Reduced power with A/C on

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2010Civic

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On my 1998 Honda Civic whenever I turned the a/c on it felt like 25% of the engines power was gone. Turn it off and the engine felt a lot more powerful.

However on my 2010 Civic turning on the a/c makes absolutely no difference on power.

I wonder why this is? Is the a/c compressor a lot more efficient and takes less power to turn? Or is there some other reason?

The 1998 had a 1.6L engine while the 2010 has a 1.8L but is a bigger car and weighs more so I doubt that is the reason.

Thanks
 
You have engine drag caused by alternator and A/C compressor, 25% is huge though, I wouldn't think it would cause as much drag as a fat guy in the passenger seat.
 
Here's just a bit of what I've read about A/C systems in recent years.
When the throttle is applied enough, oh I guess about 2/3- WOT, to get more engine powed, the ECM turns off the A/C Compressor during this throttle aplication(throttle position dependent) so that the engine can get its needed power.

I am sure there is more to it than this.
 
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Well, your 1998 had 106HP, your 2010 has 140HP. That's a big difference. Also, the compressor on the 2010 is probably more efficient, making the difference seem even larger.
 
Another possibility is that the computer compensates by opening the throttle body more relative to your foot position with the A/C on. (one of the things made possible with E-throttles)

Not sure about honda, but I do know a lot of them do compensate to give the car a more consistent feel whether or not the AC is on.
 
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I bet your 2010 has an electronic throttle as well. When you are at part throttle, a properly calibrated electronic throttle can all but erase the drag of A/C compressor. Since the computer knows the A/C state, it can add and subtract throttle to match the additional torque loss from the compressor making it seamless under most conditions. With earlier systems the throttle position was strictly controlled by the driver and at higher loads an IAC motor can't do much anyway, so you got a "sag" when the compressor engaged and a "surge" when it let go.

All of the benefits of ETC get lost in the paranoia over "runaway" events where it either has a ill fitting floor mat pushing on the throttle pedal, or a driver who is really pushing on the throttle when they thought it was the brake. NEITHER of these has anything to do with electronic throttle control, it was just a convenient scapegoat.
I've seen these being tested in an EMC chamber, it's a sight to behold. The engineers were bombarding the vehicles with signals that would mimic parking right in front of a radio tower at the airport. It would blur the camera views from the interference, but the throttle kept on working as commanded. They are also some of the most paranoid systems I've ever seen. When I worked on gaseous fuels, the computer would detect the increased manifold filling effect of natural gas and enter safe mode many times. We had to re-calibrate the computer to deal with this.
 
A little off topic, but I wish Honda started using variable displacement A/C compressors. My Infiniti has a VDC and it's nice not hearing the annoying on/off cycling like in my Hondas. I remember reading that VDCs create less drag on the engine as well.
 
yeah man on my old 300SD diesel, the ac killed me. I already had a 5000 lb car with 125 horsepower and severe turbo lag. Add an old inefficient compressor design that was outdated even then, and I had a rough time when it came to keeping with traffic.
 
I agree about the computer adding throttle when you turn on the a/c to compensate. While the 2010 has more HP and is newer/fewer miles there is not even the slightest hint of power loss when you turn the a/c on. Not even when you are accelerating up an on ramp.
 
With either of our old Accords, a '97 LX (no VTEC) or the '99 LX (VTEC) you could feel the difference between compressor engaged or not, especially the '97, which had but a buck thirty out of its sixteen valve 2.2.
These cars had mechanical throttle control, of course.
You could compensate for this by using more throttle as well as holding a lower gear longer for more revs thus more power.
My BIL had a '92 Civic VX, the fuel economy model, which had ridiculously tall gearing as well as a ridiculously low reline. The AC on it dragged things down so much that you could use the AC button as a sort of brake, kind of like regen braking in a Prius.
As much as some four cylinder cars suffer from use of the AC, on a really hot day it sure is nice to have.
 
If you overcharge your A/C or raise to the really high end it will take more power to turn the compressor. Could be the old one was charged much higher than the new one. Contrary to what you would think more refrigerant is not necessarily better or colder. Making it harder to turn can cause efficiency losses.
 
Originally Posted By: mclasser
... wish Honda started using variable displacement A/C compressors...


They are indeed.

See this article

Quote:
To help conserve energy, the system employs a new Variable Displacement Compressor (VDC).
 
Old four bangers and ac never mixed in my experience. The 95 s10 I had you could feel the truck accelerate faster when you turned the ac off. I think I read somewhere that it takes around 20-30 hp to run the ac full blast so when you only have 100hp or less to begin with you notice it.
 
Originally Posted By: Char Baby
Here's just a bit of what I've read about A/C systems in recent years.
When the throttle is applied enough, oh I guess about 2/3- WOT, to get more engine powed, the ECM turns off the A/C Compressor during this throttle aplication(throttle position dependent) so that the engine can get its needed power.

I am sure there is more to it than this.



No more than this^ Older vintages did not cut the compressor.
 
Automotive A/C systems have gotten much more efficient over the years.

Back in the late 1960's they started putting A/C in everyday blue collar cars. They worked well as long as it wasn't too hot outside. When it was very hot, those autos started to overheat and it was necessary to turn off those A/C systems.

Things have gotten much better and today's systems are better than those of just a decade ago.
 
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