Penn A421 Series User manual

A421 Series Standard Electronic Temperature
Controls 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.
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)
Parts included
Each A421 Control includes a Johnson Controls® or
PENN® A99 Series temperature sensor. Refer to A99 Series
Temperature Sensors documentation for details.
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 information about 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.
Part No. 24-7664-3019 Rev. E
2019-10-14
A421ABC, A421AEC, A421GBF,
A421GEF

In applications where the sensor may be exposed to a
lot of moisture, splashing, or rain, mount the sensor in
a vertical position with the cable at the bottom routed
downward so that moisture can drain away from the
stainless 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 or -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 vertically 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 Standard Electronic Temperature Controls Installation Guide2

Wiring
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 for 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
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 7. 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 (150 m)
18 AWG 300 ft (100 m)
20 AWG 200 ft (60 m)
22 AWG 125 ft (40 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
A421 Series Standard Electronic Temperature Controls Installation Guide 3

Figure 3: TB2 Terminal Block showing connections to
the internal SPDT relay
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.
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 Low-voltage 24 VAC control power
(common): Connect the 24 VAC
supply power to operate the
control.
TB1
24 VAC
Models
24 V Low-voltage 24 VAC control power
(hot): Connect 24 VAC supply
power to operate the control (via
jumper from LC in Figure 4).
28 AWG to
12 AWG
0.08 mm² to
4.0 mm²
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 through the
jumper from LC. (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: Connects power supply
to power the controlled load.
Connect 24 VAC (hot) for 24 VAC
applications; 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
enables the selected temperature
setback (tSb) value.
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 Standard Electronic Temperature Controls Installation Guide4

Replacing an A419 Control with an A421
Control: Terminal locations and labels
The A421 Series Electronic Temperature Controls are the
next generation of the A419 Series Electronic Temperature
Controls.
If you need to replace an A419 Control with an A421
Control, be sure to note that wiring terminals on the TB1
and TB2 terminal blocks on A421 Controls are in different
positions and have different terminal labels from the
wiring terminals on the A419 Controls. Table 3 provides a
cross-reference for matching the terminal labels on A419
Controls to the terminal labels on A421 Controls.
Note: The low-voltage signal terminals on the TB3
terminal block are labeled the same on both A419
Controls and A421 Controls.
See Figure 4 for terminal block and terminal positions on
the A421 Control.
Table 3: A419 and A421 wiring terminal labels
Terminal block A419 Terminal label A421 Terminal label
T1 LNTB1
(24 VAC) T2 24V
120 120V
240 240V
TB1
(120/240 VAC)
AC COM LN
C LC
NO LNO
TB2
(All Voltages)
NC LNC
Setup and adjustments
The front panel of the A421 Series Electronic Temperature
Control has an LCD and a three-button UI (Figure 5).
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 binary
input (switch) is connected and closed to enable the
temperature setback feature.
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
A421 Series Standard Electronic Temperature Controls Installation Guide 5

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
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 is 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 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 9). 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 both 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
A421 Series Standard Electronic Temperature Controls Installation Guide6

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.
Table 4: Standard parameter setup codes, descriptions,
range of values, and default values
Parameter
code
Parameter
description
(menu)
Range of
usable values
1Factory
default
value1
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 4: Standard parameter setup codes, descriptions,
range of values, and default values
Parameter
code
Parameter
description
(menu)
Range of
usable values
1Factory
default
value1
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 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 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 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.
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.
A421 Series Standard Electronic Temperature Controls Installation Guide 7

See Parameter codes and modes of operation and Table
4 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 or 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)
• Temperature Setback (tSb)
• Sensor Offset (So)
• High Temperature Setpoint Stop (HtS)
• Low Temperature Setpoint Stop (LtS)
• Backlight Level (bLL)
See Parameter codes and modes of operation and Table
4 for more information about parameter codes, usable
parameter values, and default values.
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 Advanced parameter values.
1. On the Main screen, press and hold Down or 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.
A421 Series Standard Electronic Temperature Controls Installation Guide8

