topic Re: Dual Fuel Nest Setup in Nest Thermostats

Dual Fuel Nest Setup

Jenn8 — Mon, 09 Mar 2026 15:33:52 GMT

I am trying to install my Nest E thermostat. Currently, when the thermostat calls for cooling, the fan comes on but the compressor does not. The compressor and fan are functionally fine and ran appropriately with the previous thermostat, so it has to be a setting/setup issue. Here's what I have - any help is appreciated!

Nest Thermostat E, GA01334-CA
Dual fuel: heat pump cooling only, gas boiler heat only
Compressor ran before factory reset, not after
Y confirmed connected on wiring screen
Current Equipment settings: Forced air, Each cycle, O wire, dual fuel breakpoint 50°F

Re: Dual Fuel Nest Setup

CoolingWizard — Tue, 10 Mar 2026 06:27:15 GMT

@Jenn8

You need to decide what you really want to do is never use the heat pump for heat. If this is the case you will need to do some special wiring in your air handler/furnace. Please keep this in mind, if you have a type O heat pump, it by default is a Heater. The OB wire must be energized to make the heat pump be an air conditioner. Let me know what you want your HVAC equipment to operate as designed or if you want make the heat pump strictly cool and gas furnace be your only source of heat in you home.
If you really want the duel fuel for heat then you change the heat pump break over 25°F and not 50.

The Cooling Wizard

Re: Dual Fuel Nest Setup

Jenn8 — Tue, 10 Mar 2026 07:21:11 GMT

We want to never use the heat pump for heat, and we're fine with manually switching from heat to cool seasonally. The original Honeywell stat had the boiler hooked up as "emergency heat" so we have that turned on all winter. Can the nest be configured the same?

Re: Dual Fuel Nest Setup

CoolingWizard — Tue, 10 Mar 2026 07:46:06 GMT

@Jenn8 ,

First turn off the power to the Furnace. In order to use a Heat Pump for only Cooling you must remove the OB wire on the Nest Thermostat base.
Next you need to go to the Furnace / Air Handler. There you will find the Integrated Furnace Control-board (IFC). Locate the colored wire on the thermostat cable that was connected to OB. This specific wire will be attached to the cable coming from the outdoor unit. Locate that wire, disconnect from the wire going outside. Now take that wire going outside and attach with the Y or Y1 wire on the Y terminal on the IFC. Now anytime the thermostat calls for cooling, the Nest Thermostat will energize Y1 and since the OB wire is also on Y1, it energize the changeover valve and operate the type O heat pump as an Air Conditioner. Make sure the Furnace wire that is probably on W2/aux is moved to W1 on the Nest Thermostat base.

Now turn the power to furnace back on. Let’s do a reboot on the Nest Thermostat. Press and hold the ring Nest Display for 10 seconds until the display goes blank, Release. When the Nest reboots it will check the wires and change the configuration to an Air Conditioner with Gas Heat.

The Cooling Wizard