Pressure too high on fridge vacuum side.?

I have a Frigidaire that i got for free new because it didn't work. I found out it had a hole in the condenser unit so I replaced it & added a new dryer filter. I found the spec for the amount of freon from inside the fridge 5lbs. I charged the system slowly with the can right side up never staying between 0 -5 psi. and used a digital scale to tell me when i've added enouth freon. I let the unit sit for hours so it can start to cool down. The PSI stays at about 0psi....It never cools. after about 8 hours the pressure jumps up to 50psi & the compressor stops coming on. What is wrong with this thing?