5. With the preferred parameter value displayed, press
MENU to save the displayed value and go to the next
parameter code.
Restricting user adjustment
You can restrict user adjustment of the A421 Control to
the OFF value control band only and limit the range of this
value (Figure 9).
To set the A421 Control the restricted adjustment mode,
position the 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 9.
• 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 11.
Figure 9: 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 10.
2. Select the OFF and On values that define the
application’s required control band (Figure 9).
3. Change the HtS and LtS temperature values to define
the restricted adjustment range (Figure 9).
4. Disconnect power to the control and reposition the
jumper to one pin (Figure 10). Reconnect power.
Figure 10: 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 9).
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.
Adjusting the control in Restricted mode
In this task you adjust the OFF value and shift the On and
OFF control band within the restricted adjustment range,
when the control is in the restricted adjustment mode.
1. On the Main screen, press MENU to go to the
Restricted Adjustment mode menu and display the
OFF parameter code screen (Figure 11).
2. To go to the OFF value screen, press MENU again.
3. On the OFF value screen, press Down or Up
to change the OFF value within the restricted
adjustment range.
4. To save the selected OFF value and return to the OFF
code screen, press MENU.
5. To return to the Main screen, press Down or Up
simultaneously.
A421 Series Standard Electronic Temperature Controls Installation Guide 9

Figure 11: Adjusting temperature in the Restricted menu
Troubleshooting
A421 Series Controls display fault codes on the LCD as
described in the following table.
Table 5: Fault codes
Fault code Definition System status Solution
SF flashes
alternately
with OP
Open
temperature
sensor or
sensor wiring
Output
functions
according to
the selected SF
mode
See Troubleshooting
procedure. Cycle
power to reset the
control.
SF flashes
alternately
with SH
Shorted
temperature
sensor or
sensor wiring
Output
functions
according to
the selected SF
mode
See Troubleshooting
procedure. Cycle
power to reset the
control.
EE Program
failure
Output is off To reset the control,
press MENU. If
problems persist,
replace the control.
Troubleshooting procedure
1. Check for proper voltage to the A421 Control.
a. To remove the cover, loosen the two captive cover
screws.
b. Use an AC voltmeter to check the voltage between
the COM and 120 V or 240 V terminals on line-
voltage models and the two 24 V terminals on low-
voltage models. See Figure 4.
Note: The voltage must be between:
- 20 VAC and 30 VAC for 24 VAC applications
- 102 VAC and 132 VAC for 120 VAC
applications
- 177 VAC and 264 VAC for 208/240 VAC
applications
c. If the voltage reading is not within the required
range, check the power source and input power
wires for problems.
2. Check for proper sensor operation.
a. Disconnect all power sources to the control.
b. Use an accurate thermometer to take a
temperature reading at the sensor location.
c. Disconnect the sensor from the control.
d. Use an ohmmeter to measure the resistance
across the two sensor leads while the sensor is at
the temperature taken in Step 2b.
e. See Figure 12 to verify that the measured
temperature and resistance conform to
established temperature and resistance values.
f. If the measured values conform to the values in
Figure 12, proceed to Step 3.
g. If the sensor’s measured resistance value is
substantially different from the expected value
for that temperature, check the sensor wiring. If
sensor wiring is correct, replace the sensor.
Figure 12: Temperature versus sensor resistance
3. Check the A421 for proper operation.
Note: Perform troubleshooting Steps 1 and 2
before you perform this step.
a. Disconnect the load from the output relay
terminals.
b. Make sure that you install the Parameter
Adjustments jumper so that you have unrestricted
access to adjust parameters.
c. Reconnect the sensor leads and supply power to
the control.
d. Replace the cover.
e. Check the control settings for proper values.
f. Press MENU until On appears. Press MENU again
to display the On value.
g. Press Down or Up to change the On temperature
above and below the sensor temperature until the
relay energizes and de-energizes.
A421 Series Standard Electronic Temperature Controls Installation Guide10

