Based on Discovery Channel they once carried out analysis to determine wether cars with AC on consumes more fuel. The presentation based on this, they
used the same type of vehicles one
with AC on the other off to cover
the same area of distance, the
result will astonish you, the one
with AC actually consumes less
fuel, you may doubt this theory,
but it's simple to find the answer,
the belief that driving with AC
consumes more fuel was based on
the time that most vehicles in
Nigeria came without AC, and the
people locally installed AC in them,
all modern cars now come with
factory fitted that has no
significant impact on the fuel,
conclusion:, if you are traveling on
a long distance journey for
example it is ideal to drive with AC
on to save fuel and also to maintain
balance gain more traction, if you
are driving on a high speed without
AC and Windows down your motor
would need more tug to break the
dragging of the wind thereby
consuming more fuel. Don't mind

I doubted this at first...But the explanation on drag reduction makes sense out of it all.

Interesting! Who else can prove this.

Whereas on modern cars as you mentioned the first thing the ECM will shut down when there is a problem is the AC due to the additional load of driving the compressor. If what you are saying is right, then what is the reason for the load shedding?
Additional, I don't think it is possible for two people to drive alike and even for the same person to repeat the same scenario twice. Take another look at it.

Based on personal experience AC dey consume fuel. Meanwhile that drag according to another study only makes ac a better option while driving over speeds of 40mph on lesser speeds, SC consumes more fuel than said drag effect

High fuel consumption or not, I shall always put on my AC

Depends on your speed. At higher speed, the drag generated by having your windows open offsets the lack of AC.

In any case, AC does affect fuel economy. Don't be deceived.

Like the man above, though, my AC is always on, causes das how star do. Best way to use AC is with temperature and fan on lowest.

I don't want to know how it feels driving without ac or how much fuel i will save .

@Op You got the essence of the experiment wrong and I think you will need to edit the topic of this thread not to mislead the general public.
The essence of this experiment is to show that a car that has its window open even without ac on when speeding at higher speed around 100 km/hr will consume more fuel than another car that it window is closed even with the AC kept on .
What they actually want to prove is that dragging force that enter a car when the windows are opened is very substantial and even greater than when you close the window even with ac load when traveling at high speed .
To set the record straight ,Any load on the car whatsoever eg ac compressor and basic accessories like lights ,power steering ,wiper etc when turn on will increase the fuel consumption of car and the consumption will depend on the current the load is consuming .
So traveling at high speed with ac will always consume more fuel than when ac is not on so far the windows are close for both instance .
Lot of technology breakthrough has been introduced to reduce ac load by introduction of VDC compressor and dedicated ac module just to reduce the load of ac compressor but it impossible to achieve zero load with ac cos of law of conservation of energy.
Finally , let me add to this piece by stating that reducing the temperature of ac and blower fan speed just to save fuel will only be effective when dealing with the VDC type ( automatic ) of compressor system but is not significant when u are dealing with the FDC compressor (manual compressor )

Then why does ECO mode reduce the AC performance. At least it does in my vehicle and the manual advises you deactivate eco mode if the AC isn’t cooling enough.

For the compressor belt to be tugged by the engine means it’s extra load.

Toyn:
Whereas on modern cars as you mentioned the first thing the ECM will shut down when there is a problem is the AC due to the additional load of driving the compressor. If what you are saying is right, then what is the reason for the load shedding?
Additional, I don't think it is possible for two people to drive alike and even for the same person to repeat the same scenario twice. Take another look at it.

Are you sure of that? The only link i know is increasing or decreasing RPM due to the AC load but not shut down.

I quite agree that highway driving with ac especially at high speed will save you some fuel but at slow speed such as city driving, you will use more fuel.

Namzy:
Based on personal experience AC dey consume fuel. Meanwhile that drag according to another study only makes ac a better option while driving over speeds of 40mph on lesser speeds, SC consumes more fuel than said drag effect

You are seriously underestimating air drag. F1 cars dont look the way they do for fun. Put the same engine in a saloon and an SUV, even if both have the same power to weight ratio, the SUV will consume more fuel due to aero-dynamic drag.

I have noticed I use same fuel on highway with ac or not. It is city driving with ac that consumes fuel and thats when air drag is minimum and friction higher.

A good example is when your car is running hot. Most modern car will deactivate your AC to reduce the load on the engine, otherwise the engine will de- rate.

autologic:
@Op You got the essence of the experiment wrong and I think you will need to edit the topic of this thread not to mislead the general public.
The essence of this experiment is to show that a car that has its window open even without ac on when speeding at higher speed around 100 km/hr will consume more fuel than another car that it window is closed even with the AC kept on .
What they actually want to prove is that dragging force that enter a car when the windows are opened is very substantial and even greater than when you close the window even with ac load when traveling at high speed .
To set the record straight ,Any load on the car whatsoever eg ac compressor and basic accessories like lights ,power steering ,wiper etc when turn on will increase the fuel consumption of car and the consumption will depend on the current the load is consuming .
So traveling at high speed with ac will always consume more fuel than when ac is not on so far the windows are close for both instance .
Lot of technology breakthrough has been introduced to reduce ac load by introduction of VDC compressor and dedicated ac module just to reduce the load of ac compressor but it impossible to achieve zero load with ac cos of law of conservation of energy.
Finally , let me add to this piece by stating that reducing the temperature of ac and blower fan speed just to save fuel will only be effective when dealing with the VDC type ( automatic ) of compressor system but is not significant when u are dealing with the FDC compressor (manual compressor )

