99 mercury villager- freon

When the Low pressure is 25-40 psi and High at 200-225 psi

In an ideal world and car condition, the pressures would tell you everything but there are dozens of things that will change pressure readings, especially with cars that have 2 speed fans and there is actually no accurate way to know a system is full except to completely drain it, evacuate the system of all air and charge it with the exact specified weight of refrigerant.