Cruiter

I think he might actually have a point with your temps set too high. But the a/c is very efficient and it will cool you down even with your outside temps. I'd try around 70-72 degrees and fully on automatic including fan speed. Just set the temp you want and let it do the work w/o further input. For the record, the stop and go driving your doing should actually help the efficiency if you practice trying to minimize stopping as much as possible by just slowing down early to avoid having to start from a stopped position. If someone lane jumps in front of you so what, you can smile knowing you're getting far better economy. Learning to drive the car for efficiency isn't hard, but it is an art and doesn't mean you have to go slow. It's mostly in how you slow down and start up.

Let us know how it goes. If you have a droid phone, there is an excellent app called 'fuelly' that will give you excellent info over time as to actual mileage and even cost per mile. It's a free app if you want to play with it.

DunWkg

Here's my thinking, the a/c compressor needs energy. That energy goes from the batteries, the batteries get energy from regeneration, regeneration is made possible from the motion of the car, the car has motion from the gas engine, having the a/c on increases the demands on the engine reducing gas mileage. This is the reason if in ECO mode the computer may reduce a/c compressor run time.

If its 110 outside and I have the climate control set to 77 degrees, the car needs to cool. If the temperature outside is 55 and I have the climate control set to 77 degrees, the car needs to heat.

Under some conditions, 77 degrees may feel comfortable for cooling. Under many conditions 72 degrees feels comfortable for cooling. Ambient temperature, humidity, wind speed (wind chill), your age, your weight are some factors influencing comfort. If I've been outdoors in 110 degrees and get into a car at 77 degrees and fan speed on high, that is going to feel good or cooling. However after riding in a car at 77 degrees for awhile that is going to feel warm and 72 degrees will feel better.

wa3cuj

I agree that the a/c does not hit the mpg for 4-5 mpg but it does draw power from the engine. Being powered by electricity, some form of energy is required for the conversion to electricity. There are only two sources of energy available, regenerative breaking and the engine which is fueled by gasoline. Unless you are going downhill 100% of the time the batteries will need to be charged more when the a/c is on than off. (I am using the phrase batteries to represent the overall electrical system in the vehicle.)

Just like running your a/c at home, some form of energy conversion is taking place somewhere to provide the electricity to run your a/c. Actually more energy is needed to to be converted than you use, because there are losses involved in production and delivery to your residence.

Sorry for running on with this. I have to take my old work hat off and remember that I am now retired and need to concentrate more on my golf game!

Cruiter

Bob, I'm thinking we're getting into discussions here for nothing more that to see who winds up with the last word. Operating the car in any mode uses more gas than leaving it parked. I know you'll enjoy your golf game but the extra body energy you use will probably raise your electric bill at home to cool you off and you're water bill will go up when you shower off the sweat.

The vast majority of people here that drive the RXh will agree running it in the summer with the a/c is the most efficient time of the year for it. And if your out for the last mile, then let us know hot it's going w/o the a/c on.

Not trying to wind you all up, just saying Lexus designed the car to run in the most efficient way possible with a/c, heat or whatever climate you want to create inside the car. And for a car of it's weight and power and size and features and luxury I don't see any competition anywhere at any price.

DunWkg

...but that old work hat is so comfortable...

Excellant points Bob. An RXh is not the perfect Rube Goldberg machine. Everything you do, with perhaps the exception of opening the hood, consumes energy possibly at the expense of mileage. Nope, nope I'm wrong, opening the hood involves the computer "knowing" you opened the hood. Gosh when the RXh just sits there in the garage all the clicking, buzzing or whirring, even the remote keyless entry is at the expense of mileage. An infinitesimal amount...

DunWkg

Jim, excellent point. My point is turning the a/c off is more efficient. That is why the car does it in ECO mode. Efficient and comfortable don't always go together.

Great discussion!

GoHuskers

I think BAM made good points. I always set my AC on LO and start out with high fan speed then reduce it to 1-2-3 bars depending. My tires are about 35/38 PSI cold/hot and my mileage is great in City and good on HW (31/28) (of course it is NOT that hot in the midwest yet.

Note: When the humidity is high and temp is high (100 F) the mileage REDUCE.

Ciege

Well well well... I think Bam may be on to something...

Set the AC to "Lo" on my drive home. It was a bit "colder" out today only hitting 104 on my drive home... :-) All other conditions were relatively the same. My MPGs on the trip home ended up being 27.4, which is about where I would expect them to be using the AC versus no AC. (I do have an AWD so that lowers my overall MPG from you FWD folks).

