Opeerating A/C

[lenientism]

On the top picture The on/off switch of AC (center bottom left) did not work when bought. The seller said I can operate AC without having to push the switch on and off, alternatively just switch the fan (left) and thermostat (right) switch to the desired level.

Having tried to fix the (AC) switch and succeeded it works again indicated by engine RPM is moving. Sorry for my ignorance, what this switch actually works for?

[PJ S]

Not 100% sure I understand the question fully, but if I have, then the AC switch is what kicks the compressor into life, the setting of the thermostat without the AC switch engaged only has the fans blowing over non-heated elements, so the temperature in the cabin will never be as cold as with a fully functioning AC engaged.
So, imo, the seller was incorrect in saying the AC will still be active with the thermostat set all the way to the left - that's just cool air, not cold and dried air which the AC provides.

[FWDRacer]

The switch allows the clutch of the A/c compressor to engage/disengage. Without the compressor being operative in the system you have no A/C - No matter wehere the dial (thermostat) is set.

[paintman]

If the pressure in the system is low, even though the compressor might engage you may find no cooling occurs - check the pipes, but be careful as they can be very hot.
If the pressure in the system is very low & the system has a pressure switch the compressor may not engage at all.
Sounds like the seller has pulled a fast one.

[lenientism]

I think so, the on off knob is to activate AC engage and disengage, without it there will be only cool air, not cold and hot air like what does AC work for.

The seller might want me to buy his car immediately. I have driven cars with very simple AC control panel, comprising only two knobs of fan and thermostat controller, no AC on/off knob found.

PJS I think you got the picture of my question correctly. The seller said I can operate AC only using the left and right controller.