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Is it normal to lose 15+ MPG running the AC nonstop?

6K views 29 replies 15 participants last post by  retepsnikrep 
#1 ·
I drive the same route every day with a few minor changes and average 220-240 miles per day. It is about 50/50 on city/freeway driving.

When I drive without AC, I generally get 68-71 MPG overall.

When I drive with the AC, I average 53-56 and sometimes even lower (like today when it was 115). On my afternoon route (when the compressor literally never shuts off), the mileage is sub-50.

I realize that the compressor running continuously will cause a major hit, but I'm wondering if this is abnormallly high. The engine really seems to struggle at times.

The difficulty in getting into and staying in lean burn is also an issue as well. Generally, I can only do it on the freeway.

Mainly I'm worried about the AC compressor, though, and whether or not this huge MPG hit is simply a fact of life or if I should have it checked out.
 
#3 ·
I would agree with the above statement.

CVTs don't have lean burn. :mad: However, according to our experience over the last 8 years, perhaps our lean burn-deprived CVTs don't seem to suffer the mileage hickey using A/C that MTs do. I say this based on the fact our CVT Insight has over 53K miles now, and except for a few (fewer than ten) times that My Beloved or I have driven with the windows open, due to a stunningly beautiful day or somesuch, we have had the A/C turned on with a setting of Econ/72° and the fan on two bars (out of four) continuously since January of 2001, when we acquired it new. She drives it like a Civic, although I at least try to achieve maximum mileage and drive it 90-95% of the time. Yet our LMPG is right at 55.6, which is within a stone's throw of the original estimated EPA highway mileage. So apparently the use of A/C is not such an onerous mileage penalty.

MTs always get such fantastic mileage compared with us slushboxers. Seems to me the difference in mileage wouldn't be 10-15 mpg... unless the use of A/C impacts your ability to enter into lean burn and its fabled mileage-enhancing properties. Otherwise, you're "just" driving a 55 mpg economy car...

Surely others will chime in with some intelligent observations... :)
 
#4 ·
AC mpg effect

I agree with the last post. Most loss is probably due to the loss of lean burn. I would guess you are losing 10-12mpg due to this and 3-5 from the actual AC usage. It rarely gets much above 80 here, but when it does and I try out the AC, I have a heck of a time getting into lean burn. The smallest incline or even a rougher road surface knocks it out. I guess its like driving at 10 or 15 miles per hour faster, the extra wind resistance is similar to the AC burden.???
 
#5 ·
i'll jump on the boat, and agree with all of the above

it rarely, if ever, gets up to 115 here, but whenever its hot out and im on the freeway. i keep the windows up, the climate control in econ mode with all 4 bars of fan, and the setting to either face, or face and feet. this gives me as much air blowing on me as fast as possible to help keep me cool. i also turn on recirculate to keep the cool air in the car. and i cycle the a/c manually. turning it from econ ac off to econ ac on and back. i will turn the a/c on when going down a hill, or if necessary, when coasted on a level surface. whenever possible, i will make sure the a/c is off when going up a hill. recirculating the air helps keep cool air blowing at you for at least a short time in between a/c bursts.

whenever im off the highway, i keep the same settings, but with econ ac off. and rolling the windows down.

max mpg is achieved(mythbusters proved it) by a/c on the highway, or above a steady 35-40mph, and a/c off the highway

of course, this might not work at 115 degrees, lol
 
#6 ·
In order for me to lean burn at highway speeds with the AC on, I have to draft off of another vehicle.

Where I realy hate using the AC it is around town. It's impossible to drive the car reasonalby without useing a fair amount of IMA under these conditions. Enough consecutive days of in town driving with the AC and I'm in forced regen.
 
#7 ·
Well, now that the Texas temps are hitting triple digits on multiple consecutive days, and birds are spontaneously combusting in mid-air, you have to have your A/C on. You just have to. I guess I'm getting too comfortable in my old age for anything else. :rolleyes:

For decades, I've wondered why manufacturers never seriously considered an easily-replaced, lightweight electrical motor to power the A/C compressor, instead of a difficult-to-replace, belt-driven pump sapping energy from the ICE. I just know there are wonderful, common-sense, financial and technical reasons for it, but I can't think of many. It would eliminate complexity, extra belts, tensioners, weight... In our little cars, I'm surprised Honda didn't do it from the get-go... :confused:
 
