yboy82 3/22/2011If it is above your receiver drier, i think it is your low pressure switch. Try to check out this link
and this link to see an image of a low pressure switch.
yboy82 3/22/2011Before you do anything check out the TSB's and Recalls for your vehicle on this link http://www.automd.com/recall-tsb/search/ just click the title of the TSB or Recall to see its summary or content like the one below
2002 Ford Taurus Equipment Service Bulletin 171137
NHTSA: Action Number: 10008596 Service Bulletin Number: 171137
Sep 01, 2002Component:
Summary: Lack of a/c cooling. *mj