2001 Nissan altima ac cherps like a belt squeak and comes on but doesn't work all the time it is fully charge

Chirp probably is belt. But the A/C system uses a thermistor inside the evaporator case (nissan calls it a A/C amp) That is what l would just plug in and see if the A/C starts and cools. Located behind the glove box. Then take time to seperate the A/C case and reach in with long needle nose pliers and pull the old temp probe and install the new one approxmately the same place push the red end into the cooling fins.