Climate control question

[pirates life]

Does anyone know how the climate control on the premium adjusts temp? For example, I'm cruising on the highway in 80 degree weather, and I set the a/c temp to 70. Does the car turn off the compressor more frequently than if I had the temp set to LO, or does it modulate the temp by pumping more hot air from the engine?
My question is aimed at maximizing MPG, as I do a lot of highway driving. If raising the temp does not reduce compressor use, then using the temp seems a little inefficient, as opposed to keeping the temp on LO and turning the A/C on/off every 5-10 minutes or so.
The difference is probably negligible anyway, so just more curious than anything.

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[kn7671]

Does anyone know how the climate control on the premium adjusts temp? For example, I'm cruising on the highway in 80 degree weather, and I set the a/c temp to 70. Does the car turn off the compressor more frequently than if I had the temp set to LO, or does it modulate the temp by pumping more hot air from the engine?
My question is aimed at maximizing MPG, as I do a lot of highway driving. If raising the temp does not reduce compressor use, then using the temp seems a little inefficient, as opposed to keeping the temp on LO and turning the A/C on/off every 5-10 minutes or so.
The difference is probably negligible anyway, so just more curious than anything.

That's a good question, but I doubt very seriously that Ford designed the system to intelligently adjust temperature for improved fuel mileage by minimizing cycle time, and instead simply use the cold/hot air blend to reach and maintain the desired temp.

I'm sure some engineer at Ford has been tasked at some point to evaluate the fuel savings from an intelligent cycling a run-time of the compressor, but probably found that equipping the small percentage of vehicles that come with Auto Climate Control outweigh the savings on mileage vs losing sales from cars priced higher than the competition.

 

[jasonstang]

First of all, your compressor can change output. So it can adjust how cold the air needs to be and maintain that temperature at the evaporator. That temperature usually is a set temperature.
However, to fill in the gap in-between, hot air will be blend into the cold air if the ambient temperature is within certain degrees higher or lower than the cabin temperature.
The compressor will be turned on less frequently if the evaporator warms up slower because the climate control is blending hot air.
At highway speed, your compressor uses so little power from the engine you will almost not notice any difference in fuel economy.
Some people try saving gas driving windows down at 35mph+ they might as well just use the AC because the added resistance is about as much as AC draw.

 

[ibinubu12]

First of all, your compressor can change output. So it can adjust how cold the air needs to be and maintain that temperature at the evaporator. That temperature usually is a set temperature.
However, to fill in the gap in-between, hot air will be blend into the cold air if the ambient temperature is within certain degrees higher or lower than the cabin temperature.
The compressor will be turned on less frequently if the evaporator warms up slower because the climate control is blending hot air.
At highway speed, your compressor uses so little power from the engine you will almost not notice any difference in fuel economy.
Some people try saving gas driving windows down at 35mph+ they might as well just use the AC because the added resistance is about as much as AC draw.

Only I4 engines have variable compressors. V6 and V8 engines have fixed displacement compressors.

100% of airflow through the HVAC passes through the evaporator, and then the blend door controls what percentage of that air is then reheated. Therefore, evaporator load is dependent on HVAC inlet temperature, blower speed, and blend door position only in the sense that airflow through the hot path increase the pressure drop between the evaporator and the outlet, decreasing overall system airflow.

 

[Fleeger]

Ac usage does affect mpgs. Not to a great degree but it can be half an mpg or more. If you hypermiler at all it makes a bigger difference.

 

[Fleeger]

Where it doesn't really make a difference is when your driving around 75 mph and above since the car is already at a high load.

 

[pirates life]

Wow, pretty informative guys. Thanks.
So it seems, especially since I have a GT, which does not have a variable compressor, using the temp is a little inefficient, as apposed to manually cycling the A/c. At highway speeds the difference may be barely noticeable. Pretty much what I had thought.

 

[Qwkynuf]

Wow, pretty informative guys. Thanks.
So it seems, especially since I have a GT, which does not have a variable compressor, using the temp is a little inefficient, as apposed to manually cycling the A/c. At highway speeds the difference may be barely noticeable. Pretty much what I had thought.

The most efficient way to use your A/C is to turn on Recirculate mode. Since the compressor runs when the pressure drops due to warm air from outside (typically) passing across the evaporator, feeding already cooled air from inside the cabin to the evaporator will delay the pressure drop and cause the compressor to run less often.

It takes less energy to cool air which is already cool.

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