Penn A421 Series Manuale utente
A421 Series Electronic Temperature Controls
with Off-Cycle Defrost Installation Guide
Applications
Important: Use this A421 Series Electronic
Temperature Control only as an operating control.
Where failure or malfunction of the A421 Control
could lead to personal injury or property damage
to the controlled equipment or other property,
additional precautions must be designed into the
control system. Incorporate and maintain other
devices, such as supervisory or alarm systems or
safety or limit controls, intended to warn of or
protect against failure or malfunction of the A421
Control.
Important: Utiliser ce A421 Series Electronic
Temperature Control uniquement en tant que
dispositif de régulation. Lorsqu'une défaillance
ou un dysfonctionnement du A421 Control risque
de provoquer des blessures ou d'endommager
l'équipement contrôlé ou un autre équipement, la
conception du système de contrôle doit intégrer des
dispositifs de protection supplémentaires. Veiller
dans ce cas à intégrer de façon permanente d'autres
dispositifs, tels que des systèmes de supervision
ou d'alarme, ou des dispositifs de sécurité ou de
limitation, ayant une fonction d'avertissement
ou de protection en cas de défaillance ou de
dysfonctionnement du A421 Control.
The A421 Series Electronic Temperature Controls are
single-stage, electronic temperature controls with a single-
pole, double-throw (SPDT) output relay.
A421 Controls feature a backlit LCD with adjustable
brightness and three-button touchpad interface that you
can set up to restrict user adjustments. An LED indicates
the output relay's on/off status.
A421 Controls have simple on and off temperature
settings for heating or cooling, an adjustable anti-short
cycle delay, temperature setback, and sensor offset
capability. The temperature control range is -40°F to 212°F
or -40°C to 100°C.
The A421 Controls are available either in Type 1 (NEMA),
IP20 (CE), high-impact plastic enclosures suitable for
surface or DIN rail mounting (Figure 1), or in Type 4X
(NEMA), IP66 (CE) watertight, corrosion resistant surface
mount enclosures (Figure 2).
Dimensions
Figure 1: A421 Control with Type 1 (NEMA), IP20
enclosure dimensions, in. (mm)
Figure 2: A421 Control with Type 4X (NEMA), IP66
enclosure dimensions, in. (mm)
Off-Cycle Defrost control
You can use the A421 Control with Off-Cycle Defrost to
set up regular, passive defrost periods of 1 minutes to 99
minutes. The defrost interval can range from 2 hours to 24
hours, or you can set it to 0 for no defrost interval. You can
also start or stop a defrost cycle in the following two ways:
Part No. 24-7664-3035 Rev. D
2018-11-13
A421ABD, A421AED
use the three-button touchpad on the Advanced Menu or
connect a momentary switch to the binary input (BI).
The A421 with Defrost Control is typically used to provide
temperature control and adjustable, timed, passive defrost
cycles on medium temperature cooling applications such
as reach-in boxes, display cases, and walk-in coolers.
Parts included
Each A421 Control includes a Johnson Controls® or
PENN® A99 Series temperature sensor. See A99 Series
Temperature Sensors, Wiring, and Technical specifications
for more information about A99 sensors.
A99 Series Temperature Sensors
The A421 Controls require an A99 sensor, and each A421
Control includes an A99 sensor. Any A99 Series sensor
works with the A421 Series Controls. Do not replace an
A99 Series sensor with any other brand, series, or type
of temperature sensor. See Ordering information for
available A99 Series sensor models.
You can extend the sensor leads in the field. See Table 1
for wire sizes and lengths. On long sensor cable runs, use
shielded cable to reduce electromagnetic interference
(EMI). Observe EMI best practices when you route sensor
leads.
Do not completely immerse the A99 Series sensors in
water or any other liquid. The A99 sensors are moisture
tolerant and splash resistant but if you immerse the
sensor, liquid can enter the sensor probe where the steel
tube meets the wire cable and result in sensor failure,
which voids any warranty.
In applications where the sensor may be exposed to a lot
of moisture, splashing, or rain, it is best practice to mount
the sensor in a vertical position with the cable at the
bottom routed downward so that moisture can drain away
from the steel probe. Use a suitable bulb well for complete
fluid immersion applications. See Ordering information for
information about bulb wells.
