1988 dodge 250 ram

I have a 1988 P/U that I have replaced the ac compressor dryer and evaporator and expansion valve. There is no cooling the high side line gets hot when charged the low side remains at ambient temp. when the compressor kicks in the low side pressure reads about 10 when the compressor cycles off about every 10 seconds the low side pressure rises to abbout 70. whats going on?