Ford uses CCOT systems, I think -- that is, cycling clutch orifice tube. You should have a large accumulator up by the firewall, with a large suction hose (the cold one) going to the compressor.
Did you evacuate the system and verify no leaks? If not, you probably have water frost forming around the outlet of the orifice tube, and no freon flow. When the pressure drops, the switch on the accumulator shuts the compressor off (this is the freeze protection system).
Does the engine really load down when you switch the AC on? This could mean the orifice tube is clogged (I can tell stories about a certain Volvo....).
Tell me more, I may be able to help, although I would never claim to be an AC expert!
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!