Penn A421 Series User manual

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).
Part No. 24-7664-3035 Rev D
2018-11-13 A421ABD-x, A421AED-x

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: use the
three-button touchpad on the Advanced Menu or connect a momentary switch to the binary input
(BI).
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide2

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 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.
3A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

• 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.
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.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide4

Wiring
Observe the following guidelines.
WARNING
Risk of Electric Shock
Disconnect or isolate all power supplies before making electrical connections. More than one
disconnection or isolation may be required to completely de-energize 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
isolations et débranchements sont peut-être nécessaires pour -couper entièrement l'alimentation de
l'équipement. Tout contact avec des composants porteurs 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 in accordance with local, national,
and regional regulations.
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: Electrostatic discharge (ESD) can damage A421 Controls. Use proper electrostatic
discharge precautions during installation and servicing to avoid damaging A421 Controls.
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.
5A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

• 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)
22 AWG 125 ft (38 m)
1 The maximum sensor cable lengths have less than 1°F (0.6°C) 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.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide6

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.
TB2
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.
28 AWG to
12 AWG
0.08 mm² to
4.0 mm²
7A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

Table 2: A421 Control wiring terminals and wire size information
Terminal
block
Label Description, function, and requirements Wire sizes
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.
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
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
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide8

• 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.
9A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

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.
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.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide10

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.
11A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

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
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
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide12

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
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. You
can perform the following actions in any parameter code screen:
The parameter code flashes on and off.
• To navigate through all of the parameter code screens, press Down or Up.
• To exit either menu and return to the Main screen, press Down and Up simultaneously.
You can perform the following actions in any parameter code screen:
The parameter value flashes on and off.
• To scroll through all of the available parameter values for the associated parameter code, press
Down or Up.
• 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.
13A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

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
To access the Basic menu and view and change the Basic parameter values, complete the following
steps:
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.
To exit the Basic menu and go to the Advanced menu, simultaneously press and hold Down and
Up, for 5 seconds.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide14

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.
15A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

Figure 8: Navigating the Advanced menu
Viewing and changing values in the Advanced menu
To access the Advanced menu and view and change the parameter values, complete the following
steps:
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
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide16

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 controller enforces the following behavior:
• 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 controller enforces the following behavior:
• 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)
To 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.
17A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

- 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
Control behavior when starting or stopping an automatically
enabled Defrost Off-Cycle
The controller enforces the following behavior:
• 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:
- 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)
1. To start or stop a Defrost Cycle using the Binary Input (BIN):
- 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 Figure 11.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide18

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 controller enforces the
following behavior:
• 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.
19A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

Figure 12: Adjustment behavior in Restricted Adjustment mode
Setting the control to Restricted Adjustment mode
To set up the restricted adjustment feature, complete the following steps:
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.
Figure 13: Repositioning the jumper to restrict control adjustment
Control adjustment is now restricted to changing only the OFF value, which shifts the On and OFF
control band within the restricted adjustment range defined by HtS and LtS (Figure 12).
Note: To completely restrict and lockout all user adjustment on the control, set the HtS value
equal to the On or OFF value and the LtS value equal to the OFF or On value. Then the (On to
OFF) control band is equal to the restricted adjustment range, LtS to HtS, and the OFF value
cannot be adjusted in the restricted mode.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide20