Air conditioning problem
 

I have a 2014 Lexus ES 350 with 25,000 miles. Recently, I began having problems with my air conditioning whereby it intermittently shuts down. It seems to occur more frequently on hot, sunny days. I've brought to the dealer 3 times, and each time I get to the dealer, it's working again, and the dealer can't identify the problem. Any advice would be appreciated.