How long did it take to lose the refrigerant. It could be only a slow leak and could be easily recharged. You're right if the refrigerant is low, the low pressure switch will prevent the compressor from coming on. Visually check all your connections though, including the wire to the compressor and the relays on the fender well.
By the way, I'm a Grand Prairie High School graduate, class of '67.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in