Which terminal should I connect it to for a “C” wire on an american standard AM4A0A30

Question

I'm trying to connect a 3rd gen Nest thermostat. I have a 2 zoned heat and 1 zone AC. The zone with this thermostat has a boiler wired Rw, W1 and HVAC wired Rc, G, Y1. It's summer so I'm only using the AC currently, but the thermostat seems to be drawing power from my 2 zone relay attached to my boiler even when the heat isn't on. It keeps triggering it on and off constantly. I called NEST support and they said I need a C wire that needs to come from the HVAC not the boiler.

I'm looking at the wiring for the HVAC and I'm not sure terminal to attach the common wire to.

Any advice would be greatly appreciated. Thanks

Tech · Answer

to answer the question you asked. The "B" terminal is your common. You will definitely need to pull more wires. And YES you need a common for the nest to work. 
 To make your life much simpler, you can add a FAST-STAT Common Maker Thermostat Wire Extender (Adds a Common "C" Connection). hope this helps

Which terminal should I connect it to for a “C” wire on an american standard AM4A0A30

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