Ian wrote:
On Saturday, December 14, 2013 10:52:40 AM UTC-5, Ian wrote:
I am installing a new NEST thermostat, replacing an old two wire mercury bulb furnace thermostat. There are only two unmarked wires. There's 24 V across the wires.



Can anyone tell me which letters on the NEST base (W, Y, O/B, AUX, E, G, C, etc) they will map to? It has to be the most basic of installations; open or close the circuit.



Thanks,



Ian

Yes, it comes with installation instructions, and I have read them, but there is no reference to a simple two wire (unmarked) set up.

And, yes, I know the nest has the capability to control much more than I have, but I want the ability to program, and control remotely. It's only marginally more expensive than the basic ones that provide that functionality.

In the end, I believe the answer is to connect the wires to Rh and W1.

Thanks,

Ian

Hi,
Yes, indeed but you have to connect right wire to the corresponding
terminal. W1 means 1 stage heat, RH means 24V AC control power lead, H
meaning for heating. If you cross this wires you may damage the 'stat.
Take a look at the furnace end to see if you can sort out this two
wires. If you measure the voltage between furnace frame and this wire,
one showing 24V AC or so is one for Rh terminal, the other one is for
W1. Some times wires are color coded.