Pentair swg ic 40 red flow light

My pool is 2 years old. I have a salt water system with a pentair ic 40. The red flow light is on. I have taken the unit off and cleaned with acid cleaner from pool store. There are no obstructions as far as I can tell. I called Pentair and was told it might be the flow switch. How will I know? I was told I could disconnect plumbing and turn on electrical and touch the switch to the plastic piece. However, if this doesn't turn the light green there still remains 2 options: it's still either the switch or it could still be the swg. Is there a way to determine before I spent $100 on the switch to find out it is still the swg? Thanks for the help.