mighty max a/c

ok here we go just got a 1995 mighty max today and the a/c compressor would turn on and then off so i check the pressure and i was 100psi so i got all the pressure out of the line and put more in around 35psi and the compressor stays on but it still was blowing hot air and i checked pressure and i was at 70psi in about 5min and still rising so i turn the a/c off and not sure what to do next to me i seems like there something stopped up and the ac compressor is building up pressure. any help would be greatly apperciated thanks

sounds like a bad expansion valve