A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Instructions
13
Restricting User Adjustment
You can restrict user adjustment of the A421 control to
either just OFF value (control band) adjustment within
a defined range (Figure 12) or no user adjustment at
all.
You set the A421 control into the restricted adjustment
mode by positioning 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 following behavior is enforced:
• The restricted temperature adjustment range is
defined by the selected High Temperature Stop
(HtS) and Low Temperature Stop (LtS) values.
• The control band (differential) is defined by the On
and OFF values, and the control band between On
and OFF remains fixed (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.
Setting the Control to Restricted Adjustment Mode
To set up the restricted adjustment feature:
1. Ensure that the A421 is not in the restricted mode
(the jumper is positioned on both pins). See
Figure 13.
2. Select the OFF and On values that define the
application’s required control band (Figure 12).
Figure 11: Starting and Stopping a dFt: Behavior Using SdF Parameter and Momentary Contact Switch
Figure 12: Adjustment Behavior in
Restricted Adjustment Mode
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