Aprilaire 8553 - Manual (Page 29)

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In Case Of Power Failure
The Model 8553 thermostat does not require a battery. If the power goes out the letters “AC” appear
on the display indicating power is not being supplied to the thermostat. “AC” will remain on the
display for up to approximately 1 hour after the power goes out. During the period that the power is
off, the heating/cooling system will not operate.
This thermostat is equipped with a continuous memory feature which does not require any battery.
The thermostat will never lose what has been programmed regardless of the length of the power
outage. If the thermostat has been set to “Hold” a particular temperature and the power fails, the
thermostat will maintain the hold temperature when the power is restored.
After a period of 1 hour without power the clock will need to be reset. The clock will default to
12:00 AM. Refer to the Programming Instructions to reset the clock.
110-790B 7/11/01 3:11 PM Page 29