A421AEC-01C | Single Stage Temp Controller with Sensor, 120/240VAC, NEMA4X, 9
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Brand: Johnson ControlsSKU: A421AEC-01C

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A421AEC-01C | Single Stage Temp Controller with Sensor, 120/240VAC, NEMA4X, 9" lead, -40 to 212F, HTG/CLG | Johnson Controls

Johnson Controls | A421AEC-01C
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Details for A421AEC-01C


Single Stage Temp Controller with Sensor, 120/240VAC, NEMA4X, 9" lead, -40 to 212F, HTG/CLG


The A421 Series controls are single stage, electronic temperature controls with a single-pole, double-throw (SPDT) output relay. The controls feature an adjustable backlit LCD for viewing the temperature and status of other functions, and a three-button touchpad for setup and adjustment. An LED indicates the On/Off status of the output relay.

The A421 controls are available in low voltage 24 VAC and high voltage 120 or 240 VAC models, which provide options for most refrigeration and HVAC applications.

The A421 controls provide heating or cooling control, sensor offset, temperature setback, adjustable anti-short cycle delay, and a restricted user adjustment mode. The temperature units can be displayed in °F or °C. The temperature adjustment range is -40 to 212°F or -40 to 100°C.

The A421 controls are available in Type 1, IP20 high-impact plastic enclosures suitable for surface or DIN rail mounting and Type 4X, IP66 watertight, corrosion-resistant surface mount enclosures.

Refer to the A421 Series Electronic Temperature Controls Product Bulletin (LIT-12011972) for important product application information.


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
  • cooling tower fan control based on water temperature
  • supply, makeup, and mixed air temperature control
  • temperature actuated valve control

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/PENN® Distributor or Sales Representative.

When contacting your Johnson Controls/ 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/ PENN Distributor or Sales Representative to order sensors, mounting hardware, and other accessories used to install A421 controls.

Contact your local Johnson Controls/PENN representative for more information on options available for high-volume purchase models with specific application requirements.

Features and Benefits

  • Control Front Panel LCD – displays the temperature, parameters, and status and allows you to 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 setup, allowing you to set up advanced features in one menu and easily adjust basic parameters in the other menu.
  • On/Off Temperature Adjustment – allows you to select the temperature values at which the relay turns On and Off, which automatically defines the Heating or Cooling mode of operation.
  • Switch-Activated Temperature Setback – allows you to shift the On/Off temperature by an adjustable setback value. When a user-supplied switch closes the binary input control circuit, the control operates at the defined setback temperatures.
  • Adjustable Anti-Short Cycle Delay – allows you to select the minimum time the output relay remains off before the next on cycle; avoiding short cycling, hard starts, and nuisance overload outages on compressors and other inductive applications.
  • Adjustable Sensor Offset – allows you to adjust the displayed temperature to the actual sensed temperature.
  • Optional Restricted Adjustment Mode – allows you to restrict the On/Off adjustment to your defined temperature range.
  • Sensor Failure Mode – allows you to select the relay On/Off state in the event of a sensor or sensor wire failure.
  • Backlight Brightness Level – allows you to adjust the LCD backlight intensity


Item Number A421AEC-01C
Brand Johnson Controls
Housing NEMA4X
Type Temperature Controller
Voltage 120/240VAC

Documents and manuals

Johnson Controls A421AEC-01C Documents

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