Carrier Transicold Supra 550 Operator's Manual page 14

Setpoints of -22°F to +89°F (-30°C to +32°C) may be entered via
the keypad. The controller always retains the last entered setpoint
in memory. If no setpoint is in memory (i.e. on initial startup), the
controller will lock out the run relay and flash "SP" on the left hand
display until a valid setpoint is entered. The setpoint may be
changed up or down in 1° increments by pressing and releasing
either the UP ARROW or DOWN ARROW key.
You cannot change setpoint when unit is in Pretrip or when viewing
Unit Data or Functional Parameters.
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