Toyota Prius Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter · #1 ·
I just got my 2005 Prius a few weeks ago and I love it; however, a few days ago I read in the paper that Prius gas mileage will plummet when max AC in the summer or the defroster in winter is used. Since I live in Phoenix, I am worried! Is this true? Anything I can do to get better mpg? And please don't tell me to not use AC--110-degree weather won't allow that!
 

·
Registered
Joined
·
319 Posts
Winter MPGs did drop here, but I only visited 39 a couple of times. 42 was more common. Temp set for 70 instead of 78 helped. Limited defroster need now that I have a carport. I'm now at my 2004 "nice weather" average of 48MPG since it has stayed warmer.

"Max A/C" may involve having the blower go at top speed all the time, which would only happen if you did it manually or if the car decided you never got to the temperature you wanted in Auto mode. Constant battery drain will make for more recharging later.

Given Phoenix's temperatures, if you set the Auto temp to max (85 I think) and the A/C never throttles back, then just turn off Auto and live with whatever fan setting you find comfortable. Recirculate may help.

If 'comfortable' means fewer MPGs, then that's what you're stuck with...
 

·
Registered
Joined
·
2,348 Posts
johnniemay said:
I just got my 2005 Prius a few weeks ago and I love it; however, a few days ago I read in the paper that Prius gas mileage will plummet when max AC in the summer or the defroster in winter is used. Since I live in Phoenix, I am worried! Is this true? Anything I can do to get better mpg? And please don't tell me to not use AC--110-degree weather won't allow that!
Of course use the AC! Your mileage will go down somewhat, but still double every other car on the road. Turn your thermostat the the warmest comfortable setting and just enjoy the car. "Plummet" is way overstated. Low to mid 40's is still bragging territory!
 

·
Registered
Joined
·
37 Posts
Can't speak about Phoenix, but down here in Tucson, where it's much cooler (~5 deg) during the summer, I have no problem keeping the MPG in the low 50s.

Thanks,
Shawn
 

·
Registered
Joined
·
7,161 Posts
I was wondering, why Max AC? Set to desired temp, and when (or even if) your cabin reaches it, it will throttle back the fan and AC compressor. If it needs to go max AC, it will, but give it a chance to throttle back.

Both the cabin fan and AC compressor are continuously variable, so in Auto mode, it will set the best setting for both to get to your desired temp, then to maintain it. It also monitors the humidity in the cabin, as well as how much solar radiation is reaching the windshield, and adjusts accordingly.

Both the fan and AC compressor are all electric, and of course the electricity has to ultimately be created somewhere. So unless you are perpetually going downhill, some fuel will be used, but still much more efficient than a one speed mechanical AC compressor that tries to chill your cabin as cold as it can, where you have to reduce fan speed or add heat to bring it to a more comfortable temp.
 

·
Premium Member
Joined
·
2,815 Posts
On the Classic Prius, the "Max AC" button causes the air conditioner's pump to run continuously.

In both the Classic and 2004+ Prius, the front windshield defroster uses the air conditioning pump to dehumidify the air.

In the Classic Prius, the AC pump was run by a belt off of the gasoline engine, like on most cars. The AC pump will cycle on and off as needed (fan stays on, but if the temp rises to a certain level the pump turns on again to re-cool the air). However, if you're say stopped at a traffic signal and you need more cooling to reach/maintain your desired temperature, your gasoline engine may come on just to power the AC compressor... So, in hot climates, your MPG will go down in the hot summer with the AC use, as opposed to you not having to use the AC.

In the 2004+ Prius, the AC pump is powered electrically, directly off of the hybrid battery. The AC will still cycle on and off as needed, but the gasoline engine is not required to come on to power the compressor. However, if the hybrid battery's charge gets too low, the gasoline engine will have to come back on to recharge it, so you still will see some lowered MPG in the hot summer with the AC on...

In a traditional vehicle, you don't notice the AC useage hit as much, since your engine is running all the time anyways, you just might notice a lessening of available power with AC usage.
 

·
Registered
Joined
·
884 Posts
Note to "johnniemay":

I saw that article too, and I don't that that reviewer knows much about hybrids. I think the article was probably written after a 10 minute ride and a little surfing on the Internet.

I have a 2002 classic Prius and am getting about 50 mpg city right now, with no AC (because the weather is so nice). In mid-summer, my mileage drops about 3-5 mpg. Despite the high Phoenix temps, I have never used MAX AC. Just set the AC at the highest temp that's comfortable.

In the classic Prius's, if you use RECIRCULATE after the car cools down, the cool air will last through a normal traffic light cycle, without running the ICE. However (though unnecessary for newer Prius's), at really long lights, after I stop I turn the AC off until traffic starts up again to keep the ICE from running.

Dropping to sub-50 mpg in the summer is kind of depressing, but I still laugh at traffic lights when I pull away from those Hummers in Scottsdale, who are accelerating slowly to save fuel now that premium is about $2.35 a gallon. Maybe I'll feel a little more sympathy when gas gets to $3 or $4 per gallon and hybrids are the only cars on the road. No wait, then I can drive on the 101 again!
 
1 - 7 of 7 Posts
Top