Setup and adjustments
The front panel of the A421 Series Electronic Temperature
Control has an LCD and a three-button UI as shown in the
following figure.
Figure 5: A421 Control front panel with LCD and three-
button UI
LCD
The A421 Series Control has a backlit LCD screen (Figure
5). You can adjust the LCD brightness. During normal
operation, the LCD displays the Main screen, which
provides following information:
• Temperature sensed at the A99 sensor
• Selected temperature units (°F or °C)
• Mode of operation (snowflake = cooling mode only)
• Binary Input status (BIN) when a user-supplied toggle
switch is connected and closed to manually override the
relay control.
During setup and adjustment, the LCD displays the
parameter code screens and the parameter value screens.
See the
A421 Control parameter setup menus
information.
Three-button touchpad
The touchpad has three buttons for setup and adjustment
of the A421 Control (Figure 5). See
for more information on using the
three-button touchpad.
Relay status LED
The green LED on the front panel illuminates when the
SPDT output relay is energized and the LC and LNO
contacts are closed. See Figure 5.
Parameter codes and modes of
operation
Relay Off temperature (OFF)
Select the temperature at which the output relay
de-energizes, the LC to LNO relay contacts open
(cutout), and the green LED goes off. The range
of usable temperature values is -40°F to 212°F or
-40°C to 100°C in 1° increments.
Relay On temperature (On)
Select the temperature at which the output relay
energizes, the LC to LNO relay contacts close (cut
in), and the green LED lights. The range of usable
temperature values is -40°F to 212°F or -40°C to
100°C in 1° increments.
The A421 Series Control with Cycle Timer functions
in Cooling Mode only.
Temperature Units (Un)
Select the preferred temperature scale for your
application. Select either the Fahrenheit (°F) or
Celsius (°C) temperature scale.
Note:
After changing the value for the temperature
units (Un), confirm that the temperature values for
the other parameter codes are still correct for your
application.
Low Temperature Stop (LtS)
Select the lowest temperature value below
which the Low Temperature On-Time (Ltt) is
enforced. This parameter is also used when
control adjustment is restricted. See
.
The range of usable temperature values is -40°F to
212°F or -40°C to 100°C in 1° increments.
High Temperature Stop (HtS)
Select the highest temperature value in which the
On/OFF control band can be adjusted when the
control adjustment is restricted. See
.
The range of usable temperature values is -40°F to
212°F or -40°C to 100°C in 1° increments.
Restricted Adjustment mode
The HtS and LtS values define the restricted
adjustment temperature range and are enforced
only when the A421 Control is set to the restricted
adjustment mode (Figure 9). See
Low Temperature On-Time (Ltt)
Select the minimum relay On-time whenever the
sensed temperature is less than the LtS. The range
of values are 0 seconds to 300 seconds.
A421 Series Electronic Temperature Controls with Cycle Timer Installation Guide
5
