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Fuel Economy with AC ON vs AC OFF

1K views 8 replies 6 participants last post by  qaz996 
#1 ·
Does driving with the AC ON kill your fuel economy?

I lose a good 4 MPG (averaged over several fill-ups) when running the AC. I noticed this last summer too. I get better economy at highway speeds with all windows open and AC OFF. I did not notice this as much with my previous V50 (T5 FWD auto) vs present (T5 FWD M66). I have no service records from the previous owner. It was only serviced by Volvo for recall items, so they have no records either. I can tell the compressor was replaced. Could it be over charged?
 
#2 ·
#6 ·
Very interesting. I always heard the opposite but it always seemed like a wash in my previous cars, except my '94 Integra. The Integra made all its power at high RPM and had little low end torque. The AC really "sucked the life out of" the car in normal driving. There, I didn't say "Killed".
 
#4 ·
I think "kill" might be an overstatement, but sure, it does affect it negatively. You'd do better if you rolled the windows up, btw. The car is significantly more aerodynamic in that configuration.

Don't forget that the gasoline formula changes in the summer, and hot ambient temperatures affect mileage negatively, too.
 
#5 ·
Windows up and 95 deg F with AC Off... No thanks! Straight highway I get almost 34 MPG :) and that is calculated, not based on trip computer. My normal driving is a mix of 60% highway / 40% round town. Windows up and AC Off I get around 29-28 MPG. I see a small drop in economy with windows down and AC off (28-27 MPG). I get a much more significant drop with windows closed and AC On (24 MPG). Since all the data is taken during the summer months and I am running the same brand and grade gas, gasoline formula is not the issue. I can even see the difference in the trip computer "Instantaneous MPG" reading in real-time.

I mainly want to figure out if something is wrong with my AC since my previous V50 didn't seem to have as much drop in MPG and I don't know who replaced the compressor, where they got it or how it was charged.
 
#8 ·
It is normal to have lower than expected fuel-economy whenever accessories are being used, particularly the AC system. But then again our cars are designed to turn off the compressor whenever you step on the accelerator - to save fuel and for better throttle response. I do not find much difference in fuel economy on my 2.4i simply because when I use the a/c there are a few usual things I'll adhere to, such as when the air gets cold enough, I'll set/raise the temperature level up to 4-5 bars and making sure the 'recirculate' button stays lit! So...bad gas mileage whenever the ac is on? No, not really.
 
#9 ·
I live in a hot climate, so not using the A/C in summer isn't even a consideration. I'll pay the fuel economy penalty.

That said, many years ago and not in the Volvo, I made a very unscientific observation about fuel economy and a/c usage: I knew I should get about 330 - 350 miles per tank of gas. In the summer, when I was using my A/C, I noticed my tank range dropped to 300 - 320 miles. I then suffered through a whole tank of gas commuting with windows down and no A/C usage to test the effect of aerodynamic drag (windows down) on my tank range. It went back to the 330 - 350 miles range. This was a commute that was 90% freeway driving. It seems I debunked the theory that better aerodynamics (windows up) negates the effect of A/C compressor drag on the engine.
 
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