Product Overview

The performance specifications are nominal and conform to acceptable industry standards. For applications at conditions beyond these specifications, consult the local Johnson Controls office.
Johnson Controls, Inc. shall not be liable for damages resulting from misapplication or misuse of its products. © 2015 Johnson Controls, Inc.
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R–44
Code No. LIT-1900933
A421 Series Electronic Temperature
Control
A421 Series Electronic Temperature Controls
Single-Stage Electronic Temperature Controls
Description
The A421 Series Electronic Temperature
Controls are single-stage controls with a
single-pole, double-throw (SPDT) output
relay.
A421 Controls feature a bright backlit LCD
with adjustable brightness and a three-button
touchpad interface that can be set up to
restrict user adjustments. An LED indicates
the output relay's On/Off status. Standard
A421 Series control modules 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 to 212°F or -40 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 or in Type 4X (NEMA), IP67 (CE)
watertight, corrosion resistant surface mount
enclosures.
Refer to the A421 Series Electronic
Temperature Controls Product Bulletin
(LIT-12011972) for important product
application information.
Applications
The A421 Electronic Temperature Control can
be used to control a wide variety of
single-stage refrigeration or HVAC equipment.
Sample temperature control applications
include:
• temperature monitoring and alarming
• on/off control of boilers and chillers
• boiler and chiller pump control
• heating and cooling control
• floating temperature control of damper and
valve actuators
• cooling tower fan control based on water
temperature
• supply, makeup, and mixed air temperature
control
• temperature actuated valve control
• supply and makeup air damper and fan
control
• condenser fan control based on condenser
temperature
• parameter adjustment restriction allows
you to lock the control’s setup parameters
and restrict user adjustments to just the On
and Off temperature setpoint values within
your defined setpoint adjustment range.
• low- and line-voltage control models
provide industry standard control voltage
options for most refrigeration and HVAC
control applications.
Repair Information
If the A421 Series Electronic Temperature
Control fails to operate within its
specifications, replace the unit. For a
replacement A421 Control, contact the
nearest Authorized
Johnson Controls/PENN® Distributer or Sales
Representative.
Features
• easy-to-read, bright, adjustable backlit LCD
screen displays the temperature,
parameters, and status clearly and allows
you to adjust LCD brightness for the
ambient light conditions. Custom icons on
the display provide visual cues on system
and control status.
• basic and advanced programming menus
allow you to easily set up your control
application on the LCD using a simple
three-button touchpad interface.
• adjustable On and Off temperature
setpoints enable easy to set up cooling or
heating control applications on the
three-button touchpad, eliminating the
need to remove the cover and reposition
jumpers for reverse or direct control
actions.
• high and low temperature setpoint
adjustment stops allow you to set up your
application for your desired range of
adjustment and restrict user adjustment to
just the desired temperature adjustment
range.
• displayed temperature offset allows you to
adjust the displayed temperature to the
actual sensed temperature in applications
where the resistance error in long sensor
cable leads cause a deviation in the
displayed temperature from the actual
sensed temperature.
• adjustable anti-short cycle delay keeps the
output relay Off after the Off setpoint is
reached for a user-defined time delay,
which helps avoid short cycling, hard starts,
and nuisance overload outages on
compressors and other inductive
applications.
• temperature setback/offset control enables
the control to shift the On and Off setpoint
values by a user-defined offset when an
external switch closes the binary input
control circuit. Using a switching timer
enables you to set up occupied/unoccupied
temperature setback schedules for your
applications.
• high-impact, thermoplastic Type 1/IP20 or
Type 4X (NEMA)/IP66 watertight,
corrosion-resistant enclosures increase
application options, allowing surface and
snap-fit DIN rail mount, or watertight
surface mount.