The low side is the one on the driver's side of the car. You need to loosen the STB to get access to it.
If you are seeing 90 PSI in that side, something is wrong. My GUESS is that air is in the system (from the hole), and it's trying to compress the air, which is really bad. That my only guess why you are seeing that much pressure on the low side.
You need to find the leak first. Get some flourescent dye, and add it to the system. How? I honestly don't know. Do some research on the web.
It will take more then 1 can, if empty before, to get the system to cycle on/off.
If you are filling the freon on the high side, stop right now. I hope you didn't break anything.
All systems imploy a pressure switch. This prevents the compressor from coming on when there is no refridgerant present. Do not bypass this switch unless you are 100% sure the system has the correct amount of refridgerant. The compressor will blow, without a doubt.
Scott