Basic air conditioning wiring question

[oldfox]

Hi I have a question about air conditioning wiring
I know that 12 volts comes from the switch in the dash and then runs through the pressure switch that shuts off the compressor if the 134a gets low then to the relay that sends the 12 volts to the compressor.

But somethings missing here,, Isn't there a switch something like a thermostat in the evaporator core somewhere to shut the compressor off if it gets to cold to keep it from freezing up?

Is it tied in on the negative side of the compressor magnet?
or does that run straight to a ground?

and How does it kick off and on when it's at an idle?

I wish I could draw a schematic on here.

[oldfox]

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