My car Ac works fine when I start the car. It blows cold air. But once I stop on red light and start driving it start blowing hot air.
Welcome to the forum…
Your best bet is to take it to a shop that does AC work… You need to know what the low side and high side pressures are, and go from there…
Ask your shop to take a look at the the AC compressor; maybe there’s something obviously wrong, like it isn’t spinning at times it should be. Also try turning off any optional electrical loads. Some car designs prevent the A/C compressor from running if the electrical system is over-stressed. A faulty 12 volts car battery btw can overstress the electrical system.