Recirculated Air Saves Gas?

Messages
10
Location
utah
I don't know if it would make a huge difference. I suppose it would save SOME energy because the air inside the car would get cooler and cooler, and therefore not require as much new freon to be compressed, but now you're pushing the air through the A/C system more and more to get the air any cooler., instead of the open vent drawing air into it. my point? "not much"
 
Messages
4,478
Location
Southern California
Someone would have to take me by the hand and gently walk me through the "logic" that recirculating already chilled interior air* past the evaporator to maintain the desired cabin temperature is more energy inefficient than constantly bringing in HOT outside air to achieve the same comfort level. [freaknout] Think about it - do you leave your windows open in your house when you run your air conditioning on a hot day? Why would you do essentially the same thing by drawing in hot outside air in your car on a scorching day? I reject the argument that bringing in outside air to the evaporator is somehow more physically efficient than the recirculation of interior air - the blinkin' fan motor is drawing the same amperage off the alternator, regardless. *Even recirculated air contains at least a minimum amount of outside air if for no other reason that car bodies are not absolutely air-tight.
 
Messages
1,462
Location
MD
quote:
Originally posted by Ray H: Someone would have to take me by the hand and gently walk me through the "logic" that recirculating already chilled interior air* past the evaporator to maintain the desired cabin temperature is more energy inefficient than constantly bringing in HOT outside air to achieve the same comfort level. [freaknout] Think about it - do you leave your windows open in your house when you run your air conditioning on a hot day? Why would you do essentially the same thing by drawing in hot outside air in your car on a scorching day? I reject the argument that bringing in outside air to the evaporator is somehow more physically efficient than the recirculation of interior air - the blinkin' fan motor is drawing the same amperage off the alternator, regardless. *Even recirculated air contains at least a minimum amount of outside air if for no other reason that car bodies are not absolutely air-tight.
Well from time to time it helps to introduce some humidity to the system to helps the evaporator.
 
Messages
1,979
Location
Dallas, TX
Put the system on 'recirculate' after the interior begins to cool. The air passing over the evaporator won't be as hot as the air outside, therefore keeping the evaporator cooler, which will in turn cause the temperature switch to cycle the compressor less often, and for shorter durations. Yes, it's an energy saver, but only after the interior air becomes cooler than the outside air. It also maximizes the effectiveness of your cabin micro-filter, if so-equipped.
 
Messages
5,763
Location
Da Swamp
Also, possibly, less air drag (at higher speeds) if the air is flowing *around* the car? The standard advice to save gas via A/C use is to roll down your windows at speeds less than 40 mph, close them and use the A/C once the speed goes above that, to reduce drag. Of course, having the A/C on recirculate would only reduce drag by a tiny amount. Probably unnoticeable. (Heck yeah, I use it myself! I live in Da Sweatbox of the U.S.!) .
 

Kestas

Staff member
Messages
13,946
Location
The Motor City
Yes, recirculate mode will lower the demand on the air conditioning system..... not just because the incoming air is cooler, but it's drier. Alan, how does introducing humidity help the evaporator? Forcing the a/c system to squeeze humidity out of air puts a big load on the system.
 
Messages
176
Location
georgia
I think my compressor runs all the time if the air is on anyway.With my little 4 banger I can really tell if the air is on and Ive never felt the compressor kick off.
 
Messages
12,385
Location
Northern CA
quote:
Originally posted by Ray H: *Even recirculated air contains at least a minimum amount of outside air if for no other reason that car bodies are not absolutely air-tight.
I recall reading that now they delibertly include about 10% outside air for safety reasons. It used to be just leakage that let any outside air in some cars on recirculate Protection from Carbon monoxide, Blue flame special lunches, etc.
 

Kestas

Staff member
Messages
13,946
Location
The Motor City
quote:
Originally posted by Alan: Ever notice on most cars when you put on the defrost it automatically goes to outside air to remove humidity in side the vehicle?
How did you make this observation? How do you know it moved to outside air?
 
Messages
1,979
Location
Dallas, TX
Yes, outside air is used to defrost windows, but that doesn't mean it's easy on the system.... Outside air is the default on defrost in case the A/C system isn't working....in which case the interior air won't have been 'dried' before hitting the windshield, which can acutally make the fogging worse. However, removing this moisture causes more work for a functioning A/C system, not to mention the corrosion left behind when water condenses / evaporates over the years. This corrosion is what causes evaporators to fail. The drier the air, the easier it is for the A/C to cool / dry it.
 

Kestas

Staff member
Messages
13,946
Location
The Motor City
I guess it makes sense, since defrost is mostly needed in the winter. The cold outside air is usually drier than the air in the car's cabin, where people give off a lot of vapor.
 
Messages
1,483
Location
SW Indiana
quote:
Originally posted by Schmoe: Not only all that, but it also keeps the road kill funk from getting inside the cabin.
Sometimes the funk from INSIDE my cabin is worse than the road kill funk... [Wink]
 
Messages
1,483
Location
SW Indiana
I've had more than one vehicle owner's manual say, explicitly, to run the air on recirculate to save energy/fuel for this very reason.
 
Messages
1,462
Location
MD
quote:
Originally posted by Kestas: Yes, recirculate mode will lower the demand on the air conditioning system..... not just because the incoming air is cooler, but it's drier. Alan, how does introducing humidity help the evaporator? Forcing the a/c system to squeeze humidity out of air puts a big load on the system.
The evaporator works off the humidity in the air. Ever notice on most cars when you put on the defrost it automatically goes to outside air to remove humidity in side the vehicle?
 
Messages
36,417
Location
ME
Below 40'F the air runs very little to none anyway, which is when I use defrost the most in the northeast. It still bothers me to be forced to use it though. Therealdeal700, you might have a CCOT compressor, which if I had to explain it, would be a continuously variable load that doesn't quite freeze up. So when your AC has to work less the clutch stays engaged but it isn't as much of a drag. Floor the gas (most 4 bangers) and the A/C clutch cuts out for max acelleration. That, you should feel.
 
Messages
176
Location
georgia
quote:
Originally posted by eljefino: Below 40'F the air runs very little to none anyway, which is when I use defrost the most in the northeast. It still bothers me to be forced to use it though. Therealdeal700, you might have a CCOT compressor, which if I had to explain it, would be a continuously variable load that doesn't quite freeze up. So when your AC has to work less the clutch stays engaged but it isn't as much of a drag. Floor the gas (most 4 bangers) and the A/C clutch cuts out for max acelleration. That, you should feel.
Yeah my 94 s10 did disengage when the throttle was wide open but the 00 s10 I have now doesnt. Guess it has the varible thing youre talking about
 
Messages
10,843
Location
Nokesville, VA
quote:
Originally posted by Alan: The evaporator works off the humidity in the air.
I can tell you that the more humidity in the air, the less efficiently the evaporator can cool it, and the warmer the air coming out of it. When I turned on my home A/C unit for the first time this year, the air coming out of the vents really wasn't that cool. As several days passed and it got a lot of the moisture out of the house, the air coming out of the vents got noticeably colder and it cools down the house faster.
 
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