Does the A/C reduce mileage?

Anyone who thinks the drop in MPG is significant with the A/C on and is bothered by it, I recommend getting treated for OCD. Get treated before it's too late, please!!!

 

<div class='quotetop'>QUOTE(hyo silver @ Oct 4 2007, 06:50 PM) [snapback]521502[/snapback]</div>

Yes. But windows up, AC off uses even less gas. As said earlier, all the energy ultimately (unless you have a plug in) comes from the gasoline. And it DOES take energy to run the AC if there's a temperature difference between inside and outside.

Dave M.

 

<div class='quotetop'>QUOTE(Bob64 @ Oct 5 2007, 08:06 AM) [snapback]521666[/snapback]</div>

This may be true, but the PHEV folks have also discovered that the battery ECU starts limiting current well before the fan goes to 100%. Part of the calcars PHEV conversion is a mod to the oem battery fan to make it come on stronger sooner, to maximize EV/assist availability.

Also interesting to note that the DOE study found a big hit on the '01 Prii they tested, as I recall about 10mpg with AC on! I believe the '01's used a traditional belt driven compressor didn't they? Seems like the '04+ electrical compressor is a big improvement with regards to efficiency!

<div class='quotetop'>QUOTE(dmckinstry @ Oct 5 2007, 01:12 PM) [snapback]521862[/snapback]</div>

True, but you are ignoring the battery temperature issue. As the battery heats up, the ECU turns down the available charge/discharge current (CCL/CDL) until its basically off. Since the battery uses cabin air for cooling, hot cabin = hot battery. While its true that the AC must consume energy, its also possible for the disabling of the battery to result in a greater loss of efficiency and consequently lower mpg than the AC on condition.

Rob

 

<div class='quotetop'>QUOTE(David Beale @ Oct 5 2007, 11:28 AM) [snapback]521806[/snapback]</div>

Are you talking all four windows open all the way? That would make a big difference. When I put the windows down, I generally have the front drivers' side down 2-3" and the diagonal (back seat, RHS) down about 2". That gets a good cross-breeze flowing thru the whole car, and by keeping the front window down a bit more than the back window you avoid that annoying low-frequency beat. At low speeds (<50mph) this uses less fuel than the A/C, but at high enough speeds even the partially-open windows probably use more energy.

 

I think the A/C drain varies a lot depending on how strong it's running. I did seem to notice a drop when it was 115F here and the A/C was running full power pretty much all the time. Now that it's cooler and it runs less (or not at all), I seem to be getting better mileage.

 

<div class='quotetop'>QUOTE(PriusOwner004 @ Oct 5 2007, 12:58 PM) [snapback]521853[/snapback]</div>

Smiling. That's me! Unfortunately the meds made me sleepy. So I stopped taking them. Now I'm just....well...hot. At least I'm awake while driving now.

 

What I've been able to see since I got my CAN-View is that the biggest draw from using the AC is (a) when it runs on high when you first startup in order to bring the cabin down towards the setpoint and (B) when the engine is off (stealth/EV).

The AC on full-blast is easily 12-15 amps coming out of your battery. That's pretty darn significant, especially when you startup and pull 30-50 amps in stage-1 warmup to get yourself to even 25 MPH.

Advice point #1: Don't run the AC until stage 1 is complete. Open your windows and let the wind take out the really hot air that may have gathered inside while you were parked in the sun. Corollary: park in the shade and crack open a window or two -- it really helps!

Advice point #2: Don't run the AC when your engine is stopped for more than a brief while. Turning off the AC for the 10-45 seconds you're at a stoplight will really help not bring down the SOC of your battery. If you've been running the AC for a while already, it won't get much hotter in your car during that time. This also goes for long stealth glides. At 40 MPH, you're pulling at least 5.5 amps as it is. Don't pull another 10 if you can help it -- just turn off the AC for that 30 seconds. Then turn it on when the engine is running (i.e. while you pulse back up). This may sound a bit ridiculous -- but on a 35 mile mixed city/highway trip that I do pretty often, my highest MPG record was when I had the AC on and used this method!

Once the AC has brought the cabin down to a reasonable level and it cuts back on the amount of power the compressor consumes (a big advantage of the Prius system), thing really aren't that bad. This is why there isn't a huge hit on long distance highway driving, and there is an enormous hit on really short city driving. Once I moved such that I was 3 miles away from work, I stopped using the AC altogether for my commute, because it would bring my trip MPG down at least 20%. I'm not even kidding...

Anyway, the moral of the story: Use the AC judiciously. Having the CAN-View really helped me understand how to use an energy hog more wisely without a big sacrifice .

 

Well stated, and a Prius A/C system only works efficiently with 100% A/C charge, not90% not 110% after that it relay starts to over work, run all the time, and use more AMP's drain down the battery fast. so simple. My work is A/C only all day long, and i can watch the AMP's suck down the battery on a hot day as I remove oz by oz of refrigerant charge out of a Prius. then as i slowly recharge and it cools the cabin faster and once it stabilizes the the cabin TEMP its energy uses drops to minimal. If the A/C system is under or over charged I will see the compressor working hard all the time trying to cool the cabin but it cant so it just keeps on working. Drawing AMP's like our government uses our TAX dollars!!