Y/Y2 terminal on old thermostat.

[ewingman]

I am installing a NEST Learning Thermostat 3rd Gen. I have a Carrier Heap Pump, model 25HPB642A300.  The documentation indicates it is a single stage unit.  The old thermostat has a Y/Y2 terminal.  I did not see any documentation on this for the Nest.  There was an old thread, but they never stated the solution. Do I connect this wire to the Y1 terminal on the NEST?  I assume the Y2 was there in case you had a two stage unit, but I want to be sure.  Thanks.

[David_K · Accepted solution]

The Y2 wire controls a second stage of cooling, so if you only have a single stage unit, connect that wire to Y or Y1 in Nest Thermostat.

[ewingman]

Thanks!