Morning, Brian,
What Hawk said. My limited experience tells me this: Since our West TX area has started to heat into the 90's, my mileage has noticeably increased. I don't go hot - I use the A/C. I don't cycle; I stay comfortable.

My Accord's performance in the heat, with the A/C, surpasses lower temps without it. Several on this board have mentioned how much better mileage they get in warm temps. Sure, the A/C drains *some* FE, but it's more than off set by increases in FE that warm weather bring. At least, in the case of my Accord Hybrid.

'05 Accord Hybrid
'05 Odyssey EX-L
'03 1800 Goldwing
'98 Civic EX (16 yr. old daughter's)