The A99 Series sensors are positive temperature
coefficient (PTC) sensors. To test an A99 sensor,
disconnect the sensor from the control and measure
the resistance between the sensor leads in the following
situations:
• When the temperature at the sensor is 77°F (25°C), the
resistance should be 1,035 ohms.
• When the temperature at the sensor is 32°F (0°C), the
resistance should be 855 ohms.
See Troubleshooting for more information.
When you connect an A99 sensor to a standard A421
Control, the control restricts the range of usable values
from -40°F to 212°F (-40°C to 100°C).
See Wiring, Technical specifications, and refer to the
A99B Series Temperature Sensors Product/Technical Bulletin
(LIT-125186) for more information about A99 Series
sensors.
Mounting
Observe the following guidelines when you locate and
mount an A421 Control:
• Make sure that the mounting surface can support the
control, DIN rail, mounting hardware, and any user-
supplied panel or enclosure.
• Mount the control in a vertical, upright orientation
wherever possible. It is best practice to use DIN rail
mounting for type 1 controls.
• In direct-mount applications, mount the control on a
flat and even surface.
• Mount the control in a location free of corrosive vapors
and observe the ambient operating conditions listed
in Technical specifications for the A421 Control and the
A99 sensor.
• Allow sufficient space to connect and route wires, view
the LCD, and use the touchpad.
• Do not mount the control on surfaces that are prone
to vibration or in a location where high-voltage relays,
motor starters, other sources of electromagnetic
emissions, or strong radio frequency may cause
interference.
• Do not install the control in an airtight enclosure.
• Do not install heat generating devices with the
control in an enclosure that may cause the ambient
temperature to exceed 150°F (66°C).
Mounting a Type 1/IP20 control on DIN rail
1. Provide a section of 35 mm DIN rail that is longer
than the control width. Mount the DIN rail in a
suitable location and use appropriate mounting
hardware.
2. Clip the control module on the rail, position the
module’s upper DIN rail clips on the top rail, and
gently snap the lower clips on to the bottom of the
rail.
Direct-mounting a Type 1/IP20 control to
a wall or other flat surface using the four
keyhole slots
1. Disconnect the power and remove the enclosure
cover. Place the control horizontally against the wall
surface in a suitable location, and mark the keyhole
slot locations on the mounting surface.
2. Install appropriate screws or fasteners and leave the
screw heads approximately one or two turns away
from flush to the mounting surface.
3. Position the control mounting slots over the screw
heads, and then tighten the mounting screws to
secure the control to the surface.
Note: When you mount the control on an
uneven surface, use shims to mount the control
evenly.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide2
Additional guidelines for mounting Type
4X/IP66 controls
You can mount the Type 4X models to flat vertical surfaces
using the four holes at the enclosure corners. Place the
control against a flat wall surface in a suitable location,
and mark the mounting screw hole locations on the
mounting surface. Use appropriate screws and shims to
mount the control evenly on the surface.
On Type 4X models, select the knockout for removal. Place
a screwdriver blade on the knockout near the edge. Apply
a sharp blow to the screwdriver handle to loosen the
knockout. Be careful not to damage the control’s interior
components.
The A421 Control's temperature setback (BI) function
requires an additional low-voltage, two-wire cable for
operation. On Type 4X/IP66 enclosures, you must install a
suitable watertight fitting in an available knockout to pass
the two-wire cable through the enclosure wall.
You can rotate the control enclosure base on the Type 4X/
IP66 models 180º relative to the control enclosure cover
and LCD, to bring the electrical connection to the top or
bottom of the mounted control.
Note: Do not twist the wiring harness between the
enclosure base and cover more than 180º.
Wiring
Observe the following guidelines.
WARNING
Risk of Electric Shock
Disconnect or isolate all power supplies before mak-
ing electrical connections. More than one disconnec-
tion or isolation may be required to completely de-en-
ergize equipment. Contact with components carrying
hazardous voltage can cause electric shock and may
result in severe personal injury or death.
AVERTISSEMENT
Risque de Décharge Électrique
Débrancher ou isoler toute alimentation avant de
réaliser un raccordement électrique. Plusieurs iso-
lations et débranchements sont peut-être néces-
saires pour -couper entièrement l'alimentation de
l'équipement. Tout contact avec des composants por-
teurs de tensions dangereuses risque d'entraîner une
décharge électrique et de provoquer des blessures
graves, voire mortelles.
Important: Use copper conductors only. Make all
wiring connections in accordance with local, national,
and regional regulations. Do not exceed the A421
Control's electrical ratings.
