Is your radiator cooling fan running? Sounds to me like there is no heat being extracted from the condenser.......
Edit to add....that is the only thing that makes sense here unless you are grossly overcharged with refrigerant. The evaporator absorbs the heat from the air and the compressor compresses the refrigerant at the condenser to get rid of the heat.....the only way you can get high pressure on the high side is if you have a ton of heat build-up in the high side.....like no air flowing thru the condenser. High side pressure is directly linked to temp. It is impossible to have extremely high high-side pressure without having equally extremely high high-side temperature. If there is a restriction in the low side (plugged orifice or metering valve)....as my AC instructor in tech school used to tell us, "if she can't suck, she can't blow". In other words, if the orifice is plugged and nothing is getting thru, then the compressor has nothing to suck. If it has nothing to suck, it has no way to build pressure......just like if your PS pump has no PS fluid in it, it has no way to suck that fluid out of the reservoir to pump it and build pressure. Everything you describe here fits perfectly with no heat being extracted from the condenser. Once the entire system is "heat soaked" to max capacity (because none of the heat is being extracted from the condenser) it can't cool anymore and goes over-pressure.