You need to disconnect the trinary switch connector down by the dryer and short out the pins for the low and high pressure. I only have wiring diagrams for a 97 so I don't know which of the pins are what... but if you get it right the compressor will come on regardless.
Another option is to "hot wire" the compressor clutch, it's a single wire that you put 12 volts on.
But the real question is why do you need to in the first place? The reason there is a low pressure switch is because the compressor is lubricated by refrigerant. If there isn't enough in the system you will likely damage it.