Important: Do not exceed the A421 Control’s
electrical ratings. Exceeding the electrical ratings can
result in permanent damage to the control and void
any warranty.
Important: Run all low-voltage wiring and cables
separate from all high-voltage wiring. It is best
practice to use shielded cable input (sensor) cables
that are exposed to high electromagnetic or radio
frequency noise.
Important: Make all wiring connections in
accordance with the National Electrical Code and
local regulations. Use proper Electrostatic Discharge
(ESD) precautions during installation and servicing
to avoid damaging the electronic circuits of the A421
Control.
Important: Do not connect supply power to the
A421 Controls before checking all wire connections.
Short circuits or improperly connected wires can
result in damage to the modules and void any
warranty.
Important: When you connect an A99 sensor with a
shielded cable to an A421 Control, connect the cable
shield drain lead to the common (COM) terminal on
the sensor and binary input terminal block (TB3).
Do not connect the shield at any other point along
the cable, and isolate and insulate the shield along
the entire length of the sensor cable. If you connect
a cable shield at more than one point, transient
currents can flow through the sensor cable shield
and cause erratic control operation.
Observe the wire size restrictions listed in Table 2 and the
electrical ratings listed in Technical specifications.
Observe the following guidelines, procedures, and
illustrations when you wire an A421 Series control and A99
Series sensor.
• Select the appropriate A99 sensors for the ambient
operating range that the A421 Control monitors
and controls, as shown in Table 6. See Technical
specifications for more information.
• Keep the sensor leads as short as possible in your
application. The additional resistance in long
sensor cables creates an offset between the actual
temperature and the displayed temperature. See Table
1 when you extend sensor leads.
• A99 sensors are not polarity specific. You can connect
either lead to the SEN or COM terminals.
• It is best practice to use 22 AWG, stranded, twisted-pair
cable with a shield to extend sensor cable runs.
Table 1: Maximum sensor cable lengths and wire sizes
Wire
gauge
1Maximum sensor cable length1
16 AWG 500 ft (152 m)
18 AWG 300 ft (91 m)
20 AWG 200 ft (61 m)
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide 3
Table 1: Maximum sensor cable lengths and wire sizes
Wire
gauge
1Maximum sensor cable length1
22 AWG 125 ft (38 m)
1 At the listed maximum cable lengths, there is less than 1Fº
(0.6Cº) error between the temperature sensed at the A99
sensor and the temperature displayed on the LCD.
TB2 Terminal Block and SPDT relay output
The terminals LC, LNO, and LNC on the TB2 terminal block
connect to an SPDT dry-contact relay in the A421 Control
(Figure 3). The control does not provide any internal
power to the TB2 terminals or relay contacts. The A421
Control energizes and de-energizes the relay to open
and close the contacts based on the On/Off temperature
values.
• Relay De-energized (Off) = LC open to LNO as shown in
Figure 3, and the relay status LED is off
• Relay Energized (On) = LC closed to LNO and the relay
status LED is on
Figure 4 shows how to wire the A421 Control to use the
same power source that powers the controlled equipment
to also power the A421 Control.
Figure 3: TB2 Terminal Block showing connections to
the internal SPDT relay
You can also provide an independent power source for the
A421 Control on the TB1 terminals and then wire the TB2
relay terminals to a separate power source to switch and
power the controlled equipment circuit.
Figure 4: Wiring the A421 Series Controls using the
same power source to power the control operation and
power the controlled equipment
Table 2: A421 Control wiring terminals and wire size
information
Terminal
block
Label Description, function, and
requirements
Wire sizes
LN Line-voltage power source
(common): Connect the neutral
wire for 120 VAC supply power
applications. Connect the L1
supply power lead for all 208/240
VAC supply power applications.
120 V Line-voltage 120 VAC control
power (hot): Connect the 120 VAC
supply power (hot) for 120 VAC
supply power applications (via
jumper from LC in Figure 4).
TB1
120/240
VAC
Models
240 V Line-voltage 240 VAC control
power (L2) terminal: Connect
the L2 supply power connection
for 208/240 VAC supply power
applications through the jumper
from LC. (Figure 4).
28 AWG to
12 AWG
0.08 mm²
to
4.0 mm²
LC Line-voltage SPDT relay common
contact: Connect power supply
to power the controlled load.
Connect 120 VAC (hot) for 120
VAC applications and L2 for
208/240 VAC applications.
