We'll skip the lecture on the accuracy regarding these types of fillers, I've never used them, see the stickies.
We'll assume a working system with no refrigerant, leaks fixed
When you connect the hose to the LP port (on the accumulator), squeezing the trigger will allow can pressure to read on the gauge, this will be high depending on the temp. What should happen next is the compressor will kick on, it will make a burbling sound. The compressor will draw some refrigerant out of the can, lower the pressure and kick off. The pressure will build up and the cycle will repeat. The 94 vehicle refrigerant capacity is 2.25 lb.
If the compressor does not kick on, the pressure switch may be bad. This is the switch with the wires coming out of it below the LP port. Remove the connector and jumper with a paper clip. The compressor should come. Do not exceed three seconds. Running the compressor without refrigerant and the oil it contains will damage it.
If the compressor still does not come on, most likely problem is a bad compressor clutch. Wiring problems are also possible.
The fittings are known for minor leaks, this is the reason the caps must be kept on when not in use.
Standard caution applies when working around moving parts and wear goggles.
Hope this helps. Ask questions if not clear
