When the compressor engages you have 100psi on the low and 30 on the high? There is no way your system has enough freon for 1 and if the compressor is engaging its not doing it long enough to create pressure. When it engages it should engage and low side should drop low and high side be about 3 times that. You sound about 3 cans low, freon in a system that hasnt been used in a while will just leak out of weak seals on the compressor front usually as no oil is lubricating it. Also you can not properly fill the system with out the sytem on full high cool and compressor fully engaging as you putting in freon. One done at idle you must have someone slowly hit the accelerator to 2k rpms while adding freon to get 35 low side about at 2k rpms. When you shut the car off at your ambient temp the low side should be pegged on your gage.

I hope this helps.