I thought I read somewhere but can't seem to find it that the A/C compressor on the hybrid isn't run off of engine power but from a separate battery and thereby helping to reclaim a couple of percentages back to mpg. Can someone confirm?

 

correct. it has a compressor that does not require the engine, because by nature you cant have the AC stop when the engine shuts off at stop lights

 

Richard, like Josh said it's totally electric. In fact look under the covers over your engine. No belts taking engine power at all. A/C, power steering, all electric. Plus you don't have a belt turning the valves anymore. They're chain driven internally like Porsche's so no belts to replace. All part of making the RXh less expensive to maintain .

 

That's good to hear especially now that summer is approaching. We can use the A/C and not worry about the A/C robbing us of a small amount of mpg.

Here's to colder and more comfortable driving.

 

I beg to differ with that... It may be electric, but the AC saps about 4 - 5 MPGs from me. I've verified this by driving the same route, same time of day, etc... here with similar temps (within 1 - 2 degrees).
AC On I get 24 - 26 MPG from work to home. (this sucked when its 110 degrees outside!)
AC Off I get 29 - 31 MPG from work to home.

 

It is more efficient that a belt driven system but it will still hit your mpg unless you can find some way of keeping your batteries charged thru regenerative breaking only (like just going down hill). Lexus tries to help this situation by using the ECO mode. However, I have found that in my area, using ECO mode on hot summer days does not result in sufficient cooling for my tastes.

 

Chris
You have winter and summer seasons. In the winter the batteries get cold and the whole car including the core temp of the batteries needs to warm up before they deliver the best performance. I can't say how you drive your car, I'm not in it. But the vast majority of us get the best mileage in the summer. I can tell you my a/c is always on and it draws zero power from the engine. I've had it for nearly three years and 38,000 miles. It does NOT sap 4-5 mpg from 'me'.

 

Same here. I've seen mileage increase while driving in stop and go traffic with the A/C blasting. Big difference from the winter months when getting decent mileage is a distant second to having heat

 

That seems like a pretty steep penalty for using your A/C. I'd def have to ask you to check a couple of your settings. Do you have the Eco mode set to on? Do you have the air set to reciculate the air as this helps cool the cabin quicker and helps keep the cabin cooler? This helps the A/C compressor not work as hard and therefore not draw too much energy from the batteries. This in turn helps reduce the need of the engine to replenish the energy into the battery (unless you're doing plenty of regenerative braking). Are you running the fan on high speed?

 

ECO Mode is on.
Recirc is on.
Fan is usually on high to keep up with the temps.
A/C is set to 77 degrees for both driver and passenger.
I leave the seat ventilation off.
Tires are now at 38/40 (cold/hot), the dealer bumped up my PSI saying it might help with the mileage.

I drive mostly in stop and go freeway (rush hour) traffic. I try my best to keep the needle in the green (so to speak). I also try to switch on EV mode as often as I can while driving, although when the temp hits +100 (or somewhere in there) it never lets me turn EV mode on, always says EV mode is not available (even when I have full bars or missing just 1 bar).

 

I think I've found where your problem lies. You got the temp set too high. You're saying it never gets cold enough and it's in 110 degrees heat. That's because you go the A/C blowing at a pretty high 77 degrees in 110 degrees weather. You're never going to feel cold with that temp setting and so the A/C unit is constantly blowing at high speed. In my case, I always run hotter than my wife and so I want the A/C blowing med-high whereas she likes it on low. In her 450h, we start off med-high to get it going but then I have to turn it down to low because it gets quite cold in the cabin.

I'd start with putting the temperature setting lower to match what you're trying to accomplish and that is cool the cabin. Remember, running the air conditioning unit technically removes the moisture from the air being blown. That's why it's called an air conditioning unit because it "condition" the air. When you set it to low and all the moisture is pulled out of the air being blown in, it just makes it "feel" cold. It doesn't necessary blow in cold air. It's still drawing the air from the outside.

One more thing to add. Because you've got the temperature setting so high, it's almost in the "heatting" category, maybe the car is thinking that you're trying to run the heat and so the engine is running more often than it needs to be to generate the "heat" to put into the cabin. Then by you adding the A/C, the heat has the moisture removed and you have cool air coming into the cabin. This is my theory because most people seem to say that in the summer, their mpg goes up. I'm guessing because less time is require for engine heat up since it's hot out and because the batteries can get up to operating temperature quicker. On the flip side, it's my understanding that in the winter months, mpg suffers because it's takes longer to heat up the engine and longer for the batteries to get up to proper operating temperatures. Also, I believe the manual says something about using the heater especially in the winter months does negatively affect your mpg.

 

Hmmmm, interesting. So you are suggesting I set the AC temp to Low (as low as it goes)? I will give that a shot on my drive home today and report back tomorrow.

Thanks...

 

Yes, I would push the cold setting all the way down to where it says Lo. I'm guessing if you have the fan maxed out, at some point, you'll be reducing the fan speed because it will get quite chilly. Especially because I don't think AZ is that humid. More like Las Vegas weather and nothing like Florida weather.

(Don't take this the wrong way but) Why would you have it set at 77 degrees in the first place in 110 degrees heat?

 

Yeah, pretty dry heat right now. It does get humid in August though. Still not Florida (Orlando) humid!

Not taken the wrong way at all... I thought of the AC in the RX much like the AC in my house. I wanted to get to a comfortable set temp and turn off the compressor thus reducing power by not needing to make it snow in the car! Maybe my thinking is wrong when it comes to automotive AC versus home AC.

 

I see your thought process but it is my understanding that in the car you keep it that 77 degrees, the car will mix in hot air generated from the engine to maintain that temp but kick in the A/C compressor to remove the moisture from the air. I think we can confirm this by setting it as hot as possible and I'm pretty sure you're going to get hot air without the moisture if you keep the A/C setting on.

In the home, I believe it's an all or nothing setting. In other words, if you set the A/C unit to run, it'll run with "cold" air pushed throughout the house (if you have central heat and cooling) until the thermostat is cooled to your set temperature.