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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–50
Code No. LIT-1900935
A421 Series Electronic Temperature
Control with Off-Cycle Defrost
A421 Series Electronic Temperature Controls with Off-Cycle Defrost
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.
A421 Controls with Off-Cycle Defrost
(A421ABD and A421AED models)
provide off-cycle defrost control with
user-configurable defrost cycle duration and
frequency.
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 Off-Cycle Defrost 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.
• integrated off-cycle defrost timer (defrost
control models only) shuts off the
refrigeration system for a user-defined
defrost time interval at a user-defined
frequency. This eliminates the cost and
time to install a separate defrost timer in
many refrigeration 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
(NEMA)/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.
Single-Stage Electronic Temperature Controls