Google Nest Thermostat 4th generation

[JustGarth]

Does anyone have any advice on wiring my brand new Google nest thermostat 4th generation? 

[CoolingWizard]

@JustGarth ,

your current system is a heat pump, which has both auxiliary heat and emergency heat capability. Your wires that you see, including the little blue jumper between RH and RC, you can ignore that jumper wire. Now as for the rest of them. The RED wire will go to the NEST RC. the YELLOW wire will go to the NEST Y1. The GREEN wire will go to the NEST G. The black wire will go to the NEST E (emergency heat, the WHITE wire will go to the NEST W2/AUX, the Orange wire will go to the NEST OB. And the blue wire will go to the NEST C.

AC Cooling Wizard

[JustGarth]

Thank you for the thorough response to my request for assistance. It’s a good thing I can disregard the jumper wire. As far as I know, my new thermostat doesn’t have the E for the black wire. Do you mean the * ?

[CoolingWizard]

@JustGarth ,

the Google Nest Learning thermostat is fully progrmable where your current thermostat is not.  So the old thermostat has a terminal label W1/E.  So hang on because here comes some HVAC education.

Each of the labeled terminals of a thermostat are provide a specific function.

one. The R terminals, which are R, RC and RH are for power input. The power that controls your typical HVAC system is AC power at 24 V. Some systems are separate heating from cooling and that’s why you have an RC and an Rh. A conventional system like a heat pump only uses one terminal for power typically we assign it to RC.

The next wire is the Y terminal. You have, Y1, and Y2. When you have a high efficiency air-conditioning condensing unit outdoors, you would have Y1 and Y2 for stage one cooling and stage two cooling.

the G terminal is for the indoor blower fan. On your thermostat you typically have a auto/on switch. An auto mode the thermostat controls the blower fan, if you switch it to on you manually can turn on the indoor blower fan.

the next terminals are W1, and W2. This is for stage one and stage two heating typically. In the case of a heat pump, the W1 wire is typically repurposed as the emergency heat, and the W2 is repurpose as auxiliary heat. I’m going to guess, since you have auxiliary heat and emergency heat capability that you live in a very cold part of the country. 

The next heat pump wire is the O and the B terminals. Heat pumps are manufactured as either one of two types. Type O heat pumps are by default heaters, and you energize the O wire to make it switch to cooling. The B type heat pump are cooling by default and energize the B wire to make them switch  to heating.  80% of all heat pumps sold are Type O, and that is the default type on the nest thermostat.  
the last wire is the C terminal. This is for the 24 V AC COMMON power. If it helps you to understand and you know a little bit about AC power you know there’s LINE voltage and then there’s the NEUTRAL. The R is line and C is the neutral. we call it common because the common wire is routed to all the devices and it’s connected to every device in the HVAC system. So therefore, the neutral is common to all motors, blower fans and compressor controllers.  The R is the LINE voltage. 

I hope that this helps you understand if you have any more specific questions go ahead and ask.

AC Cooling Wizard

[Patrick_Caezza]

@JustGarth 

The black wire (W1/E) goes to the * terminal on the Nest and you will set it as emergency heat.