Has anyone ever tested the difference between A/C on and A/C off, on a dyno. My car feels like it has tons more power without that stupid thing on. Wish we didn't have humidity or I would leave it off. I am really just passing time at work while the boss is gone. Please run with this. No flaming only mean jokes or good info

 

yes, the HP will decrease with the AC on. The motor runs the AC compressor so of course your HP will decrease.

 

He was asking if anyone ever dynoed to see what the actual difference is...like 15 or 20 HP. Its gotta be a decent chunk of power as I can feel a big difference between the 2 also.

 

yeah im guessin at least 15.
to be truely noticable it has to be at least 10, and its a very noticable power decrease.
i wouldnt be surprised if it was as high as 30.

 

If its 30 that would blow simply because the damn AC in teh cars sucks.

 

how can it both blow and suck?

 

i notice it... it feels like the engine is bogging...

 

Apparently you've never met my ex...

 

when i go cruising its windows down 4 me no ac.... my girlfriend hates it because the wind messes up her hair.. but thats the price u have to pay for a win ... lol

 

That probably slows you down a lot too. Windows down creates a ton of drag...hence why its actually better on gas mileage to run theAC as opposed to your windows down on the highway.

 

they are normaly left half down... but nun the less u speak the truth..

 

It isn't as much as you think. When you're cruising at 60 in 5th gear the engine isn't developing anywhere near it's peak hp. Maybe only 15-20hp. At those levels, even 2-3 hp is quite noticeable, which I feel is a more likely loss.

Trust me, if your A/C were drawing 20-30hp all the time, your fuel economy would drop to 10-15mpg when it is on, possibly less...

 

When you're on a dyno, you're at wide open throttle. The air conditioning compressor turns off at WOT, unless for some reason you would change it.

 

It depends on the car, the temp, all sorts of factors. On the highway, some cars do better with the A/C, some do better with the windows down.

However, in the city, where you're going slow or starting and stopping, the windows will always win the efficiency contest. Mythbusters did a test where the car with the windows down won by a long shot.

 

I saw that episode too. Slow speed = windows down. I prefer the A/C though. No one wants to race my crazy ass LS

 

Did not know that about our cars. Good Info.

To the OP, that's the price you pay for driving a 4 cylinder car. Your belt driven air conditioner strains the engine. I big block v8 in a truck or SUV could probably run an AC as an afterthought, but not us.

 

OMG aint that the truth man.... I ******* hate that " hair is getting messed line " its such bullshit... That is when i start threatening to get a convertible then it would be top down chrome spinning and let the bitching begin.


Yea and it is way noticable decrease.

 

I did grow up on Long Island... SO I may have...

55mph is the threshold. Under that speed the drag coefficient is less than the strain of the A/C, above 55mph the drag coefficient becomes great than that of the strain created by the compressor. Personally I prefer windows open until I get on the highway, I just don't enjoy the loudness of open windows at high speeds. Thats when I put my AC on low for a couple minutes at a time. Not really a fan of AC

 

I don't like how mythbusters did the test, should have done it both ways in both vehicles. My parents both had 99 S-10 blazers, same options, same gearing and everything. My dad's blazer ALWAYS got better mileage, when they switched drivers..same was true. So if they wanted to truely test it they should have done both ways in both vehicles. Just because they look & weigh the same doesn't mean they are infact the same. (one could have engine trouble, clogged cat, plugged muffler, ect) there are alot of different factors.

 

Good point. Or from GM could be a slightly different tune

 

gm did a test years ago, this was probably back in the mid 80's. I don't remember what kind of car it was on, but they found running the ac cost 20hp.

that has to be taken with a grain of salt though. first off its not going to cost you 20hp crusing down the road at highway speeds (someone said you are probably only making 15-20 hp, I would say its probably a little more, but i'm sure no more than 35-40hp) so a reduction of 20hp would be like hitting the brakes. its only at high output here you would actually see a big decrease, like 20hp. If I remember correctly, the test was done on a fairly well powered car, one of the old land yachts, so it probably made at least 250hp to begin with. looking at it like that Its probably something like a 10% decrease in power, which tells a lot more than "20HP." the biggest thing is the technoliogy changes. an ac unit on a car from those days is nothing like a modern unit. the effeciency has increased by leaps and bounds, running an ac really doesn't hurt performance like it used to.

when I had an 87 grand national the ac made a very good engine brake to use going down hills, it just drew so much power to run. even on a very well powered car (in the neighborhood of 600ft/lb, hp on those cars is not a fair measurement) it really felt like i dropped a cylinder any time the ac was on. sure the ac hurts my cobalts performance, but its not all that noticeable.

my guess, I would say around 5% or less loss in power from the AC. so around 7-10hp...

 

you guys do realise that you're loosing power with the AC on or off, you have to disconnect the belt to regain ALL of your HP, you still have to keep compressor compressing with the AC on or off.

 

AC compressor clutch *cough*

 

Wow, think a little before posting something like that.

^^^^

 

you guys probably sit at stop lights in first gear with the clutch in too don't you.