Google Nest Learning Thermostat 4th Gen Installation And Configuration Manual page 78

Power requirements and details
Battery - The preferred voltage of the stat is 3.9v. If the thermostat drops below 3.8v, it will enter a "Power Saver"
mode where some features and functions will be disabled. You will see this on the thermostat under the Power
Info settings page. If the voltage drops below 3.6v, the thermostat will disconnect from Wi-Fi and if it drops below
3.7v, other features such as the Wake On Approach of the thermostat will be disabled.
Appropriate power readings - Can be found on the thermostat under Settings> Equipment> Power Info
Value Found on Thermostat
VIN (Voltage input)
Iin (Current Intensity input)
Note: These values are not RMS voltage. You can divide the Voc or VIN by 1.414 to get an approximate RMS
voltage the stat is reading. Always confirm voltage with a multimeter.
Iin readings and what they mean
Iin is the input current limit the thermostat is using now. The letter next to the Iin value indicates the method of
power sharing. The value should be above 20mA for full functionality. Some of the letters may be combined to
provide more detail; for example, WA means that we are actively sharing power from the W wire.
Note: The thermostat will power share less frequently during the first 5 minutes of a call or heating or cooling
when in the A or T mode.
SY - Improved power sharing function being used on the Y wire.
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W - W is used for power sharing.
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Y - Y is used for power sharing.
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P - Drawing power from the Nest Power Connector. Note: this will confirm the Power Connector is installed
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and functioning correctly.
T - Taco valve detected and utilizing a specific power sharing method for Wax Actuated Valves.
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A - Sharing power from an active wire, either W or Y.
●
PS values and what they mean.
PS values are stats for the available methods of power sharing. These will provide more details, but will likely only
be relevant when calling Pro Support.
C - Maximum current draw on C-wire. Note: this will verify C wire functionality.
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Y, W, or YW - Maximum current draw on Y, W or Y+W wires when the thermostat is not activating them.
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YA or WA - Maximum current draw on Y or W wires when the thermostat is activating them.
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YP or WP - Metric to assess Power Connector presence on Y/W wires (greater than 12 typically means
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Power Connector is present, but there are other conditions that also need to be met for it to be detected).
With Common or Power
Connector
24 to 42V
150 to 300 mA
Troubleshooting - Power Sharing
Without Common or Power Connector
24 to 42V
20 to 300 mA
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