nest learning thermostat one red wire "R" - how to wire with Rc and RH----

[Peter001]

Hello,

changing from old  Carrier thermostat -which controlled heating and cooling

original wire connections are "C"  "G"  "Y1"  "W1-o-b"   and "R"

Nest thermostat is showing RC and RH  which I understand is heating and cooling

Solution?

screwed?

Jumper?

just one will work?

can't find similar posts and it is very hot outside

thanks

peter

[CoolingWizard]

Peter, the Nest will need only the R on Rc.  The others are straight forward until you get to W-O-B.  If you have Gas heat, the wire will go on W on the Nest. However, if you have a heat pump, the wire will go on O/B.  Y is a wire for Cooling.  That is, the Y wire turns on the Compressor.  The G is for the Blower fan, C is common return for the R.

So why the the Rc Nd Rh. When the heating systems are separate systems, they each have a control system powered by its own transformer.  In those cases the separate Rc and Rh are used.  Now, let us talk about heat pumps. A heat pump is the compressor (Y wire) and the O/B wire to energize the 4-way reversing valve. Why two letters. Some heat pump systems default to heat, and some default to cooling.  The Nest thermostat can be programmed for either type.  The O systems are cooling and the O wire energizes the reversing valve and thus it is heating.  If your system is a B model, it starts in heating and the B wire is energized to switch the reversing valve to Cooling.  I hope this helps you. 

[Patrick_Caezza]

Make sure that you connect the wire going to the W1/OB terminal on your original thermostat to the correct terminal on the Nest Thermostat. If you have a conventional system, connect the W1/OB wire to the W1 terminal, but if you have a heat pump system you want to connect it to the OB terminal on the Nest.