Note: If the anti-short cycle delay is set to a
value other than 0 minutes, when the control
is powered On, on the relay does not energize
until the time delay elapses.
h. If the output relay does not perform as expected,
replace the A421 Control.
i. If proper operation of the A421 Control is verified,
reconnect the load and consult the equipment
manufacturer’s instructions for troubleshooting
the controlled equipment.
Repair information
Do not attempt to repair or recalibrate the A421
Temperature Control. In case of a defective or
improperly functioning control, contact your nearest
authorized Johnson Controls/PENN distributor or sales
representative.
When you contact your Johnson Controls/PENN
distributor, have the model number of the control
available. You can find this number on the label inside the
cover of the control.
Ordering information
See Table 6 for information about a standard A421 Series
Electronic Temperature Control. See Table 7 and Table
8 to order A99 sensors, mounting hardware, and other
accessories you use to install A421 Controls. Contact your
nearest Johnson Controls or PENN distributor or sales
representative to order these products.
Table 6: A421 Series Standard Electronic Temperature
Controls selection chart
Product type Description
A421ABC-02C Line-voltage Type 1 Electronic Temperature
Control: Type 1 (NEMA), IP20 standard
enclosure for DIN rail and surface-mount
applications. Rated for 120/240 VAC. Includes
an A99BB-200C temperature sensor with 6.6
ft (2.0 m) cable.
A421ABC-03C Line-voltage Type 1 Electronic Temperature
Control: Type 1 (NEMA), IP20 standard
enclosure for DIN rail and surface-mount
applications. Rated for 120/240 VAC. Includes
an A99BB-300C temperature sensor with 9.75
ft (3.0 m) cable.
A421ABC-04C Line-voltage Type 1 Electronic Temperature
Control: Type 1 (NEMA), IP20 standard
enclosure for DIN rail and surface-mount
applications. Rated for 120/240 VAC. Includes
an A99BB-400C temperature sensor with 13.1
ft (4.0 m) cable.
A421ABC-06C Line-voltage Type 1 Electronic Temperature
Control: Type 1 (NEMA), IP20 standard
enclosure for DIN rail and surface-mount
applications. Rated for 120/240 VAC. Includes
an A99BB-600C temperature sensor with 19.5
ft (6.0 m) cable.
Table 6: A421 Series Standard Electronic Temperature
Controls selection chart
Product type Description
A421AEC-01C Line-voltage Type 4X Electronic Temperature
Control: Type 4X (NEMA), IP66 watertight
enclosure for surface-mount applications.
Rated for 120/240 VAC. Includes an
A99BB-25C temperature sensor with 9 7/8 in.
(0.25 m) cable.
A421AEC-02C Line-voltage Type 4X Electronic Temperature
Control: Type 4X (NEMA), IP66 watertight
enclosure for surface-mount applications.
Rated for 120/240 VAC. Includes an
A99BB-200C temperature sensor with 6.6 ft
(2.0 m) cable.
A421GBF-02C Low-voltage Type 1 Electronic Temperature
Control: Type 1 (NEMA), IP20 standard
enclosure for DIN rail and surface-mount
applications. Rated for 24 VAC Class 2, safety
extra low voltage. Includes an A99BB-200C
temperature sensor with 6.6 ft (2.0 m) cable.
A421GEF-01C Low-voltage Type 4X Electronic Temperature
Control: Type 4X (NEMA), IP66 watertight
enclosure for surface-mount applications.
Rated for 24 VAC Class 2, safety extra low
voltage. Includes an A99BB-25C temperature
sensor with 9 7/8 in. (0.25 m) cable.
A421GEF-02C Low-voltage Type 4X Electronic Temperature
Control: Type 4X (NEMA), IP66 watertight
enclosure for surface-mount applications.
Rated for 24 VAC Class 2, safety extra
low voltage. Includes an A99BB-200C
temperature sensor with 6.6 ft (2.0 m) cable.
Table 7: A99 Temperature Sensors selection chart
Product code1Description
A99BA-200C Positive temperature coefficient (PTC)
Temperature Sensor: Standard probe 2 in.
(5.1 cm) with 6.6 ft (2.0 m) shielded polyvinyl
chloride (PVC) cable; ambient operating
temperature range: -40ºF to 212ºF (-40ºC to
100ºC)
A99BB-25C PTC Temperature Sensor: Standard probe 2
in. (5.1 cm) with 9-7/8 in. (0.25 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A99BB-200C PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 6.6 ft (2.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A99BB-300C PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 9.8 ft (3.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A421 Series Standard Electronic Temperature Controls Installation Guide 11

