That is not your low side port. The green cap is indicating the EVAP system and it looks like there is a tag on there as well that states this. That is for your emissions system.
So here are some guides that will help locate the low side port:
https://youtu.be/ON2dYcmXIAw
https://www.2carpros.com/articles/re-charge-an-air-conditioner-system
Below is a chart that will help with pressure readings once we get this and the other is a location on the lines where these ports should be.
Take a look at this and let us know if you have questions and then what your pressures are with the engine off and then with the engine on and A/C on.
Thanks
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Saturday, June 12th, 2021 AT 6:20 PM