Gen 4 two speed fan only using low speed for heat

[FloJoe]

I have a new Rheem heat pump and air handler that has a two speed fan for both heat and cool. It worked properly with the original thermostat (Honeywell Pro Series). With the Nest gen 4 the fan only runs on low. How do I fix this? 

Wiring

Y1 - Heat/Cool.  Y2 - Heat/Cool 2

G - Fan.  OB - Heat Pump. Rc- Power

C - 24v common

[CoolingWizard]

@FloJoe ,

what you have is a two stage compressor. Y1 is stage-1 and Y2 is stage-2. You have only 1 G wire so your fan speed is actually controlled by the control board in the air handler and not the thermostat. More than likely your system is using an ECM type or X13 type blower motor. These types of motors, provide either a constant torque of airflow or a constant volume. In all likelihood as well when you switch to Y2 compressor, speed the fan speed will change.  Again. This change will be performed by the control board in the air handler.  

AC Cooling Wizard

[FloJoe]

I don’t understand. The fan worked properly with the Honeywell thermostat. 

[CoolingWizard]

@FloJoe 

upload the picture of the wiring of the old thermostat before you removed it. 

AC Cooling Wizard

[FloJoe]

https://imgur.com/a/EaGbjgU

[CoolingWizard]

@FloJoe ,

your old thermostat only had a single fan wire, a G wire. as I stated, it’s the internal control board of your air handler that controls the speed of the fan and not the thermostat. 

AC Cooling Wizard.