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Max AC simply means highest fan speed, coldest temp, and recirculation.
The compressor is on all the time until you shut down the AC. It doesn't care what fan speed you're running. That's just adding extra noise in the cabin. Recirc will recycle the air.
After the cabin temp is comfortable, the compressor will stay on and work just as hard as it did when it was 200 degrees in the cabin.
At that point there isn't much point in keeping the recirc function on unless it always stinks outside, you're low on refrigerant, or your car is insulated like a beer can.
Mpg is only affected if it's off vs on. Fan speed and recirc does not affect mpg.
I've noticed some modern cars shut off the AC while you start the car to save wear on the starter ( the starter isn't turning the AC compressor). Once the engine is on, the AC comes back on. That's genius.
I am sorry but much of what you claim is completely wrong.
Under many climate conditions the AC compressor will cycle. Particularly with only moderately hot temperatures or at a lower blower speed. If it didn't cycle off the evaporator core could ice up. In fact, this can happen when a thermostatic probe in the evaporator core fails and doesn't shut off the compressor below a certain evaporator core temperature. Most any automotive tech is familiar with the complaint that there is a clicking under the hood and a subtle tug and release on the engine using the defroster in mild weather -- say 45-50* This is normal behavior because the compressor is engaged to dehumidify the air directed to the windshield before it goes through the heater core, but because of mild temperatures the compressor keeps cycling off.
And another correction, MPG IS effected by how hard the compressor works which IS effected by fan speed and outside air vs. recirculate. Any automotive tech who has watched his/her services gauges knows this. Once a car has cooled down through recirculate mode the gauge readings drop noticeably. Less head pressure means the compressor does not work as hard.
Hmm. Never noticed the AC go to Max when I use the recirc button, only when I use the Max button. Recirc only changes where the air comes form , not how hard the AC is running in normal use. At least on my Suburban and my BMW.
¯\_(ツ)_/¯
You are correct and that is refreshing because this thread is full of misinformation!
It's $15 a year. You can't smell a clogged filter until its already in the core. Mine has sand, leaves and pollen leaves in it after 6 months. I don't smell any of that because it's on the other side of the filter. In either case the fan is working harder and your AC is less efficient.
You entirely missed the fact that I put on considerably fewer miles per year than "average." The filter is unaffected when the vehicle is sitting parked. Filters don't become corroded or lose effectiveness just because time passes. It is the forcing of air through it when driving that causes them to become used up.
YOUR filters cost $15; mine are more than twice that, and they are a PITA to replace. My replacement schedule works fine for the number of miles I drive AND for this dry climate.
I don't get leaves in mine. Why so much big debris in yours? Are you confusing the ENGINE air filter with the cabin microfilter? I change the engine air filter about once a year, varying a bit based on visual inspection of dirtiness. The cabin filter just doesn't need it as often.
You entirely missed the fact that I put on considerably fewer miles per year than "average." The filter is unaffected when the vehicle is sitting parked. Filters don't become corroded or lose effectiveness just because time passes. It is the forcing of air through it when driving that causes them to become used up.
YOUR filters cost $15; mine are more than twice that, and they are a PITA to replace. My replacement schedule works fine for the number of miles I drive AND for this dry climate.
I don't get leaves in mine. Why so much big debris in yours? Are you confusing the ENGINE air filter with the cabin microfilter? I change the engine air filter about once a year, varying a bit based on visual inspection of dirtiness. The cabin filter just doesn't need it as often.
The cabin filter is typically mileage based. I don't know why a manual would tell you to pull it on a yearly schedule.
Mine have all been easy to get to. I get leaves in mine because the outside air vent is just below the windshield. On my schedule it's actually half as often as an engine filter change. The dealer charges like $50, but I get my filters on Amazon for $15 and install them myself with no tools in about 5 minutes. For me this happens a little over once a year.
I am sorry but much of what you claim is completely wrong.
Under many climate conditions the AC compressor will cycle. Particularly with only moderately hot temperatures or at a lower blower speed. If it didn't cycle off the evaporator core could ice up. In fact, this can happen when a thermostatic probe in the evaporator core fails and doesn't shut off the compressor below a certain evaporator core temperature. Most any automotive tech is familiar with the complaint that there is a clicking under the hood and a subtle tug and release on the engine using the defroster in mild weather -- say 45-50* This is normal behavior because the compressor is engaged to dehumidify the air directed to the windshield before it goes through the heater core, but because of mild temperatures the compressor keeps cycling off.
And another correction, MPG IS effected by how hard the compressor works which IS effected by fan speed and outside air vs. recirculate. Any automotive tech who has watched his/her services gauges knows this. Once a car has cooled down through recirculate mode the gauge readings drop noticeably. Less head pressure means the compressor does not work as hard.
Don in Austin
I remember my Explorer's compressor cycling on and off frequently when it was low on freon. When I charged it the compressor would engage and stay engaged much longer. It might cycle on and off to prevent icing, but if I actually push the AC button off, it gets hot quick, so there isnt much time between the compressor being off and the cabin getting warm. My real world gas mileage on that truck was pegged at 20mpgs regardless i how I drove it or what setting the AC was on. Maybe at a theoretical level, using cooler air to cool the core would make the compressor work less, but in reality it's negligible. In auto, uses outside air. If it made the fuel efficiency go up using recirc, the AC would default to that to increase advertised mpgs and meet CAFE standards.
Only if the car is populated by really heavy breathers!
Don in Austin
This is right out of my owner's manual..
"The recirculated-air mode should not be
used over an extended period of time; otherwise, the air quality in the passenger compartment will deteriorate continuously.<"
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