The purpose of this parameter is to prevent over-
cooling that could occur if a long Ont is used when
the outside air is very cold.
Note:
If LtS is left at the default value (40°F), the Ltt
parameter has little or no impact.
Minimum Relay On-Time (Ont)
Select the minimum relay On-time per cycle period
(cP). Ont is used when the sensed temperature
is greater that the LtS. The range of values are 0
seconds to 300 seconds.
During any relay On-time (Ont or Ltt), Ont is
displayed followed by the remaining Ont seconds
and the sensed temperature in sequence. This
sequence of three screens continues until the Ont
seconds expire for the cP.
When the fan relay is On for a temperature (free-
cooling) ventilation cycle, the screen displays the
sensed temperature and a snowflake in the lower-
right corner of the screen to indicate the fan relay
is On for free-cooling.
Cycle Period (cP)
Select the Cycle Period for free-cooling and
ventilation control. The range of values are zero 0
minutes to 60 minutes.
Sensor Offset Adjustment (So)
Sensor offset allows you to compensate for any
difference between the displayed temperature
value and the temperature sensed at the A99
sensor. Select a temperature value to offset the
temperature displayed on the LCD from the
temperature sensed at the sensor. The sensor
offset adjustment range is from -5°F to 5°F or -3°C
to 3°C in 1° increments.
Sensor Failure mode (SF)
Select whether the control’s fan relay operates as
energized or de-energized in the event of a sensor
or sensor wiring failure. When the control detects
a sensor circuit failure, the fan relay operates in
the selected sensor failure mode. The LCD flashes
SF
and
OP
if the sensor circuit is open or
SF
and
SH
if the sensor circuit is shorted.
Backlight Brightness Level (bll)
The backlight brightness level feature allows
you to adjust the LCD backlight intensity. At level
0 the backlight is off. Level 10 is the brightest
backlight setting and the system default. The
selected backlight brightness level is applied
to the LCD during normal operation. When you
enter the programming menus to set up the
control or press any key, the LCD automatically
goes to the brightest level. If you do not press a
key for 30 seconds, the main screen is displayed
and the backlight setting returns to the selected
brightness level.
Switch-Activated Override (Ord)
When a switch is closed between BIN and COM
terminals of the TB3, the control is overridden, and
the fan relay remains on. The fan relay remains On
until the circuit (toggle switch) between BIN and
COM is open.
The relay remains energized regardless of the
sensor value, sensor fail state, or any timing
parameters (cP, Ont, Ltt). The control display
alternates between the main display and manual
override (Ord).
Table 3: Standard parameter setup codes, descriptions,
range of values, and default values
Parameter
code
Parameter
description (menu)
Range of
usable
values
1
Factory
default
value
Un
Temperature Units
(Advanced only)
ºF or ºC
ºF
LtS
Low Temperature Stop
(Advanced only)
-40ºF to
212ºF
(-40ºC to
100ºC)
40ºF
HtS
High Temperature Stop
(Advanced only)
-40ºF to
212ºF
(-40ºC to
100ºC)
212ºF
OFF
Relay Off Temperature
(Basic, Advanced, and
Restricted)
-40ºF to
212ºF
(-40ºC to
100ºC)
70ºF
On
Relay On Temperature
(Basic and Advanced)
-40ºF to
212ºF
(-40ºC to
100ºC)
75ºF
Ltt
Low Temperature On-
Time (Advanced only)
0 seconds to
300 seconds
60 seconds
Ont
Minimum Relay On-
Time (Advanced only)
0 seconds to
300 seconds
60 seconds
cP
Cycle Period
0 minutes to
60 minutes
10 minutes
So
Sensor Offset
Adjustment (Advanced)
-5ºF to 5ºF
(-3 to 3ºC)
0ºF
SF
Sensor Failure Action
(Basic and Advanced)
0 = output
relay de-
energized
1 = output
relay
energized
1 output
relay
energized
bll
LCD Backlight
Brightness Level
Adjustment (Advanced
only)
0 to 10; 0 =
backlight
off, 10 =
brightest
backlight
setting
10 (brightest
backlight)
1
The default values for general application models are shown.
OEM models may have different default values.
A421 Series Electronic Temperature Controls with Cycle Timer Installation Guide
6
