topic nest learning thermostat one red wire "R" - how to wire with Rc and RH---- in Nest Thermostats

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

Peter001 — Sat, 28 May 2022 19:46:53 GMT

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

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

CoolingWizard — Sat, 28 May 2022 22:59:15 GMT

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.

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

Patrick_Caezza — Sun, 29 May 2022 04:30:05 GMT

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.