Carrier A07051 Installation Instructions Manual page 20

Homeowners Guide for details. If batteries are installed and the thermostat is
operated from 24VAC power, battery operation will occur only when 24VAC
power is not present. The changeover between 24VAC power and battery power
is automatic.
Display Lighting
The display has two levels of lighting, high level and low level. High level
lighting comes on for 10 seconds when the door is opened and/or buttons are
being pressed with 24VAC and with batteries. Low level lighting is only
available if the thermostat is operated from 24VAC. It is not available with
batteries. The low level can be selected (see Option 18) for continuous backlight.
Door Switch
When the door is opened, the display changes from its normal operation view.
The large temperature display disappears so it will be available for other user
functions. If the door is left open for 3 minutes, the display reverts to normal
operation.
Mounting Options
For those installations requiring it, mounting hole locations for the
programmable model are spaced to fit either a horizontal or vertical junction box.
Mounting hole locations for the non- -programmable are spaced to fit a horizontal
junction box.
Defrost Operation
In a HP installation with the "O" selection of Option 10, the thermostat allows all
defrost cycles to run to completion before turning off the compressor. It does this
by sensing a 24VAC signal on the O line which it did not produce. This occurs
while the HP is defrosting. As long as this O signal is present, the thermostat will
keep the Y output on, even if it is satisfied, thus allowing the defrost cycle to
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