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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. www.johnsoncontrols.com
R–53
Code No. LIT-1900936
A421 Series Electronic Temperature
Control with Integral Cycle Timer
A421 Series Electronic Temperature Controls with
Integral Cycle Timer
Description
The A421 Series Electronic Temperature
Controls are single-stage controls with a
single-pole, double-throw (SPDT) output
relay, a bright backlit LCD, 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. The
A421 Series Controls have simple On and Off
temperature settings for heating or cooling, an
adjustable anti-short cycle delay, and a
temperature offset function.
The control range is -40 to 212°F
(-40 to 100°C) for standard models. Models
with a control range of -40 to 248°F
(-40 to 120°C) are available in quantity orders.
The controls feature remote sensing capability
and interchangeable sensors. The
A421 Controls are available in either
Type 1 (NEMA)/IP20 high-impact plastic
enclosure suitable for surface or DIN rail
mounting or Type 4X (NEMA)/IP66 watertight,
corrosion-resistant surface mount enclosures.
The A421 Controls with Integral Cycle Timer
provide On/Off control of ventilation fans in
agriculture applications, warehouse and
storage facilities, and other ventilation
application that require air-exchange based on
temperature or a ventilation schedule with a
user-defined On-time and Off-time cycle.
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 with Integral Cycle Timer fails to
operate within its specifications, replace the
unit. For a replacement A421 Control, contact
the nearest Johnson Controls®
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 and timed ventilation control
(integral cycle timer models only) enables
you to set up timed ventilation or makeup
air cycles independent from temperature
controlled cycles. This eliminates the cost
and time to install a separate interval timer
in ventilation and makeup air 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 NEMA 1/IP20 or
NEMA 4X/IP66 watertight,
corrosion-resistant enclosures increase
application options, allowing surface and
snap-fit DIN rail mount, or watertight
surface mount.
Single-Stage Electronic Temperature Controls