nest wiring for an old 2 wire system

[joeimel]

My old thermostat is the 2 wire bell wire, no jumpers just the old dial to temp with the mercury vial. is the nest compatible? I cand find a wiring diagram for it.

[CoolingWizard]

@joeimel , you were describing a simple two wire system, which is most likely for a heating system probably gas heat. What does two wires do is simply connect. One wire to the other to initiate the gas heat cycle. This can be compatible with a nest, but there’s gonna be some effort put in to get some power for the nest. Right now those two wires go to the gas valve and connect T to T. This operates at about 600 mW of power and that’s not enough for the Nest. You can make this work with a basic nest thermostat that uses AA batteries to operate. You would simply connect one wire to the RH and the other wire to the W.

AC Cooling Wizard