Is there a way I can inject dye into the A/C system without the compressor running?

I'm working on A/C in the car listed above with a 305. as soon as I turn off my vacuum pump , the gauge drops from -20 almost instantly to zero. So I'm assuming there's a large leak.

Is there a way I can inject dye without the compressor running ??

Or do I need to jump the pressure switch , or the compressor , to make it run and accept and distribute the dye?

Should I maybe change all the o-rings first? (all the connections are all under the hood and easy to reach) and then try to vacuum it down again to see if it holds.

Thanks in advance.