So...does using the A/C affect my mileage?

See post #17. This applies to stop and go traffic as well. The AC will drain the battery rather quickly and cause the engine to replace the lost energy. Once the battery SOC drops into the mid 50s or lower, your mpg will drop until the SOC is back over 59%.

 

if you start a fresh tank with a low average, it is difficult to bring it up.

 

If AC hurts MPG, I guess we can safely conclude White Prii get the best MPG?

 

Only if driven during the day

 

The first thing to do is always to check the tire pressures. That's the most common thing that has a big effect on MPGs. Once a month is good.

 

what i don't get is how many people driving with a/c setting at 70 or higher during the summer??? until my car fully cools down (and even then) the LO setting (64 degrees) just isn't cool enough for me

 

I disagree. It's kind of like when you're trying to get good acceleration up a steep hill. There comes a point where you can jam the pedal to the floor: the engine will make lots of noise and complaining to entertain you, but you won't really make more headway.

Using A/C in a car that's been sitting in hot sun, I'll typically:

1. Start with the system off, windows down, for at least a few blocks.

2. Run the windows up and turn the A/C on and on Auto. Set the temperature fairly high, at a point that the fan speed does not race to full speed, stays in the middle of the range. Typically this is around 26 centigrade (79 fahrenheit).

3. When the fan speed starts to drop, lower the temp, just to the point that the fan speed starts to race again, then back off a half degree or so.

4. Settle on a "comfortable" speed: 24C (75F) is often fine. 23.5C or 23.0C (74F~73F) will get it quite cool.

This all takes a while to stabilize. For short trips, I don't use it, it's too distracting working on it: I'll just leave the windows down.

 

that might work when its 80 outside...but what about when its 95? 79 degrees isn't cooling crap!

 

I think the principal is still sound, regardless of ambient temperature.

Google this:

MSantos Let the hot air out first and then use your air conditioning wisely

 

Here is another plus for the electric ac. I live in very hilly terrain.(sw va) I can run off electric when going down long grades. Then hit the off switch on ac going up grade and find that the car stays cool enough until I can Glide again or find another down grade . It works for me but I do have to turn on and off the ac. Am I damaging anything by doing this ? I don't know.

 

I agree. It's all relative. I don't use my AC until temps are over 100. Otherwise I just crack the drivers window and the rear passenger window and there is enough airflow to keep things relatively cool. That is if someone considers 80deg cool when it's 105deg outside. lol

 

I'd also like to remind everyone that all cars take a hit in MPG with the AC on. Guys on the TDI forums take a huge hit with the AC on in hot weather. Some are losing 5-10mpg.

 

I have found quite a variance in AC fuel economy on my '07 Prius. On the highway, the difference is minimal, however, I live in an area with very twisty, hilly roads, and many of my trips are in the 5 mile or less range. I can swing 43-44 MPG without the AC, but it quickly drops into the high 30s, and I keep the AC between 68 and LO most of the time. I start sweating profusely at anything over 70 degrees, so I have to deal with the MPG hit.

 

Left LA at 6am to Livermore California. Turn air conditioner at the Grapevine near Bakersfield...just normal mode...speed 70's to 80's.....43.8mpg...back trip left very early morning so I5 was cool. Use air conditioner after Grapevine. Normal mode...speed in the 70's .....48.2.....very happy....normal tire pressure...no pulse....just driving.....very happy with results.....wind noise, cancel it with Radio.....

 

Also consider turning off the AC when you are traveling downhill. The engine is less likely to shut off when going downhill with the AC on. This can mean the difference between getting 150 mpg for that segment and getting infinite mpg. I observed this today while traveling downhill from 1300 ft. to 200 ft. over a span of about 14 miles. With the AC off I can shut the engine down and glide for long periods but with the AC on the engine refuses to shut down and let me glide.

You may get the engine to shut down if you simply lift off the throttle completely but now you are regen braking and cutting down on the distance travel using zero fuel.

 

8-13-11
Please refer to the thread, "Why the drop in fuel efficiency?", for a highway test in 100+ Texas heat yesterday with and without AC on.

archiveman2977

 

On my '08 Prius I notice around a 5 mpg difference from not running the AC to running it on medium or a higher speed.

 

I've observed with my gen 2, that A/C (climate control) set higher than the outside temp will tend to keep the engine running at stops and during glides under 40mph to keep producing heat, which significantly affects fuel economy. Once I learned this, I started only turning on climate control while cruising on the highway (when the engine is always on anyway). For my 24 mile, mostly freeway commute, this bumped MPG up from 44 to 46.2.

Only tangentially related, but I recently discovered that my radiator fans had been disconnected for as long as I'd owned the car. Never had an overheating issue (Minnesota), but it does explain why the air conditioning wouldn't work unless the car was moving (the fans cool the AC condenser as well as the radiator).

 

Ouch.

 

Yep.