[johnmyster]

My windows are tinted, and yes it helps. FWIW, I have a '98 Sonoma, 4 cyl, manual, extended cab. Approx 31 mpg on the highway, but only with the windows down, no AC. AC drops to around 27. Soon to come are an electric fan and underdrive pullies, we'll see if that helps any. Based on my driving, I could probably drop to 3.73 gears from 4.10s as well.

I'm not worried about the electrical load posed by my blower fan. Ususally with max ac the lower two speeds (of four) are enough to keep me cool on long road trips. I am more concerned about compressor drag on the motor. On those same trips, the floor pan gets really warm. There's got to be 50 sf of floorpan on my truck, and at that temperature, you're picking up a lot of heat through it. Easily 300 to 500 watts or more. Even my shift lever gets pretty warm from the tranny. AC has to overcome all this. Then, as your AC is working, a lot of the cooled air ends up flowing out the doors rather than being contained. If these issues could be addressed, you could easily get by with a much smaller AC system - with a smaller compressor that would pose less load on the engine. Even with the same system, your compressor would cycle more often, putting less drag on the motor if it didn't have to work as hard to keep the evaporator coil cold.

Exhaust wrap and heat shields under the floorpan? Additional layers of carpet, rubber matting, and padding? Sealing off your doors with significant levels of duct tape under the door panels? Installing a valve under the hood to bypass the flow of coolant into the heater core? Perhaps these are the latest ecomods for those of us who occasionally require AC.