My existing Nest learning thermostat, 3rd gen, is draining the battery really fast when use the wifi. I have a ClimateMaster Water Source Heat Pump. It has only four wires. I run an extra wire to use as C-wire, as I could not find common wiring in the CXM controller. Now I need to connect the c-wire to the blue common wire coming of the 24 Volt side of the transformer.
I would love someone to triple check the way to tap into the common wire:
I can use an adapter to piggyback the blue wire located just above the yellow wire at the board and from there connect it to the C terminal - and the other side would be connected to the nest thermostat.
I am attaching some photos with the existing wiring.