Help to identify wiring in old thermostat
We just bought a house.
This house has a fairly old dual fuel heating/cooling system (york heat pump and oil furnace) with a york thermostat using mercury.
I attached the picture of the thermostat without the cover.
I'd like to change it for a Nest learning thermostat and sent the picture to Nest support.
From the picture I have attached, they are unable to determine if your system is compatible.
I need to remove the thermostat from the wall to expose the wire terminals. I really don't want to do this since I don't want to break anything.
Is there somebody on this forum that could give me some info regarding my thermostat; serial number, serie or even better wiring schematics ?
Thanks a lot in advance