Just bought a new apt in Spain and would like to hook up a NEST Thermostat

[MariaKors]

I have 3 wires Red Black and white. it looks like no C wire. The unit was built in 2022 and the air conditioning system is a GENERAL. Can I install a NEST thermostat.

[Brentg]

you need an additional 24V source wire to constantly power the nest battery which requires to be terminated onto the common terminal point on your wiring harness 

[MariaKors]

Thank you,  the unit  is a General ACG 45 UiA-LM unit. How and where do I connect the 24 V source wire from and to?? When you say wiring harness what does that mean? Sorry first time doing this and this is the best answer I have received,  I have been asking here in Spain for about a year!! They are not very familiar with the products and in the USA I was able to take the old thermostat off and easily connect the new one. 

I will hire an electrician but I am sure I will need to accurately explain it.

Maria 

[Brentg]

Did you get this hooked up yet? Or are you still having trouble?