Air con compressor wire

just a quick Q to yooz that know about air con systems - my compressor has a wire attached to it that goes to a realay - is this an output to show when the compressor is running? or a control wire to enable a clutch or summat?
unfortunately I have 2 types of relays - "A" and "B" types - and I am not sure which to fit as replacement.

It is usual that this wire goes in just behind the clutch mechanism to engage the clutch , some have another set of wires that will go to a sensor/switch but is rather a rare set up, usually that switch/sensor is on the drier, or expansion valve .
The clutch wire goes thru a relay , that is controlled depending on fan being switched on , not o/heat or o pressure or no pressure and thermostat , so unless you are using as a tire pump you cant just fit a relay and switch on compressor HTSH

Thancs Taco - I will Pm yu the circuit (as far as I can make it out) for your perusal, if that is OK? and any ideas. It is a bespoke system - so I am reverse engineering it.