I do not know how much power the A/C in a car uses, but I can tell you this: Contrary to what some have said here, there is a VERY noticeable difference in available power, especially when accelerating from a stop. I have a 1.8 liter engine because I can’t afford that Mustang GT I want, and sometimes getting going on a hill is a challenge with the A/C on.
doubleclutch
I do not know how much power the A/C in a car uses, but I can tell you this: Contrary to what some have said here, there is a VERY noticeable difference in available power, especially when accelerating from a stop.
Then you may have some other problem. Accelerating from a stop you’re in low gear, which should be fine. Accelerating at higher speeds (in high gear) should be much more affected by the AC. That’s why some (most?) cars kill power to the compressor when you gas it in high gear.
My 1.4L Chevy Cruze has no problems going up steep hills with the AC on at highway speed. If I’m accellerating into the freeway, and “canning” it to get up to highway speeds (there are several entrance ramps here that were designed years ago and give you no space whatsoever to get up to speed.) the computer senses the load and temporarily cuts the compressor for me. I can feel it because the air from the vents gets warm. When up to speed and cruising, the air gets cool again. One more vote with the others here, OP is just wasting time and the lifespan of the switch.
@ok4450 The Ford AOD’s driveline loss was more that 15%. 15% driveline loss is more typical of manual transmissions (RWD applications). The AOD was over 20% IIRC.
I wasn’t for sure on the driveline loss of the AOD. The article had stated 15% but I have also heard that it’s higher than that based on other testing. I was going with the lower number so as not to seem like I was piling on. That’s a lot of grunt being lost between the engine and wheels.
Regarding the A6 compressors, many decades ago there as an old man around here who owned a late 60s Cadillac.
I’ve seen him running around on a 100 degree day and in all seriousness, the lower edges of the windshield and lower edges of the glass in both front doors were iced over to the point of not being able to see through them. It wasn’t frost or haze; strictly an interior ice storm.
The DeVille emblems should have been removed and replaced with Thermo King badges.
I tend to keep the AC in my car set at just this side of “meatlocker.” Drives my poor cold-blooded wife nuts. It’s not unusual for me to arrive at home from work at around 1am, get out of the car, and have my glasses fog over. 
“The DeVille emblems should have been removed and replaced with Thermo King badges.”
Didn’t Thermo King make them? They had a plant in Bloomington and I seem to recall something about making the GM compressors or visa versa.
It makes no difference on my Dodge Dakota,power to weight is very bad on that little piece of metal,these new compressors use very little power,I 'm suprised more car ACs are not electric and sealed .I guess if they did that.the failure rate wouldnt be high enough.
I’ll never forget the first time I took apart an A6 compressor and saw six cylinders and pistons in such a small unit.
I drove a few VW Beetles in the 1960s that had after market AC installed and when turned on at highway speed if felt like the brakes were being applied. But I agree that current model cars won’t benefit from switching off the AC when accelerating.
Completely unnecessary, and you are wearing out an expensive A/C component prematurely. Gas savings will not be measurable.
Thirty years ago with inefficient compressors you could buy a gadget that turned off the A/C when accelerating.
I have seen cars back in the day that shut off the a/c compressor under load. I thought that it was a PINA.
@meanjoe75fan, the cycling on & off wait time is something that I have only heard in reference to home a/c units. Depending on the temp outside, my Toyota compressor will sometimes cycle off & on every minute or so. My Camry is now 20 years old and my system has never been touched. The sight glass is completely clear (no clouds) and it is still ice cold in the Summer. That is one reason it is the travel car of choice in the summer. Our new 2014.5 Camry is lacking when it comes to the A/C department.
I recall that quite a few automobiles would drop the AC and alternater when under load. The operation of the system was very annoying to many drivers.
Let me see. I cannot give you an exact answer. But, we can play with numbers.
By memory, correct me if I am wrong, 1 HP is 746 watts, theoretically. Due to inefficiencies, and to make the math easier, let’s call it 1000 watts.
So, 40 HP would be 40,000 watts. That power of a/c in your house would require your own sub-station. And, you would need a 400 amp service just for the a/c. So, yes, 40 HP is not correct.
I am not sure the 6 HP figure supplied by one member is correct, but it is certainly closer than 40 HP. A 6,000 watt a/c is pretty powerful.
@irlandes The number given in the past was usually about 5 HP to power the A/C. Today, with more efficient compressors, it’s less, probably about 3 HP, depending on the size of vehicle.
One reason that the a/c can seem to really affect a car is that the engine is only making a small fraction of its max hp during most driving. So if the engine’s only putting out, say, 20 hp, and the a/c kicks in needing 5 hp, that’ll be quite apparent at that instant.
On my '81 Accord I added a vacuum actuated switch in series with the AC compressor clutch solenoid.
The switch was connected to manifold vacuum, so under heavy throttle and low manifold vacuum the switch would cut out the AC.
This noticeably helped acceleration. Not intended to save any fuel.
IIRC JC Whitney sold the switch for this purpose. It was even adjustable.
I added a tee to a vacuum line and also installed a vacuum gauge on the center console.
On my '06 Matrix I can feel the computer holding off the AC under full throttle and cutting it back in above a certain RPM.
Let me clarify my last post a bit…Texases hit it on the head. My car has a manual tranny, and at the 1,100-1,200 RPM I use while slipping the clutch to get going, my engine only has about 15 HP available. When I say “getting going on a hill can be a challenge”, remember that I live in Pittsburgh, where having to stop on a fairly steep hill is a regular occurrence. Once the clutch is fully engaged I just have to run the gears out a little more, but that initial start can be a problem.
When I went to the store tonight I turned my AC on for the first time this season. It didn’t seem like it was doing a very good job. When I got to the store I discovered my back window was open. No difference in power though.
I agree with you-all.