My ac is an old lennox, it's high pressure sidestarts normal 150 ish but continues to rise to 500 before the pressure release valve opens. Low side pressure starts around 60 and climbs until 85. Outside air is 90 F, vapour line is 80 F.
I'm thinking there's a blockage what do you think?

Have you? Before you can get a good correct reading you need to make sure everything is clear and clean.cleaning of both the condenser and evaporater coils,filter and all vents open supply and return
Then get another reading
Let us know what you come up with

Condenser is clean, registers open but not sure about the evaperator coil it is an uncased coil so no easy access. Filter was clean.
Ken