air test

Hello to all-auto trans noob here with a question. I am in the process of rebuilding my first trans (C6 from a 1977 F250) and have arrived a the point of reassebling and air testing.

When I apply air pressure to test the reverse/low piston and the forward clutch piston I get no response. Is there anything in particular that I should be looking for? How much air pressure does it require to perform this test?

I need to finish this project soon but I don't want to put it back in the truck unless I am confident that it will perform as expected.

Thanks for any help/info you can provide.

Gene