High and low pressure switch in air-cond

[monkey spanners]

Looks like R S T go to the phases and A B C are for the control circuit to turn the compressor contactor off in the event of a fault with the supply.
Not sure if A B C are live in and out and a alarm contact or live in and out and a neutral like the kirwan phase protectors as your diagram is not clear.
Just trace the wires on the diagram and see where they go. Or phone the manufacturers tech dept.

[install monkey]

its a common ,no,nc contact-stick 415v on and test continuity on a to b or c to work out ur control circuit,also disconnect the 415v to prove the contact breaks also-carefully and safely

[huntersouls]

Does it mean i need give external power to it on the common pin?

its a common ,no,nc contact-stick 415v on and test continuity on a to b or c to work out ur control circuit,also disconnect the 415v to prove the contact breaks also-carefully and safely

[install monkey]

your low voltage control circuit will loop through the normally closed contact(when 415v is present to the relay

Does it mean i need give external power to it on the common pin?