My old thermostat has a red wire to R terminal with a jumper to Rc.

[rgaila]

Disclaimer: This thread was migrated from our previous version of the Google Nest Community. You can continue to receive updates on your thread issue here or simply ask, browse or more in the new Google Nest Community.

Original Poster: Celeste Lange 

I'm wondering if the configuration I noted above is compatible with the Nest Thermostat.  It seems it would be according to what I'm reading in the installation guide, but when we finally got the thing installed we started with the thermostat on cool (ambient temp inside was 79 so we set the temp at 70) and the furnace started blasting hot air!  Totally unexpected, but am concerned the thermostat is not able to both heat and cool using only one Red wire to power both.  Any Ideas?

[rgaila]

Hi Celeste, 

Thanks for reaching out to us and welcome to our community! I totally get the confusion behind thermostat configurations, and you never want to be too careful with installation. I'm happy to look into this for you. 

Firstly, out of safety concerns, I should advise that our thermostats should not be be connected to any jumper wires due to their design of one wire per terminal. 

Some HVAC systems, called dual transformer systems, use separate power sources for heating and cooling (Rc and Rh). Since it appears that you have both an Rh and an Rc wire, you might have a dual transformer system. We'd strongly recommended that you contact a local pro to prevent damage to your system.

I hope this helps! Let me know how it goes and if you have any further questions for us. 

-From Ai, Community Specialist.