Question: Does warmer AC = lower fuel comsumption?

[Nicolas Dore]

Hello

I have had a 2000 Legacy wagon for 2 months now and it is my first car
with AC. Which led me to wonder... : Using the AC uses gas (compressed
"freon" - not freon, whatever replaced it and is ozone-friendly -
takes heat away from air, compressor compresses "freon", takes energy,
engine has to work more...). If I put the heat dial, let's say, half
way down the blue/cold side, am I using half as much gas for the AC
(compressed gas takes less heat away from air, compressor compresses
"freon" less to get less cool air, engine has to work less...) or not
(compressed gas takes just as much heat away from air, compressor
compresses "freon" just as much, takes energy, then air is re-heated,
so engine has to work as much...)?

Very important stuff...

Thanks in advance

Nicolas

 

[Victor Roberts]

Hello

I have had a 2000 Legacy wagon for 2 months now and it is my first car
with AC. Which led me to wonder... : Using the AC uses gas (compressed
"freon" - not freon, whatever replaced it and is ozone-friendly -
takes heat away from air, compressor compresses "freon", takes energy,
engine has to work more...). If I put the heat dial, let's say, half
way down the blue/cold side, am I using half as much gas for the AC
(compressed gas takes less heat away from air, compressor compresses
"freon" less to get less cool air, engine has to work less...) or not
(compressed gas takes just as much heat away from air, compressor
compresses "freon" just as much, takes energy, then air is re-heated,
so engine has to work as much...)?

Very important stuff...

Thanks in advance

Nicolas

No. the AC works at full capacity and then the cold air is reheated by
the heater core.

In cars that have climate control the AC may actually cycle on and off
to maintain temperature, but that is not the way the AC works, at
least in my '97 OBW.

 

[John A. Mason]

Virtually all automotive A/C units will cycle their compressors to both save
fuel (i.e. become more fuel efficient) and to prevent the system from
freezing.
You can hear, and watch, this happening. I believe that setting the
temperature higher will perhaps allow the A/C compressor to be off longer
than on, potentially saving fuel.
John

 

[Victor Roberts]

To possibly get better fuel mileage, I often keep the AC is the recirc
mode and manually turn the AC on and off when needed. I also turn
both AC and recirc off 5 minites before I reach my destination to help
remove some of the moisture from the system. This helps keep mildew
and mold down.

It is dangerous to drive for any extended period of time in air
recirculating mode. You could die from CO poisoning. The mode should
only be used for initial cool down or when traveling through a very
dusty area.

 

[Victor Roberts]

Virtually all automotive A/C units will cycle their compressors to both save
fuel (i.e. become more fuel efficient) and to prevent the system from
freezing.
You can hear, and watch, this happening. I believe that setting the
temperature higher will perhaps allow the A/C compressor to be off longer
than on, potentially saving fuel.

You are correct that the AC compressor cycles on and off to prevent
the evaporator core from freezing. However, on cars without "climate
control" I have never seen any evidence that the setting of the
temperature control has any effect on the operating of the AC unit.

 

[null_pointer]

It is dangerous to drive for any extended period of time in air
recirculating mode. You could die from CO poisoning. The mode should
only be used for initial cool down or when traveling through a very
dusty area.

....and whenever I'm approaching the rear end of a Diesel car or truck.
Yeah....I usually either open a window or take it off recirc for a
minute or so if I'm going long distance...I just didn't get that
detailed in my original post.

 

[Richard Gary Clark]

I think people are right in saying that changing your air temp setting will
not reduce fuel consumption, as the AC cools the air and then heats it back
up. But if you reduce the fan speed, you pass less air over the evaporator
and therfore it stays colder longer so the compressor will run less to keep
it cool, therfore saving fuel ?

 

[Victor Roberts]

I think people are right in saying that changing your air temp setting will
not reduce fuel consumption, as the AC cools the air and then heats it back
up. But if you reduce the fan speed, you pass less air over the evaporator
and therfore it stays colder longer so the compressor will run less to keep
it cool, therfore saving fuel ?

That does make sense.

 

[Victor Roberts]

]
You are correct that the AC compressor cycles on and off

How do I check if the compressor is running?

You can open the hood and look at it. It is easy to see when the
compressor clutch engages.

 

[Dan Duncan]

How do I check if the compressor is running?

You should be able to feel it kicking on and off.

-DanD