Lmao, I'm sorry. I can't help but smile and shake my head at your situation! Not because I think it's dumb or anything, but because I completely understand. I live in AZ, where today, it was 101 degrees at it's hottest. And it's supposed to be fall. Pff! Funny -.-
But I relate with your masturbation-situation . When it's hot, I am not in the mood to do anything. Not just sexually, but in general. It just puts me in a terrible mood. My ex gf hated it when I'd say no to sex because it was too hot. She didn't feel the same, or even seem to understand my disinterest in getting it on in an freaking oven. But she was a nympho in the worst sense of the word, we won't go into that ^_^
SOLUTION! Get a towel, soak it in cool water, ring it out (or don't, your choice), and then lay it on top of you. Or cuddle it. Or move it all over your body while you do your thing. Whatever works for you! Have fun