2002 yukon ac blows hott but cant find any leaks

Hi, i have a 2002 yukon and all of a sudden the ac started blowing hot. We put freon in it and it stays cool for a day then it blows hot again. We had it checked for leaks but they can not find any leaks. ac mechanic is telling me that it can be something that is in the rear of the vehicle causing it to continue to blow hot he also told me where the problem might be coming from i have to remove the seats in order to get to it. if anyone knows anything about this please reply!!!!

What does the 134a guages read?

How do i read that?

Sounds to me to be more of a selector door problem, like the door is not moving from heater to A/C mode. Sounds like you need another mechanic too.

Temperature mode door or cooling fan clutch. Been seeing lots of both this summer. Gauges would help verify the fan clutch. High side pressure will be well above 300 psi, maybe even 400 psi. Is the compressor running when it starts blowing hot? Have had cycling switch problems too. It's out on accumulator. If you tap it and the compressor come on, bingo. Easy fix