Table 7: A99 Temperature Sensors selection chart
Product code1Description
A99BB-400C PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 13.1 ft (4.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A99BB-600C PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 19.7 ft (6.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A99BC-25C11PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 9 7/8 in. (0.25 m) high-
temperature silicon cable; ambient operating
temperature range: -40ºF to 248ºF (-40ºC to
100ºC)
A99BC-100C1PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 3.3 ft (1.0 m) high-
temperature silicon cable; ambient operating
temperature range: -40ºF to 248ºF (-40ºC to
120ºC)
A99BC-300C1PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 9.8 ft (3.0 m) high-
temperature silicon cable; ambient operating
temperature range: -40ºF to 248ºF (-40ºC to
120ºC)
A99BC-500C1PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 16.4 ft (5.0 m) high-
temperature silicon cable; ambient operating
temperature range: -40ºF to 248ºF (-40ºC to
120ºC)
A99BC-1500C1PTC Temperature Sensor: Standard probe
2 in. (5.1 cm) with 49.2 ft (15.0 m) high-
temperature silicon cable; ambient operating
temperature range: -40ºF to 248ºF (-40ºC to
120ºC)
A99CB-200C PTC Temperature Sensor: Extended probe
6 in. (15.2 cm) with 6.6 ft (2.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
A99CB-600C PTC Temperature Sensor: Extended probe 6
in. (15.2 cm) with 19.7 ft (6.0 m) PVC cable;
ambient operating temperature range: -40ºF
to 212ºF (-40ºC to 100ºC)
1 When any A99 Series Temperature Sensor is connected
to a standard A421 Control model, the range of displayed
temperature values is restricted to -40ºF to 212ºF or -40ºC to
100ºC.
Table 8: Accessories
Product code Description
BKT287-1R 12 in. (305 mm) long DIN rail section
BKT287-2R 36 in. (914 mm) long DIN rail section
PLT344-1R Two end clamps for DIN rail sections
A99-CLP-1 Surface mounting clip for A99B and A99C
Series Temperature Sensors
SHL10-603R Sun shield for A99B and A99C Series
Temperature Sensors
Table 8: Accessories
Product code Description
BOX10A-603R PVC enclosure for A99B and A99C Series
Temperature Sensors
WEL11A-601R Copper and brass immersion well for
applying sensor in fluid applications
TE-6300W-102 Stainless steel immersion well for applying
A99 sensors in fluid applications. A99CB
Type sensors with extended probe with this
immersion well.
Technical specifications
Table 9: A421 Series Electronic Temperature Controls
Technical Specifications
Specification Description
Power consumption 1.8 VA maximum
Supply power Low-Voltage models: 24 VAC (20 to 30
VAC), 50/60 Hz, Class 2 or Safety extra-
low voltage
Line-voltage models: 110/120 or
208/230/240 VAC, 50/60 Hz
Ambient conditions Operating: Type 1 models: -40°F to
150°F (-40°C to 66°C), 0% to 95% RH
noncondensing
Type 4X models: -40°F to 140°F (-40°C to
60°C), 0% to 95% RH noncondensing
Shipping and storage: All models: -40°F
to 185°F (-40°C to 85°C), 0% to 95% RH
noncondensing
Temperature control
range
-40°F to 212°F or -40°C to 100°C
Input signal 1,035 ohm at 77°F (25°C) for A99 PTC
Temperature Sensors
Accuracy Combined accuracy of A421 Control and
A99 sensor: ±2°F (±1°C) between 5°F and
167°F (-15°C and 75°C); diverging to ±3°F
(±2°C) at -40°F (-40°C) and ±3°F (±2°C) at
212°F (100°C)
Sensor offset range ±5ºF or ±3ºC
Enclosure material Type 1, IP20 high-impact thermoplastic
or
Type 4X, IP66 watertight, corrosion-
resistant, high-impact thermoplastic
Compliance North America: cULus Listed; UL
60730, File E27734, Vol. 1; FCC Compliant
to CFR47, Part 15, Subpart B, Class
BIndustry Canada (IC) Compliant to
Canadian ICES-003, Class B limits
Europe: CE Mark – Johnson Controls
declares that this product is in
compliance with the essential
requirements and other relevant
provisions of the EMC Directive; Low
Voltage Directive.
Australia and New Zealand: RCM,
Australia/NZ Emissions Compliant
A421 Series Standard Electronic Temperature Controls Installation Guide12

