Nest Thermostat defrost cycle on OB wire

[DaveInTheDesert]

Hello, just had our Nest 3rd Gen Learning thermostat installed. Have been assured that the OB wire will let Nest control the defrost cycle on a 2-stage all electric heat pump system. Is this correct? All control boards in the hvac system are fairly new and programmable by the install company.

[Markjosephp]

Hello DaveInTheDesert,

I'm sorry for the late reply, and congratulations on your new Nest Learning thermostat installation!

Regarding the OB wire and its role in controlling the defrost cycle on your 2-stage all-electric heat pump system, it's important to note that the functionality may vary based on the specific configuration of your HVAC system.

Typically, the O/B wire is used for reversing valve control, which is essential for the heat pump to switch between heating and cooling modes. In the case of the defrost cycle, it usually involves the heat pump temporarily shifting into a cooling mode to melt any accumulated frost on the outdoor unit. Given that your HVAC system's control boards are fairly new and programmable, it's advisable to consult your HVAC system's documentation. Additionally, reaching out to the installation company for clarification or assistance can provide more accurate and system-specific information.

Let us know if you have more questions.

Best regards,
Mark