1997 defender 90 a/c

1997 Defender 90 a/c problem . I replaced the expansion valve one month ago July 2009 . for high pressure gauge readings 90 psi low side 320 psi high side . Vehicle returned to shop with warm air coming from vents . compressor operating , but gauge pressures now showing low side in a
vacuum and high side 170 psi . Help greatly appreciated

rovertec1958