Air conditioner gets lukewarm

In the morning or night the A/C is consistently cold. Enough to make you uncomfortable. However, once the sun hits the dash and the outside temperature is 75 degrees or higher, the air becomes lukewarm at best. The A/C was recently checked as a part of a service and emptied/recharged. There are no leaks, the system components seem to be functioning normally, it only happens when it is hot outside. I replaced the blend door actuator under the glove box as it was creaking but the problem remains. With summer here again I cannot go through an Alabama summer with no A/C nor can I afford endless diagnostics from a car shop. Has anyone ever heard of this before?