The fan blower level has control over the compressor ON time. For example (hypothetically), if fan is put at level 1, when compressor clutch engages for 30 secs it goes OFF for 10secs and continue to toggle at the same rate. But when you increase blower level to 2 it also increases the clutch engaged time say 40secs ON and 10secs OFF. At level 3 you get say 60 secs ON and 10 secs OFF then at final level you get say 90secs ON and 10 secs OFF. Some cars come with MAX AC button, this is the bypass button to the clutch and keeps the AC clutch engage full time unless there is too pressure in the system then the pressure switch stops the ac system completely till normal pressure is achieved. In that case, most ac ON lights will blink to show system problem.

Therefore, the fan lower level will also determine fuel consumption since it controls how long the ac clutch remains engaged.

Lastly, i think the message op is trying to pass is that driving at high speed using ac which means winding up will balance out or even be more economical to air drag when you drive without ac and your windows down in terms of fuel consumption. I have compared this severally and it works. You will use roughly the same fuel in the 2 instances.

adanny01:


The fan blower level has control over the compressor ON time. For example (hypothetically), if fan is put at level 1, when compressor clutch engages for 30 secs it goes OFF for 10secs and continue to toggle at the same rate. But when you increase blower level to 2 it also increases the clutch engaged time say 40secs ON and 10secs OFF. At level 3 you get say 60 secs ON and 10 secs OFF then at final level you get say 90secs ON and 10 secs OFF. Some cars come with MAX AC button, this is the bypass button to the clutch and keeps the AC clutch engage full time unless there is too pressure in the system then the pressure switch stops the ac system completely till normal pressure is achieved. In that case, most ac ON lights will blink to show system problem.

Therefore, the fan lower level will also determine fuel consumption since it controls how long the ac clutch remains engaged.

Lastly, i think the message op is trying to pass is that driving at high speed using ac which means winding up will balance out or even be more economical to air drag when you drive without ac and your windows down in terms of fuel consumption. I have compared this severally and it works. You will use roughly the same fuel in the 2 instances.

Let me make some clarification to your statement about the relationship between the fan blower speed and the compressor turn on time .
1. For the AC design you are referring to , The AC control module uses the input evaporator temperature sensor signal to determine the cut -off time of the compressor .The cut off time of compressor is not based on certain arbitrary time as you assume but based on set evaporator temperature .That is when the blower fan is increased to higher level ,the AC module will set the evaporator temperature that the compressor will cut off lower and vice versa .
2.The FDC compressor working as opposed to the VDC is 100% that it is putting all it %100 full capacity to the pumping of refrigerant.Hence some infrequent cut off it experiences when the evaporator set temperature is reached occurs for few seconds and will not be significant enough to use that as saving fuel grace as u assume .
This is why manufacturer came up with design of the VDC compressor to give a better mileage as the pumping capacity of the compressor can be varying from %1-%100 based on alot of set algorithms which is based my user "needs" instead of the ancient old FDC technology that can never reduce it working capacity other than cut off for few seconds which doesn't make any significant contribution to fuel mileage.
3. Then finally talking about the message the op is trying to pass across ,check the topic of this thread ,I feel he should edit it to pass clearer message across cos the subject of the topic is misleading and erroneous .
Better topic should have read like this " You save more fuel when you wind down your window "
The essence of the experiment is actually on the effect of air drag on fuel ,the use of ac is just a control aspect of the experiment not the subject .

Running any air conditioning that involves driving a compressor off of the crankshaft absolutely decreases MPG. Fact.

This is why aftermarket has gone in search of battery powered water pump and cycling alternators.

Sure, you can dance with rolling windows down or up and freeway out city driving but ultimately AC decreases MPG.

This is not directed at the OP as he will believe what he wants but my post is directed to someone with an open mind that really wants to learn.

autologic:

Let me make some clarification to your statement about the relationship between the fan blower speed and the compressor turn on time .
1. For the AC design you are referring to , The AC control module uses the input evaporator temperature sensor signal to determine the cut -off time of the compressor .The cut off time of compressor is not based on certain arbitrary time as you assume but based on set evaporator temperature .That is when the blower fan is increased to higher level ,the AC module will set the evaporator temperature that the compressor will cut off lower and vice versa .
2.The FDC compressor working as opposed to the VDC is 100% that it is putting all it %100 full capacity to the pumping of refrigerant.Hence some infrequent cut off it experiences when the evaporator set temperature is reached occurs for few seconds and will not be significant enough to use that as saving fuel grace as u assume .
This is why manufacturer came up with design of the VDC compressor to give a better mileage as the pumping capacity of the compressor can be varying from %1-%100 based on alot of set algorithms which is based my user "needs" instead of the ancient old FDC technology that can never reduce it working capacity other than cut off for few seconds which doesn't make any significant contribution to fuel mileage.
3. Then finally talking about the message the op is trying to pass across ,check the topic of this thread ,I feel he should edit it to pass clearer message across cos the subject of the topic is misleading and erroneous .
Better topic should have read like this " You save more fuel when you wind down your window "
The essence of the experiment is actually on the effect of air drag on fuel ,the use of ac is just a control aspect of the experiment not the subject .