LNO Line-voltage SPDT relay normally
open contact: Connects
controlled equipment to the line-
voltage normally open (LNO)
contact on the SPDT relay. When
LC is closed to LNO, the relay
is energized and the green
LED is on. The LNO terminal
typically provides power to the
controlled equipment in cooling
and heating applications.
TB2
LNC Line-voltage SPDT relay normally
closed contact: Connects
controlled equipment to the line-
voltage normally closed (LNC)
contact on the SPDT relay. When
LC is closed to LNC, the relay is
de-energized and the green LED
is off. The LNC terminal is not
typically wired to the controlled
equipment.
28 AWG to
12 AWG
0.08 mm²
to
4.0 mm²
BIN Detects a switch closure between
the BIN and COM terminals and
manually starts or stops a defrost
cycle. This is now the default
behavior for the binary input.
COM Connects the low-voltage
common from the sensor and
binary input.
TB3
SEN Connects the low-voltage input
signal wire from control sensors.
22 AWG
(0.34 mm²)
stranded,
shielded
cable
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide4
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 the following information:
• Temperature sensed at the A99 sensor
• Selected temperature units (°F or °C)
• Mode of operation (Flame = Heating mode, Snowflake =
Cooling mode)
• Binary Input status (BIN) when a user-supplied
momentary switch is connected and closed to manually
start or stop a defrost cycle.
During setup and adjustment, the LCD displays the
parameter code screens and the parameter value screens.
See the A421 Control parameter setup menus for more
information.
Three-button touchpad
The touchpad has three buttons for setup and adjustment
of the A421 Control (Figure 5). See Navigating the Basic
and Advanced menus for more information about 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 (-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 (-40°C to
100°C) in 1° increments.
Heating or Cooling mode of operation
When you select your required On and OFF values,
the control automatically determines the mode of
operation and displays the proper mode icon on
the Main screen.
Note: The A421 Series Controls do not have jumpers
for setting up the heating or cooling mode.
The heating or cooling mode is determined by the
On and OFF value relationship as follows:
•OFF > On = Heating mode = Flame icon
•OFF < On = Cooling mode = Snowflake icon
Important: During normal operation,
adjusting just the On value or just the OFF
value on the A421 Control changes the
differential between On and OFF, and can
potentially change the mode of operation
from heating to cooling or cooling to
heating. To maintain a constant differential
between on and off, you must adjust both
the On and OFF values by an equal number
of degrees, or set up the control in the
Restricted Adjustment mode. See Restricting
user adjustment.
Anti-Short Cycle Delay (ASd)
Select the minimum time that the output relay
remains off (de-energized) before the next on-
cycle can start. The ASd interval overrides any
load demand (On) and does not allow the output
relay to go on until the selected ASd interval has
elapsed. See the following figure.
Figure 6: Anti-short cycle delay (ASD)
Anti-short cycle delay is typically used for
refrigeration applications so that the system
pressure can equalize before restarting the
compressor.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide 5
Note: When the ASd value is greater than 0, the
delay interval initiates every time that the A421
Control powers on and every time that an off-
cycle begins. When the ASd interval is activated,
the temperature sensed at the A99 sensor and the
parameter code ASd flash alternately on the LCD.
You can set the ASd interval from 0 minutes to 12
minutes, in 1 minute increments.
Sensor Failure mode (SF)
Select whether the control’s output 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 output 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.
Temperature Units (Un)
Select the preferred temperature scale for your
application. Select either the Fahrenheit (°F) or
Celsius (°C) temperature scale.
Note: After you change the temperature units value
(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 that the On/
OFF control band can be adjusted to when control
adjustment is restricted.
High Temperature Stop (HtS)
Select the highest temperature value that the On/
OFF control band can be adjusted to when control
adjustment is restricted.
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 12). See Restricting user
adjustment.
Note: It is best practice to leave HtS and LtS at their
default values, unless you intend to use the restricted
adjustment mode.
Note: If you use the Temperature Setback feature
in the Restricted Adjustment mode, the effective On
and OFF setback values (On + tBs and OFF + tBs) can
be greater than the selected HtS value or less than
the selected LtS value.
Temperature Setback (tSb)
Select a temperature value for setting back
the On and OFF temperature values. When a
user-supplied switch between the BIN and COM
terminals closes, note the following changes:
• The Main screen displays BIN in the upper-right
corner of the LCD.