So I believe my thinking on how the AC works in a car compared to a house was flawed. I didn't realize that the car tries to blend the temperature and push out 77 degree air as opposed to cool until it hit about 77 in the cabin then turn off the compressor.

I'll keep the experiment going for a bit and see if I can maintain or increase the 27+ MPGs I got yesterday afternoon.

Thanks All!

DunWkg

Ciege,

It's unlikely, although possible, your home uses automatic control of outdoor air for ventilation. A difference between your home's heating/cooling system and the heating, ventilation and air conditioning system of your car.

Good luck with your experiments.

wa3cuj

Jim,

I'm thinking that I might have offended you some how. That was never my intent. I was trying to address your comment that your a/c takes zero power from your engine. If in some way I came across as lecturing or saying that you were wrong, I sincerely apologize. I enjoy your posts on this board.

GoHuskers

Yesterday I started with "almost" full battery, it was hot (92F) and the car was seated for 3 hours in the sun. I started out at LO and in AUTO mode so FULL BLAST FROM THE AC. A very short drive later the battery indicator was in PURPLE so the engine was on and it was hard.

With this experience I believe when it is hot and AC is in full blast it will rob you some MPGs (because engine is on more often than without AC).

Cruiter

Bob, no offense taken. It just seems there is a lack of understanding re: RXh economy. Your point is valid in a technical sense but it doesn't always work that way. If you set the a/c to operate totally in automatic and set the inside temp you want to get it to regardless of the outside temp summer or winter it will really keep you comfortable year round that way. When you're actually driving down the road at speed the time the engine actually shuts down will be very minimal and depend more on the amount of power needed to keep the car at a given speed or needed for extra acceleration then whether or not the a/c compressor is running. Because it's (ICE) running anyway the batteries will be kept charging and discharging (as designed) to supply additional horsepower to the wheels. The amount of extra charging to run the a/c is nothing you'd ever notice unless you're keeping cool in the parking lot while your wife is shopping in Macy's. And I guarantee you her shopping will be the biggest economic hit . In the area of the cars performance compared to the RX350, I'm absolutely correct, the a/c does not take any power from the engine. Even if you floor it with the a/c at high, the motor/generator will be throwing juice at the traction batteries and they will be throwing 25 extra horsepower (295 450h vs 270 standard 350) to the driving wheels regardless of the operation of the a/c compressor. It does not/will not suck horsepower. It can't!

I hope this clears up the picture some for a complex and wonderfully designed hybrid system.

One other point to consider in the operation of the car. For the last two years I've driven with Eco OFF !!! I'm getting slightly better economy and the a/c operates more like in a conventional engine operation. I merely adjust my throttle response to a lighter touch but when I want 'vroom vroom' in a hurry it's there
Just sayin

DunWkg

Jim,

Some excellent points. Thanks.

I found this discussion on a hypermiling website:

(http://home.earthlink.net/~poliakonia/id12.html)

Your examples demonstrate what that author is saying.

robartin

Interesting blurb quoted from the referenced site. I'm definitely noticing the hit on MPGs running the AC. You can see the draw on the traction battery clearly if you sit in a parking space for a few minutes with the AC running - the battery runs down fast. There's also a noticeable MPG hit when running the heated seats.

Droid13

An older post, but when it popped up and I read through it, I couldn't come to terms with this statement. While it is true the A/C does not draw power from the engine, it still draws power from the hybrid system as a whole. System power (ie the ICE, generator and the battery) is what provides the 295HP rating, but that assumes the battery has an acceptable level of charge and there is no other significant draw of power, like an A/C compressor. The "system" has a set limit of the amount of energy it can provide, if the A/C is running and drawing energy, that takes away from the energy available to move the vehicle. Hybrid systems don't create free energy or have a special reserve for the A/C.

Now that said, in practice the hybrid computer may automatically turn off the A/C compressor during situations of full acceleration (as with conventional cars, many of them automatically release the clutch on their belt driven A/C compressors during full acceleration or when starting the vehicle).

It's a fact of life, A/Cs rob energy that would otherwise be used for moving the vehicle, hybrid or not. Exactly when and how that energy is used will affect vehicle performance and mpg, but fortunately that is really why hybrids are generally more efficient, because they are much more capable of controlling when and how energy is used.