No point in changing or testing the low/high pressure switch just yet.
Do you know how long the car has ran without a/c not working?
Has the filter dryer ever been changed?
If i was to look at it this is what i would do in order..
Recover gas left in system,
Fill with nitrogen and check for leaks (even tho it sounds like you dont have any)
Then change the dryer filter and vac down for a minimum of an hour,
Refill with refrigerant and check system... Once at this stage if its still not working i would the Go on to check wiring faults and pressure switches
Biggest failure i find to do with a/c is no one ever seems to change the dryer filter! This shoud be done at least every 2 years to keep the system from sludging