Well spoken. Alot of people really need to understand what exactly is going on. Understanding the system, its design and how it works is paramount to knowing what exactly is going on. People just come uo with theories without knowing how the system works.

Well said.

autologic:

Let me make some clarification to your statement about the relationship between the fan blower speed and the compressor turn on time .
1. For the AC design you are referring to , The AC control module uses the input evaporator temperature sensor signal to determine the cut -off time of the compressor .The cut off time of compressor is not based on certain arbitrary time as you assume but based on set evaporator temperature .That is when the blower fan is increased to higher level ,the AC module will set the evaporator temperature that the compressor will cut off lower and vice versa .
2.The FDC compressor working as opposed to the VDC is 100% that it is putting all it %100 full capacity to the pumping of refrigerant.Hence some infrequent cut off it experiences when the evaporator set temperature is reached occurs for few seconds and will not be significant enough to use that as saving fuel grace as u assume .
This is why manufacturer came up with design of the VDC compressor to give a better mileage as the pumping capacity of the compressor can be varying from %1-%100 based on alot of set algorithms which is based my user "needs" instead of the ancient old FDC technology that can never reduce it working capacity other than cut off for few seconds which doesn't make any significant contribution to fuel mileage.
3. Then finally talking about the message the op is trying to pass across ,check the topic of this thread ,I feel he should edit it to pass clearer message across cos the subject of the topic is misleading and erroneous .
Better topic should have read like this " You save more fuel when you wind down your window "
The essence of the experiment is actually on the effect of air drag on fuel ,the use of ac is just a control aspect of the experiment not the subject .

Well said.

Thats why i said hypothetically. I also agree that the fuel saved by cutting off the compressor for small time is insignificant and will not in the overall appear as fuel saved.

UnitedAlliance:
Running any air conditioning that involves driving a compressor off of the crankshaft absolutely decreases MPG. Fact.

This is why aftermarket has gone in search of battery powered water pump and cycling alternators.

Sure, you can dance with rolling windows down or up and freeway out city driving but ultimately AC decreases MPG.

This is not directed at the OP as he will believe what he wants but my post is directed to someone with an open mind that really wants to learn.

We are all learning day by day. The op should see it as an opportunity to have the issue discussed in detail bringing more knowledge to the thread. We all benefit one way or another.

However, we all agree that AC is an extra accessory and will take out some power off the engine leading to a little more fuel consumption. The message is that if you travel at 120km/h with windows down, you experience drag that you will not see but it exist. That drag if hypothetically consumes 5hp from your engine, you will still maintain the same fuel efficiency if you close the window and put AC which by the same hypothetical measure consumes 5hp from the engine. It is just give and take but ultimately, the engine power will be taken one way or another which should result in more fuel.

The only issue is that we cannot proof that the drag of open window no ac is equal to closed window with ac. The only thing we know for certain is that the relationship exist.

Personally, if i am traveling light on highway, my experience with my car is that AC or no AC i use the same fuel. I have tried it countless times and it works but that is not true for city driving. AC will definitely lead to decrease in mpg.

Let me add by saying, a lot of Nigerians driving on highway with perfect ac system but are too fuel conscious to be in the comfort of the AC. This is a good attempt to let them understand that even if there is going to be more consumption, it wont be more than a litre or 2 (N150-300) for most short journeys or 200-300km.

Nice summary, adanny01

Sometimes, the savings in economy comes from timely trade-offs. Using the directional A/C vent when it rains, even in city driving, improves visibility and safety. Keeping the windows up in city driving carries beyond comfort to security, safety and visibility.
Personally, it helps me deduce the state of the engine. I hear the compressor and the fans kick-in and go off, I watch my temperature gauge more closely and tune my sense of smell. I have come a long way, with experiences that necessitated those. It becomes an advantage during interstate driving because you trust the car and become more confident...with a very safe arrival

HeavenlyBang:
Depends on your speed. At higher speed, the drag generated by having your windows open offsets the lack of AC.

In any case, AC does affect fuel economy. Don't be deceived.

Like the man above, though, my AC is always on, causes das how star do. Best way to use AC is with temperature and fan on lowest.

Speed matters bro, at higher speeds of about 60mph driving with ac on is more economical than Windows down due to drag but at speed less than 60mph windows down is the way to go if u wanto save some bucks on fuel.