I deal with vincents alot, they are a neighbor of mine. Anything weird comes in, I send it to Candy, and let her sort it out. Be careful of doing it yourself if you lack experience. Ive made my fair share of money from people making mistakes. Make sure theres enough oil in the system, etc. Unless a scorcher hot day, high side pressures are goin to run around 250 psi on R12, once it levels out. Low side varies according to evaporator temp, but hot weather liek today, on high speed, youll see 30 psi I bet. If theres not enough air getting thru the condencer, or weak fan clutch or its just hot, you could see 300psi, but thats the highest you better see R12. If you fill it to what the capacity is and pressures are low, chances are you dont have enough oil. Hope this kinda guides you. Good luck!