• The temperature setback feature is enabled
and the control uses the effective On and OFF
setback values (On + tSb and OFF + tSb) to
control the relay.
Note: The control displays only the original On and
OFF values in the normal and setback modes. The
effective setback On and OFF values (On + tSb and
OFF + tSb) never display on the control LCD.
The temperature setback adjustment range
is from -50°F to 50°F (-30°C to 30°C). Typically,
heating applications require a negative
temperature setback (tSb) value, and cooling
applications require a positive value.
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 (-3°C to
3°C) in 1° increments.
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 displays and the
backlight setting reverts to the selected brightness
level.
Defrost Cycle Time (dFt)
Select the time in minutes that the defrost cycle
overrides On and keeps the relay Off. The dFt
value can be between 1 minutes and 99 minutes.
When the defrost cycle is On, the control is NOT
running and the LCD displays the following
screens: dEF (defrost mode), minutes remaining,
and the temperature at the sensor. When the dFt
is complete, the control returns to normal (On/Off
cycle) operation.
Defrost Interval (dI)
Select the time in hours between the start of a
defrost cycle and the next defrost cycle. The dI
value can be set to 0 or 2 hours to 24 hours.
Note: At the initial power On, the defrost interval (dI)
does NOT have a defrost cycle (dFt). The subsequent
defrost intervals begin with the selected dFt.
Setting the dl value to 0 eliminates regular or
timed defrost cycles. You can still start or stop a
defrost cycle by setting the SdF parameter or by
using the binary input.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide6
Start or Stop Defrost Cycle (SdF)
The Start/Stop Defrost Cycle parameter allows
you to start a defrost cycle, when the control is in
normal (On/Off cycle) operation, or stop a defrost
cycle when the defrost cycle is On.
Change to the SdF value to 1 to start a defrost
cycle. Or, change the value to 0 to stop the
defrost cycle, and return to normal (On/Off cycle)
operation.
Binary Input modes (bIn)
The BIN mode allows you to select how the A421
Control operates when a user-supplied binary
switch connected across BIN and COM on the TB3
terminal block is used with the control.
Set the BIN parameter to 0 to use the temperature
setback feature. Set the value to 1 and connect a
user-supplied momentary contact switch to start
or stop a defrost cycle.
Table 3: Standard parameter setup codes, descriptions,
range of values, and default values
Parameter
code
Parameter description
(menu)
Range of
usable
values
Factory
default
value11
Un Temperature Units
(Advanced only)
ºF or ºC ºF
OFF Relay Off Temperature
(Basic, Advanced, and
Restricted)
-40ºF to
212ºF
(-40ºC to
100ºC)
25ºF
On Relay On Temperature
(Basic and Advanced)
-40ºF to
212ºF
(-40ºC to
100ºC)
30ºF
ASd Anti-Short Cycle Delay
(Basic and Advanced)
0 minutes to
12 minutes
1 minute
tSb Temperature Setback
(Advanced only)
-50ºF to 50ºF
(-30ºC to
30ºC)
0ºF
So Sensor Offset
Adjustment (Advanced
only)
-5ºF to 5ºF
(-3ºC to 3ºC)
0ºF
HtS High Temperature Stop
(Advanced only)
-40ºF to
212ºF
(-40ºC to
100ºC)
212ºF
LtS Low Temperature Stop
(Advanced only)
-40ºF to
212ºF
(-40ºC to
100ºC)
-40ºF
SF Sensor Failure Action
(Basic and Advanced)
0 = output
relay de-
energized
1 = output
relay
energized
1 output relay
energized
Table 3: Standard parameter setup codes, descriptions,
range of values, and default values
Parameter
code
Parameter description
(menu)
Range of
usable
values
Factory
default
value11
bLL LCD Backlight
Brightness Level
Adjustment (Advanced
only)
0 to 10; 0 =
backlight
off, 10 =
brightest
backlight
setting
10 (brightest
backlight)
dFt Defrost Cycle Time
(Advanced only)
1 minutes to
99 minutes
30 minutes
dI Defrost Interval
(Advanced only)
0 or 2 hours
to 24 hours
8 hours
SdF Start or Stop Defrost
Off-Cycle (Advanced
only)
Change 0 to
1 to Start a
new Defrost
Cycle
Change 1 to
0 to Stop a
Defrost Cycle
0
bIn Binary Input Mode
(Advanced only)
0 =
Temperature
Setback
Mode
1 = Start
Defrost Cycle
Mode
1
1 The default values for general application A421 models are
shown. OEM A421 models may have different default values.
