Druha

please dont scold me saying that the answer is already in the manual.

I'll keep it short,

when i press auto on my climate control..a/c light will always go on (even when its freezing outside) . A guy at my dealership has told me that it is just the compressor and not actually putting cold air, which is true. but will this affect my mpg?

and he said to leave that a/c on so it will prevent mold build up in the a/c system.

onepointon

I dont think it should have too bad of a negative affect on MPG. The system is designed to operate that way so I would just let it do its thing. I would imagine if you were to have mold build up and still be in warranty, it wouldnt be a problem.

My IS300 does the same thing. I haven't noticed any lose of MPG now that I think of it. I would just leave it be. Either way though, I cant imagine youll be hurting anything.

love_lexus

I always have my auto on, and one of the main reasons that I chose ES350 over IS350 is because it has this auto climate feature (like GS has) but IS350 doesn't have.
With auto on, it's really nice when you drive behind a polluted car, because it can automatically switch to internal circulation. I don't know how bad it will affect MPG, I always get 23.5 - 24.5 with 75% highway 25% local daily drive.

toneman

I guess one unscientific way of seeing if having the A/C set to on/auto has an effect on fuel economy would be to find a nice long flat stretch of road (preferably w/ no wind), set cruise control to some fixed cruising speed (e.g., 65 mph), then cruise on down the road and make note of the instant MPG reading on the display, trying to keep the MPG reading fairly stable (i.e., little or no fluctuation in the reading)...then turn on the A/C and see if the reading drops.

MD350

I put mine on auto, but then go to the climate screen and hit the A/C button off in the winter. So, I should not do that? I do the same thing on my wife's Pilot. Why run the system in the winter? I hear the clicking and the cooling fan running when it is on and don't see a need in freezing temps.

PsychDoc

That's exactly what I do. Why should the A/C condenser be engaged when it's below 60° outside? It's silly and I'm sure it would cut down on you gas mileage.

ESsearch

The AC will dehumidy the air while the heater tends to add humidity. By blending the two operations (as counter-intuitive as that seems) the air can be more precisely controlled. It will also make it much easier to keep the windows clear. Newer AC compressors are much more efficient than the ones even 10 years ago and I'd be surprised if you would see a 1 mile/gal decrease while running it.

Pete

Druha

Good so i'm not the only one who does this..
lol the weird thing was as soon as after I started this thread..every once in a while now when i hit auto. the a/c light DOESN'T come on. oh well i'm not really too concerned enough to do that test...maybe the next time i go on a road trip.

Glad to know a/c compressors have gotten more efficient. i was too used to my 1989 mercedes' broken a/c