Table 10: A421 Temperature Control Output Relay
Contacts electrical ratings
A421
Agency and file UL 60730 and EN 60730
Applied AC voltage at
50/60 Hz 24 VAC 120 VAC 208 VAC 240 VAC
Horsepower LC/LNO
(LC/LNC)
-- 1 (0.25) 1 (0.3) 1 (0.5)
Full load amperes LC/
LNO (LC/LNC)
-- 16 (5.8) 9.2 (4) 8 (4.9)
Locked rotor amperes
LC/LNO (LC/LNC)
-- 96 (34.8) 55.2 (24) 48 (29.4)
Resistive amperes LC/
LNO (LC/LNC)
15 (10) 15 (10) 10 (10) 10 (10)
Pilot duty VA LC/LNO
(LC/LNC)
125 (50) 125 (125) 125 (125) 125 (125)
Table 11: UL conformity declaration information
Information Description
Purpose of control Sensing control / operating control
Construction of control Electronic independently mounted
control
Number of cycles 30,000 cycles
Method of mounting
control
Mounting screws or DIN rail
Type 1 or type 2 action Type 1.B (Micro-disconnection)
External pollution
situation
All models: A421 [ ] B: Pollution degree 3
All models: A421 [ ] E: Pollution degree 4
Internal pollution
situation
Pollution degree 2
Heat and fire
resistance category
D
Rated impulse voltage 4,000 V
Ball pressure
temperature
128°C
Cover screw torque
requirements
instruction
All models: A421 [ ] E: To maintain type
4X / IP66 rating, tighten enclosure screws
to: 10–12 in·lb
Table 12: A99B Series Positive Temperature Coefficient
Sensors Technical Specifications
Specification Description
1Sensing range1Type A99BA and A99BB: -40°F to 212°F (-40°C
to 100°C)
Type A99BC: -40°F to 248°F (-40°C to 120°C)
Reference
resistance
1,035 ohms at 77°F (25°C) and 855 ohms at
32°F (0°C)
Accuracy 0.9°F (0.5°C) between 5°F and 167°F
(-15°C and 57°C). Refer to the A99B Series
Temperature Sensors Product/Technical Bulletin
(LIT-125186) for accuracy rating outside of this
temperature range.
Sensor
construction
Probe: Stainless steel
Sensor cable
sheath
Type A99BA: Shielded PVC cable
Type A99BB: PVC cable
Type A99BC: High temperature silicon cable
Wire gauge 22 AWG
Ambient
operating
conditions
Type A99BA and A99BB: -40°F to 212°F (-40°C
to 100°C); 0% to 100% RH, condensing
Type A99BC: -40°F to 248°F (-40°C to 120°C);
0% to 100% RH, condensing
Ambient storage
conditions
Type A99BA and A99BB: -40°F to 221°F (-40°C
to 105°C); 0% to 100% RH, condensing
Type A99BC: -40°F to 266°F (-40°C to 130°C);
0% to 100% RH, condensing
Shipping weight 1.4 oz (41 g) for 6 1/2 ft (2 m) sensor
Accessories See Table 8
1 When any A99 Series Temperature Sensor is connected
to a standard A421 Control model, the range of displayed
temperature values is -40ºF to 212ºF or -40ºC to 100ºC.
The performance specifications are nominal and conform to
acceptable industry standards. For application at conditions
beyond these specifications Johnson Controls shall not be
liable for damages resulting from misapplication or misuse of
its products.
North American emissions compliance
United States
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of
the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential
installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used
in accordance with the instructions, may cause harmful interference to radio communications. However, there is no
guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference
to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to
try to correct the interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.
A421 Series Standard Electronic Temperature Controls Installation Guide 13

Canada
This Class (B) digital apparatus meets all the requirements of the Canadian Interference-Causing Equipment Regulations.
Cet appareil numérique de la Classe (B) respecte toutes les exigences du Règlement sur le matériel brouilleur du Canada.
Single point of contact
APAC Europe NA/SA
JOHNSON CONTROLS
C/O CONTROLS PRODUCT
MANAGEMENT
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DISTRICT
WUXI JIANGSU PROVINCE 214028
CHINA
JOHNSON CONTROLS
WESTENDHOF 3
45143 ESSEN
GERMANY
JOHNSON CONTROLS
507 E MICHIGAN ST
MILWAUKEE WI 53202
USA
For more contact information, refer to
www.johnsoncontrols.com/locations.
© 2019 Johnson Controls. All rights reserved. All specifications and other information shown were current as of document revision and
are subject to change without notice.
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