A/C Triary Switch Question

[AusTx68]

I understand the triary switch serves to protect the compressor from operating outside the ideal pressure range (either too low or too high). It also operates the fan to keep air moving across the condenser. That being the case, if a system is fully evacuated how would it ever charge? The negative pressure in the system should cause the triary switch to open which kills power to the compressor. Right? Is this feature somehow bypassed?

This is purely an information question and not something I'm attempting on my own. I asked myself this question after installing my Vintage Air system. I plan to have it professionally charged next week.