AC Won't cool

I always do. I think you can put the first one or two cans in upside down, I’ve done it on cars and Trucks. I don’t anymore. Always heard of risking blowing up the compressor putting it in Liquid form (upside down) vs. gas form ( right side up). A couple years back, my air wasn’t keeping up, thought it was low. Decided to throw a can in it. I was in a hurry, turned the can upside down, and split my Sanden compressor wide open. Turned out, my system wasn’t low, but the high pressure switch wasn’t working. High pressure combined with the refrigerant added in liquid form to an already full system actually split a perfectly fine one yr old compressor body wide open. Made a believer out of me. Sometimes my Truck takes 45 min. or more to get the last can or two in. I’ve often run down the road with the last can hooked up. I’ve been told putting the can in warm water speeds up the process.