Johnson Controls – PENN A421ABD-02C Series Electronic Temperature Controls with Off-Cycle Defrost

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 120 VAC and 240 VAC models.
The A421 Control with Defrost allows you to set up regular, passive defrost periods of 1 to 99 minutes. The defrost interval can range from 2 to 24 hours, or be set to 0 (no defrost interval). You can also start or stop a defrost off-cycle in two ways: using the three-button touchpad on the Advanced Menu or connect a momentary switch to the Binary Input (BIN).

The A421 also provides 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-12012219) for important product application information.

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.
• Off-Cycle Defrost allows you to shut off the refrigeration system for defined defrost time interval and frequency. You can also start or stop a manual only defrost off-cycle.
• Off-Cycle Defrost allows you to 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 allows you to select the temperature values at which the relay turns On and Off, which automatically defines the mode of operation.
• Switch-Activated Temperature Setback allows you to 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 allows you to select the minimum time the output relay remains off before the next oncycle. 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 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 run the control continuously in the event of a sensor or sensor wire failure or to shut it down.
• Backlight Brightness Level allows you to 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.

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

• on/off control chillers
• chiller pump control
• cooling control