menu
This thermostat has a technician setup menu for easy installer
configuration. To set up the thermostat for your particular application:
1. Press the
MENU
button.
2. Press and hold the
TECH SETUP
button for 3 seconds. This 3
second delay is designed so that homeowners do not accidentally
access the installer settings.
3. Configure the installer options as desired using the table below.
Use the or keys to change settings and the
NEXT
STEP
or
PREV
STEP
key to move from one step to another.
Note:
Only press the
DONE
key when you want to exit the
Technician Setup options.
4. Press the
DONE
key to exit.
Keypad Lockout Note:
The selected keypad lockout functionality must
be activated after exiting tech setup. If you do not perform this
procedure, all keys will function freely. To lock the keypad hold down
the and keys for 3 seconds. You will see a lock in the display. To
unlock the display hold down the and keys for 3 seconds.
The compressor short cycle delay
protects the compressor from
“short cycling”. This feature will
not allow the compressor to be
turned on for 5 minutes after it
was last turned off.
Compressor
Short Cycle
Delay
ON
Selecting “ON” will not allow
the compressor to be turned
on for 5 minutes after the
last time the compressor was
on. Select “OF” to remove
this delay.
CO
ON
OF
Tech Setup Steps
Adjustment Options
Default
LCD Will Show
Keypad
Lockout
Keypad lockout allows you to
configure the thermostat so that
some or all of the keys don’t
function.
OF= keypad lockout has been
disabled.
PA= partial keypad lockout,
which locks all the keys except
the or keys.
FU= full keypad lockout,
which locks out all the keys.
OF
See Keypad Lockout Note
PA
The swing setting often called
“cycle rate”, “differential” or
“anticipation” is adjustable. A
smaller swing setting will cause
more frequent cycles and a larger
swing setting will cause fewer
cycles.
Cooling
Swing
The cooling swing setting
is adjustable from 0.2˚ to
2˚. For example: A swing
setting of 0.5˚ will turn the
cooling on at approximately
0.5˚ above the setpoint
and turn the cooling off at
approximately 0.5˚ below
the setpoint.
The swing setting often called
“cycle rate”, “differential”, or
“anticipation” is adjustable. A
smaller swing setting will cause
more frequent cycles and a larger
swing setting will cause fewer
cycles.
Heating
Swing
0.5
dFCO
0.5˚
The heating swing setting is
adjustable from 0.2˚ to 2˚.
For example: A swing setting
of 0.5˚ will turn the heating
on at approximately 0.5˚
below the setpoint and turn
the heating off at 0.5˚ above
the setpoint.
0.4˚
0.4
dFHE
Swing Setting Tip
The second stage will turn on at 2x the swing setting. The second stage
will turn off when 1x the swing is reached. For example, if the swing
setting is .5 degrees for heating and the thermostat is set at 70
˚
F, the first
stage will turn on at approximately 69.5
˚
F. The second stage will turn on
at 69
˚
F. The second stage will turn off at 69.5
˚
F and the first will turn off
at 70.5
˚
F. If the third stage is used, it will turn on at 68.5
˚
F and turn off at
approximately 69
˚
F.
Technician Setup Menu
HEAT
OFF
COOL
You can configure the thermostat
for one of three remote sensor
applications: 0 No Sensor, 1
Indoor, 2 Outdoor, 3 Floor.
Remote
Sensor
Operation
0
REMOTE
MODE
Local Temp
Sensor
You can disable the sensor on the
T855S thermostat. At least one
R251S indoor remote sensor must
be connected to disable the local
T855S sensor.
Note:
Will only
show if remote sensor is set to 1.
ON enables local T855S sensor.
OFF disables local T855S
sensor.
ON
LOCAL
TEMP
1
Use the or keys to
select one of three options.
View the S1/S2 terminal chart
on next page for an
explanation of these options.
ON
Number
of Indoor
Remotes
Enables the use of up to sixteen
indoor sensors R251S.
Note:
Will only show Remote
Sensor is set to 1 and Local Temp
Sensor is set to on.
You can use 1, 4, 9, or 16
indoor sensors. Refer to the
R251S Install Manual for
detailed connection
information.
ON
NUMBER
OF
REMO
1
A Note about IAQ Mode
This programmable/selectable mode will operate the fan 1-4 cycles per hour,
1-45 minutes per cycle. Once programmed in tech setup, to enable this mode
select “IAQ” with the fan key. Disable this mode by selecting “ON” or “AUTO” with
the fan key.
This allows you to select the
minimum number of minutes
that the fan will run per IAQ mode
cycle. The thermostat will keep
track of fan runtime from normal
heat and cool operation. If addi-
tional fan runtime is needed, the
thermostat will run the fan to
satisfy the IAQ mode minutes.
IAQ Mode
Minutes
Select 1, 5, 10, 15, 20, 30 or
45 minutes.
When IAQ fan mode is
enabled, it will ensure the
fan runs at least the selected
number of minutes per IAQ
Mode Cycle.
This step will not appear if
previous step is set to “OFF”.
1
IAQ
MODE
MINUT
COMP DELAY
COOL SWING
HEAT SWING
KEY LOCK
CALIBRATE
MAIN COMP
HEAT PUMP
SYSTEM SET
GAS AUX
OFF
OFF
1