#10 ·
For decades, I've wondered why manufacturers never seriously considered an easily-replaced, lightweight electrical motor to power the A/C compressor, instead of a difficult-to-replace, belt-driven pump sapping energy from the ICE. I just know there are wonderful, common-sense, financial and technical reasons for it, but I can't think of many. It would eliminate complexity, extra belts, tensioners, weight... In our little cars, I'm surprised Honda didn't do it from the get-go... :confused:
Actually Honda did it in the Civic Hybrid. And went a step further: it's dual-drive, electrical and mechanical, and I believe variable-rate. I suppose the reasoning is that it's more efficient to run AC directly off the ICE (no losses converting to electricity and back) as long as the ICE is running, but Autostop can still be used because the AC switches to electrical when the ICE is off.
Not sure how the Prius II and III manage AC.
 
#22 ·
Ya know how if you are stopped and you turn the wheel, it will spring back a little when you let go? This is the residual "spring from the tires. If you turn the wheel and hold, it will take power to do that and the EPS would draw some current. Once you let go, the EPS power draw would go back down to nominal, or idle current draw.
Most power steering works on a torsion bar "like" system. If there is input at the wheel, and the tires are not aligned with that position, there is torque on the torsion bar in the steering system. The input and the output of the torsion bar are not equal. This difference is what gives the system something to amplify.
In hydraulic system, there is valving that directs fluid to one side or the other based on the input and output. To be honest, I don't know how the EPS works. Very similar I'd guess to how a servo works in RC. There's probably and input and output potentiometer on each end of the torsion bar. If there's a difference, it sends power to a motor to turn the wheels in that direction. When the 2 sensors match, there's no difference, so no power used (other than the idle power consumption of the circuitry.

BTW, I agree completely, the gen 1 insight is light enough it didn't need power steering. :) My '89 CRX Si doesn't have and it's pretty easy to turn except when totally stopped.
 
#23 · (Edited)
For INFO:
The operating principle of the EPS is basically the same a hydraulic power steering except for the following:

A torque sensor mounted in the steeering box is used in place of the valve body.
An electric assist motor is used in place of the hydraulic power cylinder.
The EPS controle module is added.

The torque sensor senses the road/tire resistance and the turning direction of the steering wheel and sends a signal to the EPS module. Based on that signal and the "speed sensor" signal the EPS module determines the required current and sends that current to the EPS motor. Then the motor turns to move the steering rack right or left.

(I'm in the process now of mounting an Insight EPS steering box (rack and pinion) with module on my "dunebuggy". Will let you know how it works out.)
(I predict that within the next 5 years you will see most cars have switched over to the EPS instead of the hydraulic system.)

Willie
 
#24 ·
I'm sure you've had enough feedback, but as a new owner I noticed the same thing. Turning on the A/C is like dropping an anchor. The a/c works great, but forces me to use lots of assist, and makes it harder to get into lean-burn. I ran the a/c on my ride home when I bought the car. 140 miles with the a/c set on econ at 78 degrees, and I still got around 65mpg.

It is sooooo much easier to drive this car correctly with the a/c off.

Regards,
 
#28 ·
I own a geo metro and man, you can feel it when the ac cycles on. I have wondered if a different pulley size would help or not since the vast rpm range it runs. It has manual steering,

Having said that, since I tinted the windows 20% rear 35% front realy helped to make it cooler and need less ac.

Infact I just did my front 2 windows 35% in my new insight and put a seconding coating of 35% film on the outside of the rear hatch.

Man, I use to run ac on the top speed, now half way is fine and cool.

You can find precut film online for about 50 bucks and its easy to install. If you tint it really dark and illegal, a cop has to find something else to pull you over and all you have to do is remove it. Man people in the show circuit just pay the ticket for the price of looking cool.

I did mines myself with film from walmart. 20% is really dark at night and can make it harder to parallel park. Forget the 5 or 2.5% stuff.
 
#29 ·
i've noticed that setting the A/C on 75* and turnin the fan to 2 bars, gives a good combination of good mpg and comfort level. Since the a/c isnt set to 60, it cycles the compressor less ofter, letting the car in lean burn longer.

This is in 100 degree texas summers, where even setting it to 80 degrees, cools the car a little
 
#30 ·
The AC is an mpg killer. I NEVER have it on at all, and just open windows by a couple of inches if reqd.

I don't live in Arizona though but in the fairly cool temperate climate of Northern England.

I'm an obsessive mpg nerd as well, and am happy to sweat in the name of fuel savings!
 
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