Air Conditioning...

If "the battery never runs out," then you'd be right. But, that's nowhere near true.

No energy is "free." All energy that goes into the battery came from gasoline at some point. So, if you're discharging the battery to power the A/C compressor, you're still using energy that (originally) came from the burning of gasoline by the ICE. So, therefore, usage of the A/C affects mileage.

 

I understand your point of view, but if you are going down the road at hiway speeds without a/c, you are using the ice and recharging at the same time. If you are doing the same with a/c on, you are using ice and recharging at the same time also. At that constant speed, you will not discharge your battery using the a/c ( at least mine doesn't). So if you are driving without idling enough to kick on the ice, how does that use more energy than driving without the a/c?

 

Not true. Sometimes you will be recharging, sometimes you will be drawing power from the battery, sometimes (though rarely) you will be doing neither. If you are using the A/C you will need to be charging more often, for longer periods of time, or at higher amps. Whichever it is, it means you will be using more fuel to compensate for the additional electricity that the A/C is pulling out of the battery.

One exception to this would be if you are heading down a hill steep enough and long enough that the battery would be charged as full as the vehicle allows before you reach the bottom. In this case, the vehicle will be using friction to dispose of any excess energy as you continue down the hill. Running the A/C just before and during this down hill run would make better use of the excess energy to increase the comfort level in the vehicle without using any additional fuel.

 

One issue not discussed in this thread is the relationship of fan speed. THis last weekend with temperatures here in the 90's - ran an experiment while traveling about 120 miles - first for the first 15 miles - fan was on high - the mpg seemed to stabilize right about 40 mpg. Then set on med. MPG then stabilized about 46. When we went to low - the avg. MPG went to close to 50 MPG. I think that the temp. was set to 72 deg. all the time.

 

Just wanted to piggyback on this thread about A/C, having nothing to do with MPG.
It's been pretty hot and humid here in the low 90's lately and even with the setting at 65 and fan on full blast I can't get the cabin cool. I only have 2k miles on the car. Getting perturbed listening to the fan on high all the time. I'm going to take it in to the dealership tomorrow because I think the system may need some additional coolant or something. Is anyone else having this problem? Advice?

 

Had you left it on AUTO you would have probably been between 46 and 50 from the start. Your logic may be good but it is not as good as the fuzzy logic that the AC ECU uses.

 

If the sun is shinning put your hand on that huge dash. Mine is black and it gets so hot I have to remove it, even with the AC going full blast. I ordered a Dash Cover to help keep it cool

To get this thread back on track see this thread: Looking for HALF of a Dash Cover

I ran some very simple tests while on a trip.

Bob

PS The cover is supposed to be delivered this Friday, the 13th.

 

When it is over 100 degrees as it has been here the last 3 days, Ac will run and I will just have to settle for my 47MPG and stay cool.....I can live with that.

 

rsforkner- Thanks. I'm going to order one as well from Dashtopper. I didn't recall you mentioning whether it made a difference in the cabin temps and less a/c workload when you concluded in your test that the dash was noticeably cooler. Did you notice cooler temps from the vents?

 

So far, I've had my best mpg now that it is warmer. With my AC on set at 70 for a few minutes and then I switch to AUTO AC after 10 minutes of driving. My average mpg is between 53 to 55 mpg. Going to work seems to have more downhill to uphill so I've seen 61 mpg with my AC on at one point. Going home...my mpg drops to the lower 50's.

 

I did not test the air temps coming out the vents or in the cabin in general. I don't think that would be affected by the dash temperature. The air from the vents is controlled by the auto-AC controls. I am looking at the large, black dash under the windshield as a huge heat source that radiates heat inside the car, even while driving. No different than if you had a space heater running in the back seat. I assumed (always dangerous) that less heat from the dash results in a lower cabin temperature and thus smaller load on the AC and thus better MPG.

The fact that the air inside the car is warmer, from the hot dash, does alter the way the auto-AC controls the air flow so I guess the hot dash does, indirectly, affect the AC air temperature.

Then again, maybe I don't know what I'm talking about.

Bob