I'm sorry to be blunt, but if you're asking this question, DON'T DO THIS WORK. Leave it to professionals with licenses to handle refrigerants, check system pressures, and check for proper system electrical operation as well.
RepairPal Certified shops can diagnose and repair your 2005 Ford Thunderbird. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.