A421 Control parameter setup menus
The A421 Temperature Controls have a Basic and an
Advanced setup menu. You can use these menus to
scroll through the parameter setup codes, view and
edit parameter values, and set up your control for your
application requirement. The control also has a Restricted
adjustment menu. See Restricting user adjustment for
more information.
Note: The A421 Control retains a copy of the saved
parameter values in memory. When you change
and save a new value, the new value immediately
overwrites the previous value and saves to memory.
In the event of a power failure, brown out, or when
you disconnect power from the control, all of the
current parameter values in memory are retained.
Reconnecting power to the control restores all of the
saved values.
Navigating the Basic and Advanced
menus
The A421 Control buttons and display operate the same
way in the Basic and Advanced menus. The parameter
code flashes on and off in any parameter code screen.
1. To navigate through all of the parameter code
screens, press Down or Up.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide 7
2. To exit either menu and return to the Main screen,
press Down and Up simultaneously.
3. While in any parameter value screen, the parameter
value flashes on and off.
4. To scroll through all of the available parameter values
for the associated parameter code, press Down or
Up.
5. With the preferred parameter value displayed,
press MENU to save the value and go to the next
parameter code screen.
Note: If you do not press MENU to save a new
value, the control reverts to the last saved
value. After 30 seconds of inactivity, while in any
screen, the control reverts to the Main screen.
Basic menu
Use the Basic menu to quickly edit the On and OFF
temperature values, as well as the Sensor Failure Mode
(SF) and the Anti-Short Cycle Delay (ASd) value.
See Parameter codes and modes of operation and Table
3 for more information about parameter codes, usable
parameter values, and default values.
Figure 7: Navigating the Basic menu
Viewing and changing values in the Basic
menu
In this task you access the Basic menu and view and
change the Basic parameter values.
1. On the Main screen, press MENU. The LCD displays
OFF, which is the first parameter code screen
displayed in the Basic menu.
2. To scroll through all of the basic parameter codes
and display the preferred code, press Down or Up
3. With the preferred parameter code displayed, press
MENU to display the current parameter value for the
code.
4. With the current parameter value displayed, press
Down or Up to scroll through all of the parameter’s
usable values and display the preferred value.
5. With the preferred parameter value displayed, press
MENU to save the displayed value and go to the next
parameter code.
6. To exit the Basic menu and go to the Advanced menu,
simultaneously press and hold Down and Up, for 5
seconds.
Advanced menu
You can use the Advanced menu to change the parameter
values in the Basic menu and the parameter values for the
following advanced parameter codes:
• Temperature Units (Un)
• Low Temperature Setpoint Stop (LtS)
• High Temperature Setpoint Stop (HtS)
• Anti-Short Cycle Delay (ASd)
• Defrost Cycle Time (dFt)
• Defrost Interval (dI)
• Binary Input Mode (bLn)
• Backlight Brightness Level (bLL)
• Temperature Setback (tSb)
• Sensor Offset (So)
• Sensor Failure Option (SO)
• Start or Stop Defrost Cycle (SdF)
See Parameter codes and modes of operation and Table
3 for more information about parameter codes, usable
parameter values, and default values.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide8
Figure 8: Navigating the Advanced menu
Viewing and changing values in the
Advanced menu
In this task you access the Advanced menu and view and
change the parameter values.
1. On the Main screen, press and hold Down and Up
simultaneously for 5 seconds. Un displays on the LCD,
which is the first parameter code screen displayed in
the Advanced menu.
2. To scroll through all of the advanced parameter
codes and display the preferred code, press Down or
Up.
3. With the preferred parameter code displayed, press
MENU to display the current parameter value for the
code.
4. With the current parameter value displayed, press
Down or Up to scroll through all of the parameter
code’s usable values and display the preferred value.
5. With the preferred parameter value displayed, press
MENU to save the displayed value and go to the next
parameter code.
Setting up a regular or timed Defrost
Off-Cycle
The following behavior is enforced:
• At power up, the initial Defrost Interval (dI) does not
have a Defrost Cycle (dFt).
• Subsequent defrost intervals (dI) begin with the
selected dFt value.
• All defrost intervals have the same length.
