Ok, the Nest Learning Thermostat 3rd generation can handle two fan speeds. The way you have them in your old thermostat has a White wire in GH and a green wire in GL. The second green wire is in W. The B wire is your Common. If you are confident of the wires and where you put them in your old thermostat base, here is what your input to the Google Nest Configurator.
R-Red Wire
C-Blue Wire (the wire on B)
GL-Green Wire
GH-White Wire
Y-Yellow Wire
W-Green Wire
Again, you need to upgrade to a Nest Learning Thermostat 3rd Generation in order to have support for two fan speeds. The Nest thermostat you showed a picture of will not support dual fan speeds. Now the configuration of your fan speed will be as follows, GH is for cooling with the air conditioner, and the GL is when you’re running the heater for heating the house. If it is not too much trouble, would like to get a picture of your furnace manufacturers label, which shows the model number, and a copy of the outdoor unit manufacture label that shows again the model number. It is not often that you find a thermostat that is controlling the blower speeds for heating and cooling separately. Generally the air handler with the heater in it, has a control board and that control board looks at the signaling wires coming in, specifically, W and G, and select the appropriate speed for the blower fan.
Ask any additional questions you have.
Ken, The AC Cooling Wizard
NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
