Parameter codes and modes of operation - PENN Controls - A421ABD - A421AED - Electronic Temperature Control - A421 Off‐Cycle Defrost Model

A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide

Product name
A421 Off‐Cycle Defrost Model
Document type
Installation Guide
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Revision date
Relay Off temperature (OFF)
Select the temperature at which the output relay de-energizes, the LC to LNO relay contacts open (cutout), and the green LED goes off. The range of usable temperature values is -40°F to 212°F (-40°C to 100°C) in 1° increments.
Relay On temperature (On)
Select the temperature at which the output relay energizes, the LC to LNO relay contacts close (cut in), and the green LED lights. The range of usable temperature values is -40°F to 212°F (-40°C to 100°C) in 1° increments.
Heating or Cooling mode of operation

When you select your required On and OFF values, the control automatically determines the mode of operation and displays the proper mode icon on the Main screen.

Note: The A421 Series Controls do not have jumpers for setting up the heating or cooling mode.
The heating or cooling mode is determined by the On and OFF value relationship as follows:
  • OFF > On = Heating mode = Flame icon
  • OFF < On = Cooling mode = Snowflake icon

    Important: During normal operation, adjusting just the On value or just the OFF value on the A421 Control changes the differential between On and OFF, and can potentially change the mode of operation from heating to cooling or cooling to heating. To maintain a constant differential between on and off, you must adjust both the On and OFF values by an equal number of degrees, or set up the control in the Restricted Adjustment mode. See Restricting user adjustment.
Anti-Short Cycle Delay (ASd)

Select the minimum time that the output relay remains off (de-energized) before the next on-cycle can start. The ASd interval overrides any load demand (On) and does not allow the output relay to go on until the selected ASd interval has elapsed. See the following figure.

Figure 1. Anti-short cycle delay (ASD)

Anti-short cycle delay is typically used for refrigeration applications so that the system pressure can equalize before restarting the compressor.

Note: When the ASd value is greater than 0, the delay interval initiates every time that the A421 Control powers on and every time that an off-cycle begins. When the ASd interval is activated, the temperature sensed at the A99 sensor and the parameter code ASd flash alternately on the LCD. You can set the ASd interval from 0 minutes to 12 minutes, in 1 minute increments.
Sensor Failure mode (SF)
Select whether the control’s output relay operates as energized or de-energized in the event of a sensor or sensor wiring failure. When the control detects a sensor circuit failure, the output relay operates in the selected sensor failure mode. The LCD flashes SF and OP if the sensor circuit is open or SF and SH if the sensor circuit is shorted.
Temperature Units (Un)

Select the preferred temperature scale for your application. Select either the Fahrenheit (°F) or Celsius (°C) temperature scale.

Note: After you change the temperature units value (Un), confirm that the temperature values for the other parameter codes are still correct for your application.
Low Temperature Stop (LtS)
Select the lowest temperature value that the On/OFF control band can be adjusted to when control adjustment is restricted.
High Temperature Stop (HtS)
Select the highest temperature value that the On/OFF control band can be adjusted to when control adjustment is restricted.
Restricted Adjustment mode

The HtS and LtS values define the restricted adjustment temperature range and are enforced only when the A421 Control is set to the restricted adjustment mode (Figure 1). See Restricting user adjustment.

Note: It is best practice to leave HtS and LtS at their default values, unless you intend to use the restricted adjustment mode.
Note: If you use the Temperature Setback feature in the Restricted Adjustment mode, the effective On and OFF setback values (On + tBs and OFF + tBs) can be greater than the selected HtS value or less than the selected LtS value.
Temperature Setback (tSb)
Select a temperature value for setting back the On and OFF temperature values. When a user-supplied switch between the BIN and COM terminals closes, note the following changes:
  • The Main screen displays BIN in the upper-right corner of the LCD.
  • The temperature setback feature is enabled and the control uses the effective On and OFF setback values (On + tSb and OFF + tSb) to control the relay.
Note: The control displays only the original On and OFF values in the normal and setback modes. The effective setback On and OFF values (On + tSb and OFF + tSb) never display on the control LCD.

The temperature setback adjustment range is from -50°F to 50°F (-30°C to 30°C). Typically, heating applications require a negative temperature setback (tSb) value, and cooling applications require a positive value.

