Mitsubishi Electric PAR-W21MAA Instruction Book page 14

<To Turn Off the Auto Off Timer...>
Hold down the Timer ON/OFF button 9 for 3 seconds, so that "Timer Off"
appears (at 6) and the timer value (at 7) disappears.
Alternatively, turn off the unit itself. The timer value (at 7) will disappear from the
screen.
<To Turn On the Auto Off Timer...>
Hold down the Timer ON/OFF button 9 for 3 seconds. The "Timer Off" indication
disappears (at 6), and the timer setting comes on the display (at 7).
Alternatively, turn on the unit. The timer value will appear at 7.
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