To set up a regular or timed defrost cycle:
1. Select a dI value between 2 hours and 24 hours.
Note: A dI value of 0 indicates no defrost
interval.
2. Select a dFt value between 1 minute and 99 minutes.
See Figure 9.
Figure 9: Typical passive Defrost Cycle behavior
Control behavior when manually starting or
stopping a Defrost Off-Cycle
The following behavior is enforced:
• Manually start a Defrost Cycle. The control returns to
normal On/Off operation after the defrost cycle time
(dFt) is complete.
• Manually stop a Defrost Cycle. The defrost cycle time
(dFt) is terminated and the control is returned to
normal On/Off operation.
Manually starting and stopping a Defrost Cycle
(SdF)
In this task you manually Start/Stop a Defrost Cycle (SdF).
1. Select a Defrost Interval (dI) value of 0.
2. Select a dFt value between 1 minute and 99 minutes.
3. Select an SdF parameter value of 1 during normal
On/Off operation to start a defrost cycle.
- Or, change the SdF value to 0 during a defrost cycle
and return to normal On/Off operation. See the
figure below.
Figure 10: Manual Defrost only: behavior when dI is set to 0
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide 9
Control behavior when starting or stopping
an automatically enabled Defrost Off-Cycle
The following behavior is enforced:
• At power up, the initial Defrost Interval (dI) does not
initiate a Defrost Cycle Time (dFt).
• A defrost cycle occurs at the beginning of each
subsequent defrost interval.
• You can start or stop a defrost cycle using the SdF
parameter or binary input (BIN).
• Starting a defrost cycle terminates the defrost interval
(dI) and starts a new defrost cycle.
• Stopping a defrost cycle terminates the dFt and
continues the current defrost interval (dI) until the start
of the next regular dI and defrost cycle.
Starting or stopping a Defrost Cycle using the
SdF parameter
1. To start or stop a Defrost Cycle using the SdF
parameter, choose from the following options.
- Select a Start/Stop Defrost Cycle (SdF) parameter
value of 1.
- Or, change the SdF value to 0 (zero) during a dFt
to stop a defrost cycle and return the control to
normal On/Off operation. See Figure 11.
Starting or stopping a Defrost Cycle using the
binary input (BIN)
In this task, you start or stop a Defrost Cycle using the
Binary Input (BIN).
1. Connect a momentary contact switch between BIN
and COM on the T3 terminal block.
Each time the momentary contact switch is pressed,
the defrost cycle starts or stops depending on
whether the defrost cycle is running or not. See Fig-
ure 11.
Figure 11: Starting and stopping a dFT: behavior using SdF
parameter and momentary contact switch
Restricting user adjustment
You can restrict user adjustment of the A421 Control to the
OFF value control band adjustment within a defined range
(Figure 12) or no user adjustment at all.
To set the A421 Control to the restricted adjustment
mode, position the P1 jumper located on the circuit board
next to the TB3 terminal block. See Setting the control to
Restricted Adjustment mode.
Note: Setting the A421 Control up in the Restricted
mode prevents casual users from over-adjusting the
control in your application, or from inadvertently
changing the mode of operation from cooling to
heating or heating to cooling (by over-adjusting the
On value or OFF value).
When the A421 Control is set up in the restricted
adjustment mode, the following behavior is enforced:
• The selected HtS and LtS values define the restricted
temperature adjustment range..
• The On and OFF values define the control band
differential, and the control band between On and OFF
remains fixed and not adjustable.
• Only the OFF value can be adjusted, the control band
remains fixed, and the On value automatically shifts
equal to the OFF value adjustment.
• The OFF value can only be adjusted to values that
maintain the entire control band within the restricted
temperature adjustment range defined by HtS and LtS.
See Figure 12.
• The basic and advanced menus are not available. Only
the Restricted Adjustment mode menu is available and
only the OFF value can be adjusted. See Figure 14.
Figure 12: Adjustment behavior in Restricted Adjustment
mode
Setting the control to Restricted
Adjustment mode
In this task you set up the restricted adjustment feature.
1. To make sure that the A421 is not in restricted mode,
position the jumper on both pins. See Figure 13.
2. Select the OFF and On values that define the
application’s required control band (Figure 12).
3. Change the HtS and LtS temperature values to define
the restricted adjustment range (Figure 12).
4. Disconnect power to the control and reposition the
jumper to one pin (Figure 13). Reconnect the power.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide10
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