alan perrins

hi all, new to Jag and new to this forum... Hi!!! problem with my air con, seems to work ok at speed but not under say 30MPH. ive been told its the DPS valve on f/book forum, but garage says they cant locate part and want me to buy complete new unit!! model is a 2011 mk1 3.0d portfolio any help gratefully received, thanks in advance BTW, thought this would be a common problem and have searched past topics but found nothing?