TTCCC

I know AC uses more power and gas just turn only the fan do the same ?

RAAB3485

No it doesn't do the same because it doesn't have to drive the AC compressor when you just have the fan on.

ScitC

The AC does require more power/gas, but it is an insignificant amount, unless you are going 100+ for some distance (or near the cars top speed). Besides, you would rather be fresh when you go somewhere rather than being musty lol.

A fix would be a lighter crank pulley to compensate, but warranty would be an issue. Toyota also advises that balance issues are a problem with the lighter crank pulley, but I have yet to see a problem for myself.

Brandon

silverstreaktc

well according to the pep boys test, the windows down causes more aerodynamic drag, thus uses more gas than the A/C....

....and this is why they put up fake cameras in their stores and TELL PEOPLE THAT THEY'RE fake.



"These premises are being monitored by a no-circuit television"

FreedomOne

There was an episode of Mythbusters testing this theory.

BZinn1

I drove from Tacoma WA to Medford Or with AC on.........and drove back with it off........and got 350 miles onthe first tank and 335 miles onthe second tank........differance......about half a gallon on a tank of gas...........or $2............use the AC.........

ScitC

Silverstreaktc almost confused me....?

The tc sunroof will cause drag, but again, you'll have to be going far and at high highway speeds for an effect to really take place.

Brandon

engifineer

Well, since pulley weight has zero effect at steady state speed (actually you are removing inertia, thus making it easier to slow the engine down due to less flywheel effect.. however, crank pullies are insignificant either way) a lighter one will not effect this at all.

AC systems on newer small cars are less of a parasitic drag than older systems.. but it is definitely an impact. It will show up more so in stop and go traffic than on steady state cruising typically.. but it wont be a huge amount either way.

Technically, running just the fan does have an effect. Power in has to = power out in any system. So the power used by the electrical system has to be matched by the power used to charge the battery.. meaning the parasitic load of the alternator is higher when you draw more power from the electrical system.

However, that effect is very, very small.. so for the purposes of this conversation you can effectively say no.. it will not have the same effect as running the AC compressor.

engifineer

And I have issue with most tests between the AC or windows down, since it could vary wildly between cars. For example, I have owned cars that will nearly blow you away with the windows down. A old Opel GT, however, will smother you even with the windows down.. since nearly no wind enters the car (I believe those were the first cars ever designed using a wind tunnel as well...)... dont ask me why I know that about an Opel GT... or why I used it as an example... So I would venture to say that with the huge variation in the amount of power needed to turn various types of compressors.. along with the huge variation in aero designs.. it is hard to say from any one test which is more efficient overall.

I have driven many times to OK from MN in my tC (650 miles each way). I have driven the whole trip with the windows down and sunroof open and the whole thing with the windows up and AC on. I typically set my cruise at 80 mph or so the whole way. I have seen little to no variation in fuel efficiency on any of those trips. 29 - 31 mpg is pretty much always what I see overall for the trips

ScitC

I aggree about the alternator having to draw more work to make power for blowers etc, and that it is insignificant.

A lighter crank pulley will fix the problem for go and go, but not at steady speeds, it will do just the opposite b/c of inertia, that weight is used to help keep the crank spinning or cruising at a steady speed so you're right. Thats why I wrote A fix. But I should have explained it more in detail.

All in all, there is no real soultion. Engineers have made the AC and car work as efficient as possible today. Well, maybe there is, but IDK it lol.

Brandon