High side high and low side high indicates :Expansion valve stuck open,
excessive moisture or air in system. Hope you kept the vacum pump on for
many hours. Using r-12, you probably are using the old CCD expansion valve
(origional equipment).I have never found one that still works(I am sure
there are some out there).I think you may need a new valve.If you spray
liquid freon on the head  of the valve , it should fluctuate pressure on
your gages.You can also put the sensor bulb in ice and water solution .Got
to start it up to do this. 250psi will not bust the system .I dont think
you have enough r-12  in the system to have liquid refrigernat going back
to the compressor.The compressor ,compresses.Thats all. When it goes bad,
it usually compresses less-- given that everything else is ok.Why new
hoses? Also make sure the condenser fan is coming on.Check the fuses to the
right of the 12 fuse pannel.Also make sure you are using the proper scale
on the gages.