I have noticed a marked increase in MPG since I stopped using the A/C after the hot weather broke. More than just a mile or two. I suspect the A/C system may be dragging a bit, but can't tell for sure. I have a 4.7 05 QC 2WD. K&N CAI, No other mods yet. Has anyone tracked MPG with and without A/C to determine difference in MPG? This is my first opportunity to run this truck without A/C since purchase. I have 4600 miles on it. I appreciate any feedback. If I have a problem, it always helps to have a good discussion developed before arriving at the dealer. MIZZLW

 

I was wondering where you lived so I might give you a decent answer. Arkansas--I think I spelled that right. I doubt if you are really seeing anything all that unusual for the heat and humidity in your area. Yes, the A/C will lower your MPG a little, as it is parasitic drag on the engine. Also, as the outside temp goes up, the high side (hot gas) pressure goes up. This is normal. As this pressure goes up, it will be most noticable when the engine is first started and the cab is hot, and the engine is cold, the drag becomes greater. As the engine warms, the enrichment cycle leans out, and as the cab cools down, the resulting head pressure also reduces. If you run your A/C a lot, and looking at where you live, I would too, This is the best time to keep your foot out of the throttle as much as possible if you want any kind of MPG. What can be done to help this a little, is to start off with the windows open, to ventilate the air in the cab that has built up during the day, unless of course you leave your windows open all the time, then it doesn't really matter.
The units have a very specific amount of gas they are charged with for them to run correctly, any more and they run worse, any less, and they run worse. The only real problem you might have that would be abnormal is if the compressor was going out, but fortunately, thats under warranty. The comp is also run in the defrost cycle with the heater, this is done to maintain oil lubrication on the shaft seal during winter operation. If you don't have trouble with frosting on the windows, its a good idea to run the defroster or a/c once a week for a few minutes, to help extend the life of the compressor seal. If the seal goes, the comp is basically shot.

Sorry its so long, but a/c stuff can get kind of complicated.

 

i just know that ac sips away gas at least 3-6% or so, and it takes air from the engine a lil bit so the engine tries to get more air

 

Your experience is not unusual.

Even the newest, high efficiency compressors take considerable power to run. The smaller the engine, the bigger the hit. I seriously doubt there is anything wrong with your new truck.

All the best.

 

Also, with the cooler temps you have more O2 in the air per given density which translates into more power which can equal better MPG also. You're also not running the fan, the A/C, etc. since it is cooler making the overall job that much easier for the engine.

 

Side note... the other (and I belive main) reason that the compressor is run during defrost is that it dehydrates the incoming air. This is important during defogging as opposed to defrosting cycles... it prevents humid air being sprayed on the cold glass worstening the fogging of the windows.

 

I haven't seen much of a difference with the A/C on or off. However, I do drive like an animal. That might make my first comment irrelevent.