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Comment by grecy | Hacker News Reader

Wow, that is a massive hit to fuel consumption from the A/C. What gives?

Is it? The thing's huge, air conditioning is never cheap. A quick search says average cars consume ~25% more gas with AC, making it somewhat high.

I think short trips at low speeds are also terrible for AC, dunno how they did the projections.

A quick search says average cars consume ~25% more gas with AC, making it somewhat high.

Tons of websites say this but in my own testing during my commute the difference is almost unnoticeable, let alone a full 25%.

my car consumes 5% more with AC on. it's a 2002 Mazda. So, I don't believe 25% number.

My source was a government site, make of it what you will. I may have worded it more strongly than I should have. https://www.fueleconomy.gov/feg/hotweather.shtml

Consumer Reports did a study on this and it only reduced gas mileage by 3% on a Honda.

https://shop.advanceautoparts.com/r/advice/car-maintenance/c...

At 65mph and ~85 degrees. The page I linked sources several studies testing at many other temperatures and speeds.

No car takes a 25% hit from the A/C in gas mileage.

>The internal combustion engine (ICE) variant has an estimated fuel efficiency of 14.7 mpg‑US (16.0 L/100 km), decreasing to 8.6 mpg‑US (27 L/100 km) when the air conditioning is on.

It may be a “worst case, only when actively cooling at maximum power” figure. In reality you’d expect ambient conditions to make a big difference to aircon energy use.

I feel the same way. I've never had a vehicle that consumed more than 5% extra with A/C. With my current diesel I can't notice a difference at all.

No. Sorry the quick search result was dead wrong.

I think the numbers here are more like the expected consumption in actual mail delivery usage vs. something like the familiar EPA MPG ratings you'd see on cars.

A mail truck is going to be driving pretty slowly and stopping a lot, both of which will make an extra constant load like AC have a bigger effect.

Perhaps you can't use the auto-start/stop feature of the ICE system when the aircon is on? When the vehicle is stopped, something needs to be turning the compressor or things get hot pretty quick in hot climates. USPS trucks probably benefit from the start/stop system more than any other efficiency feature this new vehicle has.

AC ON with door open venting to the outside at all times, no air dam.

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