You should use a manifold gauge set for this job. On a manifold gauges set, the blue line and quick connect fit the low side and the red line and adapter fit the high side.
In refrigeration 101 you learn that the high side connection is somwhere between the compressor outlet and the expansion device while the low side connection is somewhere between the evaporator and compressor inlet. After the first day of the first class in refrigeration 101 you know that flow goes from compressor to condensor to filter drier to expansion device to evaporator and back to compressor. If the system has an accumulator instead of a filter drier you find it between the evaporator and compressor instead of the filter drier location.
Once you know those basics you can identify low side and high side on ANY system.
You can buy a great manual from www.ackits.com for $19. I would highly recommend that you "bone up" before going very far with this job. Lack of theory knowledge will cause you more problems than you correct.