Hot climates & AC & Gas mileage

[TheLandYacht]

Anyone else notice that running the AC gives a SERIOUS hit on gas mileage?

Like, to the tune of 6-7 MPG?

I live in Central Texas where it's not unusual to sit at or around 100degrees Fahrenheit. for weeks/months on end. So running the AC is a must.

I noticed the trend when I stopped running the AC at night when the temps dropped for a while & my MPG improved DRASTICALLY!!!

[Mirageman38]

Yes, same thing with going up hills, lots of stops signs, Texas 70+MPH speed limits, or stop and go traffic. All will take a pretty serious hit in the MPG.

[TheLandYacht]

Yes, same thing with going up hills, lots of stops signs, Texas 70+MPH speed limits, or stop and go traffic. All will take a pretty serious hit in the MPG.

Yeah...but that's nearly 20%. That seems a bit excessive. In the prius, the hit from the AC was closer to 3% even in the dead of summer driving across the state under the direct sun. In the truck, the gas mileage sucks so much already, I don't know if you even notice it.

[Mirageman38]

Something I seem to notice is the engine likes barely being taxed, anything that even mildly starts taxing it takes a big hit on MPG. Not sure if mine is 20%, but I don't normally have 100 degree temps.

[defensivetackle88]

Yes and I say normal.

Lately, it has been over 90 degree here (heatwave in effect for now) and I have been driving around the city below 45 mph and more idle during my short trips wherever with the A/C blowing 61 degree with auto recirculation being on and my MPG drops to 34.

It only temporary. On a nice day cruising at 55 mph without A/C, I would hit 50! 65 mph yields 45 or better. I still love my Mirage more ever than my past cars.

[TheLandYacht]

...It only temporary...

BAHHAHAHHAHAHAHHHAHHAHAHAHH!!!!!!!!!!!!!!!!!

This is Central Texas, where we go 3-4 months in a ROW where the temperature doesn't drop below 100 degrees during the day.

...EVERY DAY.

And then it's ALMOST as hot for another couple of months before & after that too.

so..."temporary" is a bit arbitrary.

[7milesout]

Yeah...but that's nearly 20%. That seems a bit excessive. In the prius, the hit from the AC was closer to 3% even in the dead of summer driving across the state under the direct sun. In the truck, the gas mileage sucks so much already, I don't know if you even notice it.

Question: Isn't the A.C. / compressor disconnected from the drivetrain in the Prius? If so, this would be the reason it doesn't drop ... or drop so much on the Prius.

I have limited experience with the Prius, just drove them when I worked at the Toyota Technical Center. But say your driving the Prius on a typical Texas balmy 100°+ day. When that car is approaching a stop, the engine typically turns off. Yet the A.C. keeps right on cooling. That tells me that the A.C. compressor is not powered by a belt on the engine. But probably turned by an independent electric motor.

The drop in mpg on the Prius due to A.C. use would have to be due to the increased run time of the gas engine to charge back the batteries due to the increased electrical drain of a motor turning the A.C. compressor.

And yes, I think the loss due to A.C. use on the Mirage is quite large. Much larger than the additional drag of rolling down the windows. If I can roll with the windows down and NOT sweat, that's what I do. I use A.C. very little.

[mohammad]

Question: Isn't the A.C. / compressor disconnected from the drivetrain in the Prius? If so, this would be the reason it doesn't drop ... or drop so much on the Prius.

No such thing as free energy, being driven direct by the engine or by an electric motor would not result in the compressor being more or less efficient. The primary reason its electric would be so that when driving downhill or possibly idling for extended periods of time the Gas engine does not need to be turned on. Whereas our mirages also would not use gasoline by entering DFCO when going down a hill with A/C on.

[7milesout]

I think you missed my point. Maybe I didn't explain my point well. While I 100% agree with your explanation (already knew that), it is at all those times that the gas engine is shut off with the Prius, that it would get warm on the inside if the A.C. compressor was driven by the engine. Compressor efficiency was not my point.

[mohammad]

I think you missed my point. Maybe I didn't explain my point well. While I 100% agree with your explanation (already knew that), it is at all those times that the gas engine is shut off with the Prius, that it would get warm on the inside if the A.C. compressor was driven by the engine. Compressor efficiency was not my point.

This is true, Although all Toyota hybrids(corolla, prius) ive ever seen have an eco climate control button as shown here: https://attachments.priuschat.com/at...l-Feature.jpeg

my understanding is with this on it will allow the cabin temperature to be within a reasonable margin of the desired temperature when "idling", generally speaking assuming ambient temps aren't very high this would result in minimal or no compressor running while the car is "idling".

Another interesting point id like to bring up is the Mirage is offered with auto stop and go and will shutoff at a stoplight. It has the same A/C system as us. I guess the cabin control system is able to restart the vehicle on those models: https://mirageforum.com/forum/showth...-2L-CVT-Mirage