Applications
You can use the A421 Control to manage a
wide range of single-stage refrigeration or
HVAC equipment. Sample temperature control
applications include:
• On/off control chillers
• Chiller pump control
• Cooling control
Features and benefits
Control front panel LCD
Displays the temperature, parameters, and status.
You can adjust the backlight intensity for ambient
light conditions. Custom icons display the system
and control status.
Basic and Advanced programming menu
Provides two levels of parameter adjustment and
control. You can set up advanced features in one
menu and adjust basic parameters in the other
menu.
Off-Cycle defrost
Shut off the refrigeration system for defined defrost
time interval and frequency. You can also start or
stop a manual only defrost off-cycle.
On/Off temperature adjustment
Select the temperature values at which the relay
turns on and off and automatically define the mode
of operation.
Switch-activated temperature setback
Shift the On/Off temperature by an adjustable
setback. When a user-supplied switch closes the
binary input control circuit, temperature setback is
enabled.
Adjustable anti-short cycle delay (ASd)
Select the minimum time the output relay
remains off before the next on-cycle. By selecting
this minimal time, you can avoid short cycling,
hard starts, and nuisance overload outages on
compressors and other inductive applications.
Adjustable sensor offset
Adjust the displayed temperature to the actual
sensed temperature.
Optional restricted adjustment mode
Restrict the On/Off adjustment to your defined
temperature range.
Sensor failure mode
Run the control continuously in the event of a
sensor or sensor wire failure or to shut it down.
Backlight brightness level
Adjust the brightness of the backlighting of the LCD
screen. The backlight brightness level is applied
during normal operation. When you set up or adjust
the parameters, the LCD automatically goes to the
brightest level.
Repair information
Do not attempt to repair or recalibrate the A421
Series Electronic Temperature Control. In case
of a defective or improperly functioning control,
contact your nearest authorized Johnson Controls
®
or PENN
®
distributor or sales representative.
When contacting your Johnson Controls or PENN
distributor, have the model number of the control
available. This number can be found on the label
inside the cover of the control.
Ordering information
Contact your nearest Johnson Controls or PENN
distributor or sales representative to order sensors,
mounting hardware, and other accessories to
install the A421 Controls. Contact your local
Johnson Controls or PENN representative for
more information on options available for high-
volume purchase models with specific application
requirements.
2 A421 Series Electronic Temperature Controls with Off-Cycle Defrost Catalog Page