A/C and MAX A/C

rjstaaf · Jul 15, 2004

propellerhead said:
I always thought MAX was less economical because your compressor is running 100%. It goes full blast no matter how cold it is inside the car. A/C works like the a/c in your house or apartment. When it reaches the desired temperature, it goes into 'idle' mode.

I don't know where you guys got the idea that MAX was more economical.

EDIT: I don't know which was is correct. Maybe today's a/c systems are way different from the ones from the 80s.

*shrug*

Quote from the manual of my '01 GT

"MAX A/C-Uses recirculated air to cool the vehicle. MAX A/C is noiser than NORM A/C but more economical and will cool the inside of the vehicle faster. Airflow will be from the instrument panel registers. This mode can also be used to reduce undesirable odors from entering the vehicle."

A/C-Uses outside air to cool the vehicle. It is quieter than MAX A/C but not as economical. Airflow will be from the instrument panel registers."

As someone stated earlier if your compressor is running 100% than you have a problem.

propellerhead · Jul 15, 2004

The manual for my 04 Mustang GT and my 03 Expedition EB say the same thing as your 01 GT, but I still don't see how MAX is more economical. Do they mean you'll get better gas mileage running on MAX?

Either way, I run MAX for the first few minutes until the car cools down, then switch to A/C. I've always feared an exhaust leak will make it into the car and being on MAX will not give me fresh air.

GT-03 · Jul 15, 2004

propellerhead said:
... but I still don't see how MAX is more economical. Do they mean you'll get better gas mileage running on MAX?

The regular A/C setting has to cool the outside air. For example, having to take 100 degree air and cool it all the way down to 75 degrees.

The MAX A/C setting has to only re-cool the inside air. For example, having to take 80 degree air and cool it back down to 75 degrees.

It takes more effort to cool air down 25 degrees than just 5 degrees.

CrimsonCobra_01 · Jul 15, 2004

wow, very interesting debate. glad someone knows what the hell they are talkin about

joeymatt · Jul 15, 2004

MAX does not operate the compressor at 100% duty cycle. When you switch the control to MAX AC this is all that occurs: a door, known as the Fresh air/Recirculate air door, moves in the air distribution box from a position allowing fresh air from outside the vehicle to one that allows only in-car air to move across the evaporator. The reason that the air feels cooler is because the already cooler in-car has less heat to remove (heat transfer) than that of the outside air. The only time that this is not the case is when the vehicle has been setting in the sun with windows up creating a superhot condition inside the car. In this case you will find that operating the car on regular AC will cool the car down quicker - because now the outside air is cooler than the in-vehicle air. After the air in the car has been cooled, then using MAX will once again produce the coldest air discharge.

StngStr · Jul 15, 2004

joeymatt said:
MAX does not operate the compressor at 100% duty cycle. When you switch the control to MAX AC this is all that occurs: a door, known as the Fresh air/Recirculate air door, moves in the air distribution box from a position allowing fresh air from outside the vehicle to one that allows only in-car air to move across the evaporator. The reason that the air feels cooler is because the already cooler in-car has less heat to remove (heat transfer) than that of the outside air. The only time that this is not the case is when the vehicle has been setting in the sun with windows up creating a superhot condition inside the car. In this case you will find that operating the car on regular AC will cool the car down quicker - because now the outside air is cooler than the in-vehicle air. After the air in the car has been cooled, then using MAX will once again produce the coldest air discharge.

This guy hit the nail squarely on the head. The only difference is where it sucks the air from. MAX = inside air, AC = outside air. Compressor cycles the same no matter what.

That's all.

propellerhead · Jul 15, 2004

The thing about the compressor must be old school a/c.

GT-03 · Jul 15, 2004

propellerhead said:
The thing about the compressor must be old school a/c.

If my fading memory is correct, I think that American Motors use to have a "desert" setting which did lock their compressor on.

joeymatt · Jul 15, 2004

There are many vehicles that are now equipped with systems that use a variable displacement compressor. On these vehicles the cycling clutch does not exist. The compressor displacement varies in direct relation to system pressure/ temperature.

Premium Speed · Jul 15, 2004

sorry, i was wrong about the cycle....i was thinking old GM stuff from back in my cheby days

a quote from the ford manual

"under normal weather conditions, your vehicles climate control system should be left in ANY position OTHER than Max A/c or Off when the vehicle is parked. This allows the vehicle to "breathe" through the outside air inlet duct."

why would it need to "breathe"?

StngStr · Jul 15, 2004

So mildew and odors don't build up in the system and in the car.

propellerhead · Jul 15, 2004

Premium Speed said:
"under normal weather conditions, your vehicles climate control system should be left in ANY position OTHER than Max A/c or Off when the vehicle is parked. This allows the vehicle to "breathe" through the outside air inlet duct."

why would it need to "breathe"?

I wondered about that too. I bet it's something like not rolling up your windows all the way.

Milenko · Jul 15, 2004

Premium Speed said:
sorry, i was wrong about the cycle....i was thinking old GM stuff from back in my cheby days

a quote from the ford manual

"under normal weather conditions, your vehicles climate control system should be left in ANY position OTHER than Max A/c or Off when the vehicle is parked. This allows the vehicle to "breathe" through the outside air inlet duct."

why would it need to "breathe"?

Thats pretty cool, never thought about that.

Sick thread by the way...I always had these questions but never asked

KLozeR · Jul 15, 2004

interesting...

And then is the heat radiated under the hood?

billyfe390 · Jul 15, 2004

Premium Speed said:
sorry, i was wrong about the cycle....i was thinking old GM stuff from back in my cheby days

a quote from the ford manual

"under normal weather conditions, your vehicles climate control system should be left in ANY position OTHER than Max A/c or Off when the vehicle is parked. This allows the vehicle to "breathe" through the outside air inlet duct."

why would it need to "breathe"?

When you run the AC water builds up on the evaporator and drains down out of the car. If you leave it on max the flapper closes the evap. off from the outside air thus letting mold/mildew and crap build up in the evap housing because there is no airflow to dry it off. If you ever drive a car that has a dull musty smell coming out of the vents that is why.

billyfe390 · Jul 15, 2004

KLozeR said:
interesting...

And then is the heat radiated under the hood?

What heat are you referring to.

kid_mustango02 · Jul 15, 2004

340.29m/s said:
That is the reason it sounds louder on Max A/C. Not because it is actually blowing harder, but because it is sucking in air and blowing in out using the same vents.

I ALWAYS use Max A/C.... keeps out the nasty smells from outside.

Use "a/c" to get the nasty smells from the inside outta there.....tee hee

KLozeR · Jul 16, 2004

billyfe390 said:
What heat are you referring to.

you know.. like the heat that's transfered out from your car.
I have a little AC on my window in my room and if i go outside to the rear end of the AC, there's a radiator and a little fan that blows all this heat out. Isn't that the removed heat from the air that the AC sucks in? I dunno i may be completely wrong about this

YardSpecial · Jul 16, 2004

I use MAX all the time and see no big drop in mileage.

Skirt + A/C = one cool cat !

I love a chilled cat !

CManT1914 · Jul 16, 2004

I know how to be REAL economical, don't use the A/C. I don't, and I live in Texas! Besides, I always either have my windows rolled down or my top down.

A/C and MAX A/C

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