I’ve noticed my gas is consumed twice as fast with during hot days when I use my air conditioning (always as low). I know air conditioning will consume some additional gas - but I can almost see the gas gauge lowering when I turn on my a/c. Any ideas on what might be causing this? Should I bring my car for a tune-up? Thanks for any tips for this non-car guy.
it LITERALLY doubles your gas consumption? That’s very extreme if true, unless you put a home central air conditioner on top of your car 
Could be the AC is having to work herder than it should. Might wanna have it checked.
Well I can tell you this, if you’re going to run the A/C, run it high. It will use as much gas with the blower on low as it will on high.
I don’t see your A/C causing enough of a fuel consumption problem that you would actually notice the gauge dropping.
It’s possible that the extra electrical load being applied when the A/C is turned on could be causing a slight voltage drop somewhere in the electrical system.
This would affect the gas gauge reading since it relies on a steady voltage being applied.
The needle movement is then controlled by the varying resistance of the fuel tank sending unit.
We get a lot of these type posts. Someone is convinced his car is getting sharply reduced fuel economy. His reason for such a belief is the needle moving between the divisions on the car’s fuel gauge.
Sorry, pal. Collect some real data. You’ll discover the truth, which I’m convinced is that by using A/C your fuel economy suffers by no more than 1-2 mpg.
Also don’t forget that the hotter the weather (and hotter the gas in your tank), the more the gas expands. It thus has a lower energy density per volume and gets consumed faster to deliver the same amount of useful work. You’ll see the gas level drop faster than you would in cooler weather.
Do you have any mpg figures to confirm the higher rate of consumption, or is this just a guess?
AC should only lower fuel mileage SLIGHTLY, it should not cut it in half, and running the AC on high, medium, or low makes no difference at all. The AC compressor cycles on and off as needed to maintain the correct pressure within the system, and it will do so regardless of the temperature you select or the fan speed.
How did you measure it and exactly what were the results?
I suspect your way behind in car maintenance, and need a tune-up, bad. A car out of tune can easily be using too much gas.
I remember this viral video my mother sent me about using acetone to improve gas mileage. The guy claimed that adding 10 oz of acetone to gasoline nearly doubled his gas mileage. But, if you watch from the beginning, his car, looked like a Toyota Corolla, started out at 17 mpg, and ended at 34 mpg. Well, just catching up on his car maintenance, like the tune-up and tire pressure checks, then adding the acetone, which cleaned the crud off the fuel injectors, simply returned his car to good running condition with the mileage he should have been getting from the start, according the the EPA. A bunch of hooey.