Sensor Offset Adjustment (So)
Sensor offset allows you to compensate for any difference between the displayed temperature value and the temperature sensed at the A99 sensor. Select a temperature value to offset the temperature displayed on the LCD from the temperature sensed at the sensor. The sensor offset adjustment range is from -5°F to 5°F (-3°C to 3°C) in 1° increments.
Backlight Brightness Level (bLL)
The backlight brightness level feature allows you to adjust the LCD backlight intensity. At level 0 the backlight is off. Level 10 is the brightest backlight setting and the system default. The selected backlight brightness level is applied to the LCD during normal operation. When you enter the programming menus to set up the control or press any key, the LCD automatically goes to the brightest level. If you do not press a key for 30 seconds, the main screen displays and the backlight setting reverts to the selected brightness level.
Defrost Cycle Time (dFt)
Select the time in minutes that the defrost cycle overrides On and keeps the relay Off. The dFt value can be between 1 minutes and 99 minutes. When the defrost cycle is On, the control is NOT running and the LCD displays the following screens: dEF (defrost mode), minutes remaining, and the temperature at the sensor. When the dFt is complete, the control returns to normal (On/Off cycle) operation.
Defrost Interval (dI)

Select the time in hours between the start of a defrost cycle and the next defrost cycle. The dI value can be set to 0 or 2 hours to 24 hours.

Note: At the initial power On, the defrost interval (dI) does NOT have a defrost cycle (dFt). The subsequent defrost intervals begin with the selected dFt.

Setting the dl value to 0 eliminates regular or timed defrost cycles. You can still start or stop a defrost cycle by setting the SdF parameter or by using the binary input.

Start or Stop Defrost Cycle (SdF)

The Start/Stop Defrost Cycle parameter allows you to start a defrost cycle, when the control is in normal (On/Off cycle) operation, or stop a defrost cycle when the defrost cycle is On.

Change to the SdF value to 1 to start a defrost cycle. Or, change the value to 0 to stop the defrost cycle, and return to normal (On/Off cycle) operation.

Binary Input modes (bIn)

The BIN mode allows you to select how the A421 Control operates when a user-supplied binary switch connected across BIN and COM on the TB3 terminal block is used with the control.

Set the BIN parameter to 0 to use the temperature setback feature. Set the value to 1 and connect a user-supplied momentary contact switch to start or stop a defrost cycle.

Table 1. Standard parameter setup codes, descriptions, range of values, and default values
Parameter code Parameter description (menu) Range of usable values Factory default value 1
Un Temperature Units (Advanced only) ºF or ºC ºF
OFF Relay Off Temperature (Basic, Advanced, and Restricted)

-40ºF to 212ºF

(-40ºC to 100ºC)

On Relay On Temperature (Basic and Advanced)

-40ºF to 212ºF

(-40ºC to 100ºC)

ASd Anti-Short Cycle Delay (Basic and Advanced) 0 minutes to 12 minutes 1 minute
tSb Temperature Setback (Advanced only)

-50ºF to 50ºF

(-30ºC to 30ºC)

So Sensor Offset Adjustment (Advanced only)

-5ºF to 5ºF

(-3ºC to 3ºC)

HtS High Temperature Stop (Advanced only)

-40ºF to 212ºF

(-40ºC to 100ºC)

LtS Low Temperature Stop (Advanced only)

-40ºF to 212ºF

(-40ºC to 100ºC)

SF Sensor Failure Action (Basic and Advanced) 0 = output relay de-energized

1 = output relay energized

1 output relay energized
bLL LCD Backlight Brightness Level Adjustment (Advanced only) 0 to 10; 0 = backlight off, 10 = brightest backlight setting 10 (brightest backlight)
dFt Defrost Cycle Time (Advanced only) 1 minutes to 99 minutes 30 minutes
dI Defrost Interval (Advanced only) 0 or 2 hours to 24 hours 8 hours
SdF Start or Stop Defrost Off-Cycle (Advanced only) Change 0 to 1 to Start a new Defrost Cycle

Change 1 to 0 to Stop a Defrost Cycle

bIn Binary Input Mode (Advanced only) 0 = Temperature Setback Mode

1 = Start Defrost Cycle Mode

1 The default values for general application A421 models are shown. OEM A421 models may have different default values.