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climate control off

THE BIGPUNN

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THE BIGPUNN Enthusiast

THE BIGPUNN

Posted
Posted

i have always driven with the climate control on. i averaged on a 26 gal tank, 230 miles or a lousy 9 mpg. over this past week the weather has been great here in MI. mid to high 70's and sunny. i have turned off the climate control except in the morning due to some foggy windows. i have noted a change. i now seem to get 270 miles on a 26 gal tank, or almost 10.5 mpg??? due to the increase in gas prices i used to drive to work on a 5 miles stretch 70mph in a 65 zone with cruise control. i now drive 65 mph in the 65 zone still with cruise. i drive to work 3-4 times a week. otherwise my driving has been the same. anyone else expierience any climate control differences with mpg?

Jester4736w Enthusiast

Jester4736w

Posted
Posted

I've always wondered the same thing, bigpunn... I know that Air Conditioning will decrease fuel economy, because it uses the A/C pulley to run the compressor, so that's understandable, but when I had my 03 Chevy Cavalier, when I turned on the A/C the little green light would come to say it was on, and i could hear and feel the difference of the A/C draggin on the little motor. Then when i turned the A/C off and the Window defroster (Front) the A/C light would come on also. IDK really what I just said there, it's confusing, but now im affraid to use my d**n window defrsoters (front) cause of gas prices.

 

I guess, i just gotta stop thinking/worrying bout the d**n gas, or else i'll drive myself crazy!

Supurban Enthusiast

Supurban

Posted
Posted

Here in San Jose, the weather is nice enough to drive around with the windows down and many times just running the vent with no AC. I manually handle the fan and vent positions instead of letting the auto climate control do things.

 

It is possible to run auto vent with no AC by pressing Auto first then hit the snowflake (AC) button. That way it attempts to hold temp but without the AC. If it gets too hot and goes runaway, you will have fans blowing full blast - but then you'll feel the heat before the auto climate does.

 

My AC compressor engages even if the temperature is pretty mild out and the temp in the truck is the same outside. Compressor engaged means drag on the motor and some impact to fuel economy - most impact of course would be in traffic.

 

So my guess is it is best to simply turn off the AC when you don't need it - auto or manually.

SS Crew Enthusiast

SS Crew

Posted
Posted

I paid for auto A/C and dang it, I'm gonna use it when I want and where I want. :wtf:

 

Also you need the A/C on to defog the windows - it dehumidifies the air. :shakehead:

vhato Enthusiast

vhato

Posted
Posted

According to AutoTap, my trucks computer pulls up to 4 degrees timing advance when A/C is Active. However, the PCM adds extra fuel to make up for power loss and to keep the engine and exhaust cooler. My 2500HD w/Vortec 6000 looses 1.75 MPG when A/C is active. Basically 2 MPG.

 

The HD line of trucks appear to waste ALOT of fuel from my research on other PCM aspects to keep everything cooler. I assume this is because these trucks are expected to work hard without excuses. I plan to connect AuoTAP to my fiancee's '05 Crew Cab w/Vortec 5300 and verify if her PCM does the same, cut timing-add fuel senario.

 

The Engine Management on all GM trucks (1500, 2500, 3500) also has "bascially" 3 timing tables. 0-2000 RPM, 2000 RPM-4000 RPM, and 4000+. I can see the PCM attempts to use more timing and less fuel below 2000 RPM and MORE fuel and less timing above 2000 RPM. This is by design for whatever reason...Again, I assume to keep things like the Catalytic Converters, Engine and Exhaust cool. So keep RPM's in mind when driving.

71GMC_3/4T Enthusiast

71GMC_3/4T

Posted
Posted

Here's a weird thing I've noticed:

When driving home, I have a long (~3/4 mile) hill that is sloped enough that you can coast down it without losing speed. I've found that if I turn off the A/C, it jumps the DIC MPG reading by about 10 mpg from about 30 to 40. Now the really weird thing is that if I shift into N on the way down that same hill, it will go up to around 50 mpg with A/C on, and 99 mpg with the A/C off!

 

Apparently, if your foot's off the throttle but the engine is holding back the tranny, it's dumping fuel in. This must be to keep the engine cool like stated above.

 

Is there any damage that can be done by coasting down hills in N with the A/C off? I think I could get my MPG one or two better by doing this routinely...

vhato Enthusiast

vhato

Posted
Posted
Here's a weird thing I've noticed:

When driving home, I have a long (~3/4 mile) hill that is sloped enough that you can coast down it without losing speed.  I've found that if I turn off the A/C, it jumps the DIC MPG reading by about 10 mpg from about 30 to 40.  Now the really weird thing is that if I shift into N on the way down that same hill, it will go up to around 50 mpg with A/C on, and 99 mpg with the A/C off!

 

Apparently, if your foot's off the throttle but the engine is holding back the tranny, it's dumping fuel in.  This must be to keep the engine cool like stated above.

 

Is there any damage that can be done by coasting down hills in N with the A/C off?  I think I could get my MPG one or two better by doing this routinely...

 

 

 

 

Maybe, Maybe not. I think you will just get inaccurate DIC recults. The DIC uses data collected by the LTFT (Long Term Fuel Trims), DFCO (Deceleration Fuel Cut Off) and other variables. That is why the Inst Economy DIC setting is always bouncing 3-4 MPG. One look at the PCM's LTFT's will show you bouncing between Rich and Lean with a 10% loss all the time (d**n GM for not Calibrating the Mass Air Flow Meter correctly). Shifting into Neutral and coasting downhill may or may not be a variable that is considered. So I believe the DIC would give False information in that situation.

Jester4736w Enthusiast

Jester4736w

Posted
Posted

I'm glad my truck doesn't have A/C... I probably would have been using it all the time, this last summer.

Also, thats some good info to have, about the A/C dehumidifiying (sp?) the air, therefore using the a/c compressor to do it. I always wondered why my little 4cyl would die down a little just because of the defrosters. But Without a a/c compressor on my truck, what is dehumidifying (sp?) the air for the defrosters now?

Silverado4x4 Senior Enthusiast

Silverado4x4

Posted
Posted

When I had my 2001 6.0 I went on a 643 mile trip,going there I got 13 mpg with the ac off windows down,coming back ran the ac all the way home got the same milage,13mpg,no ac windows down=wind drag in the cab.

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