Air Conditioning and MPG

battery efficiency, better in warm temps, less rolling resistance in warm weather, less use of the heater which takes the ICE coolant temp down quicker resulting in more ICE operation, and the psychological effect of cold weather, which results in the " I gotta get there quicker to get out of this cold air", nothing like cruising along with the window down enjoying a warm breeze.

 

They had a great segment on Mythbusters recently, comparing milage using an SUV with air con running, vs one with the windows rolled down.

In the end, the windows-down SUV managed 15 laps (7.5 miles) more than the AC SUV.

Of course, our Priuses use a different AC system as has been mentioned here, but it would be interesting to do the same test to find out what the difference is on a Prius.

Not that I really care mind you, if it means comfy driving instead of being hot and cranky, I'll happily lose a few MPG. My 04 handled the 39c (102f) temps in northern California in the summer without any problems whatsoever. Of course, it felt like stepping into a blast furnace from the 23c (73f) temps inside the car.

Dave.

 

I think if you compare, say, 100 degrees to 70 degrees, you'll get better mpg at 70, when neither heat nor A/C is on.

However, if you compare 20 degrees to 100 degrees, you'll do better at 100, because running the heater forces the engine to run a lot more. And at 20 below zero, the battery becomes inefficient and the engine almost never shuts off.

In the Corolla, the engine has to run all the time anyway, so the cabin heat is free. In the Prius, in warm weather, the engine shuts off a lot, providing tremendous gains in efficiency. But in cold weather, a good part of that efficiency is lost, therefore mpg drops significantly.

The Prius still gets better mpg than the Corolla at cold temperatures, but the difference is a lot less than it is in warm weather.

So to summarize: both hot and cold weather take a bite out of Prius mpg, but cold weather takes a bigger bite. Cold weather does not take as much of a bite out of the Corolla's mpg, because it's always burning too much gas anyway.

 

Also, 04/05 prius has a variable speed compressor and continuously variable cabin fan. Once the cabin has cooled down, the most efficient speed of fan and compressor is used to maintain that temp.

In a corolla, you regulate the cabin temp by either fan speed, or adding heat from the heater core, the latter being grossly inefficient.

 

In 82 degree outdoor temperature, I was on highway at 55 mph. I reset the average mpg, turned on a/c and I averaged 48.7 mpg for 10 miles. I turned off the a/c, reset the average mpg, and averaged 45.5 mpg. With the a/c off, I observed the electric motor kicking on,momentarily, about every 1-2 minutes. With the a/c on, the electric (engine that propels car) only kicked on (to help the gas engine) twice during the 10 miles. I believe the electric will kick on at high speeds so the battery doesn't over charge. One would think that the voltage regulator would do this. The engine charges my battery much faster with the a/c off. The only thing I can thing of that engaging the electric engine momentarily puts drag on the car, reducing mpg. I need more information, but as of now, I plan on running a/c on 90 degrees in the winter. Any information on this and /or the voltage regulator would be great appreciated.

 

I think you should post in the Gen III forum, this is for Gen II and will be different in some details.

 

I forgot to include that I could feel the car slow, while the electric motor kicked on. In my humble opinion, the above comments are correct, but it doesn't explain why my mileage increased with a/c on in same ambient temperature. Please help.

 

Don't want to sound rude, but you are driving a Gen III and you should ask these sort of things in the Gen III section of the forum.

I can't help you since I am not familiar with the Gen III. I do know they are different than the Gen II I drive.

You should get more and better response if you post in the Gen III section.

Best of luck to you and welcome to Prius Chat.

 

9 year old post!

 

Likely brought up by the new member.