Why 2 air conditioner settings?

[unrequited]

Maybe it's common knowledge, but I have no clue so that's what brought me here. Why are there two air conditioner settings on most American made vehicles? There is A/C and A/C Max. I can tell the difference of the airflow, but why?

Thanks for any input.

[honda_racing101]

Maybe if its really hot you want more flow but if its just warm you dont want so much

[unrequited]

If it were that simple...but somehow I think there is more to it then just air flow. I was hoping someone would tell me it was a difference of stress on the engine, or that one setting recirculates the air and the other brings in fresh air from outside...or anything

[drdisque]

yes, A/C Max recirculates interior air while regular A/C brings in fresh air. They both run the Condensor at the same load.

[curtis73]

Yeah, GM did it funny. Max recycles interior air and any of the others take in outside air, like drdisque said.

For the most part, the stress on the engine is similar regardless of where its set. The main factors are ambient temperature, insulation of the car, and condenser efficiency, but the the AC will operate the compressor until the sensors tell it to stop. Those sensors are the high pressure sensor and the evaporator temp sensor. The compressor runs until the high side reaches enough pressure, or until the evaporator reaches 32 degrees. If it runs longer, the evaporator will freeze and be useless, or the pressure will exceed useful boundaries.

In general, the load is proportional to the amount of heat the system is asked to displace. If you get in your car in the walmart parking lot and put in on an outside setting, it will provide less draw than if you set it to Max since its sourcing the cooler outside air. Later, after the interior is cooler, using Max will be less of a load since you're sourcing cooler inside air.

[unrequited]

THanks guys...I sorta knew that would be the answer, but I had to ask. I just bought a 2005 Ford F-250 diesel, and even the salesperson had no clue.

Once again, thanks for putting this mystery behind me...LOL