Figure 11: Starting and stopping a dFT: behavior
using SdF parameter and momentary contact switch
Restricting user adjustment
You can restrict user adjustment of the A421 Control to the OFF value control band adjustment
within a defined range (Figure 12) or no user adjustment at all.
To set the A421 Control to the restricted adjustment mode, position the P1 jumper located on the
circuit board next to the TB3 terminal block. See Setting the control to Restricted Adjustment mode.
Note: Setting the A421 Control up in the Restricted mode prevents casual users from over-
adjusting the control in your application, or from inadvertently changing the mode of
operation from cooling to heating or heating to cooling (by over-adjusting the On value or OFF
value).
When the A421 Control is set up in the restricted adjustment mode, the controller enforces the
following behavior:
• The selected HtS and LtS values define the restricted temperature adjustment range..
• The On and OFF values define the control band differential, and the control band between On
and OFF remains fixed and not adjustable.
• Only the OFF value can be adjusted, the control band remains fixed, and the On value
automatically shifts equal to the OFF value adjustment.
• The OFF value can only be adjusted to values that maintain the entire control band within the
restricted temperature adjustment range defined by HtS and LtS. See Figure 12.
• The basic and advanced menus are not available. Only the Restricted Adjustment mode menu is
available and only the OFF value can be adjusted. See Figure 14.
19A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide
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