Switching A/C Off on hills - on ramps


Last weekend Tom and Ray stated that the car does this by itself and told the good Pastor not to do it.

I believe that the A/C does not turn off by itself while on onramps and that it is a good idea to save fuel/ lives. What say you?


Actually, what Tom & Ray stated is that the compressor drive “cuts out” when you do rapid acceleration. If you floor the gas, or at least press on the gas pedal in a very forceful manner, the compressor will, indeed, “cut out” on modern cars.

They never stated that this occurs automatically on hills or on ramps, and in fact, the “cut out” process is entirely dependent on how hard one is accelerating, not the grade that one is driving on.


Agreed with VDCdriver. The compressor cutout has actually been around for quite a while. SAAB first started using this back in the late 70s.


Some they do and some they don’t and some you just can’t tell. Some they will and some they won’t and some it’s just as well. Don’t wear the switch out and keep your attention on your driving. Don’t bend your metal by worrying about small details. The compressor isn’t always on anyway. No matter what kind of car you drive. Enjoy the trip, don’t tailgate and all that other good advice.


I almost never put the gas pedal to the floor, and honestly, barring emergency situations, I don’t believe that a good driver should have to. That said, I almost always shut off the AC when I need to pass or go on an onramp, not so much for fuel economy, but to have more power at lower RPMs. I drive a small car, and it feels like the AC sucks about half the engine’s power. Turning it off briefly makes very little difference in the car’s temperature, but it makes a big difference in how easily I’m able to drive my car safely.


I’ve noticed on commercial air flights that the lights are turned off in the cabin during take-off. When the plane reaches altitude, the lights are then turned back on. I assume that this is done to take unnecessary load off the engine turning the generator during take-off and that the co-pilot probably does this. The good pastor should assign his wife the responsibility of turning off the air-conditioner when ascending an interstate ramp. If he would make his wife part of the driving team, she might not argue about whether or not the air conditioning needs to be turned off under these conditions. Furthermore, when she is driving, he would assume the responsibility of turning off and on the air conditioning, and he might decide that this really isn’t necessary.


He may have had a good point in the past. I remember as a kid going to Boy Scout camp with myself and my friend in the back seat, his older brother in the front seat and his Dad driving. The back of the wagon was loaded with camping gear, and it was pulling a trailer, also loaded with camping gear. This was something on the order of a 1980 Escort Wagon, faux-wood paneling on the sides. Anyway, we had to travel on several highways to get to the camp, and it was a hot summer trip. The A/C was on, but the older brother in the front seat was assigned the task of pulling the A/C lever all the way to off whenever hill climbing or merging or acceleration were called for. Invariably, he’d forget, the car would max out at about 40 on the acceleration, cars would swerve to avoid missing us, the Dad would holler, the kid would panic and pull the wrong lever, we’d be cracking up in the back seat, thereby causing more hollering and general hilarity. Anyway, when the A/C was finally switched off, the car accelerated to a speed at which it was possible for us to continue to live on said highways. Once up to speed, the A/C went back on. So, this probably doesn’t apply to a modern car that doesn’t suck, but there’s probably some truth/history to the story.


Lights are turned off during takeoff and landing in airline cabins to make readouts, gages, HSI indicators, and especially warning lights more visable and noticable. Takeoffs and landings are by far the most critical parts of a flight, and as a pilot you don’t want to miss anything. Once you’re straight and level with your automatic flight control systems engaged then you can turn the lights back on and spill your coffee everywhere.


The door, though, is closed to the cockpit where the gauges are, so I can’t see that having the lights on or off in the cabin would make a difference in reading the instruments. On landing, where I think they would also have to watch the instruments, they leave the cabin lights on.


The AC may or may not turn off automatically during full throttle acceleration.

If the vehicle is an overloaded, gutless wonder, every little bit of power is important. If you can notice the effect of switching off the AC, it is worth doing until you are up to speed.

My first generation Mazda RX-7 is neither overloaded nor gutless, but with only 135 hp, briefly switching off the AC does noticeably improve acceleration.

If you have a powerful car (at least 250 hp), you won’t be able to tell whether the AC is on or off.

Any fuel savings due to shutting off the AC have nothing to do with hills or on ramps. The AC draws a few horsepower and it takes fuel to produce that power whenever the AC runs.


Some vehicles do have limiter switches which basically shut off the AC when you mash your foot to the floor (of course, I’ve never had this happen to me). As far as shutting off the AC while on hills or ramps, you will save almost nothing in the way of decreased energy usage, and what you do save you will shell out in the form of additional wear and shortenend lifespan of your air conditioning compressor. If you want to find out how much you would really save, drive the same course at the same speeds while switching off the AC on ramps and hills, and the while leaving AC on. I predict you won’t be able to see a difference. Of course, I’m in Florida, so what the heck do I know?


negative good buddy, wrong on all counts.

the lighting load in the cabin is but a small part of the electrical load. pumps, valves, motors, entertainment systems, galley equipment comprise a much larger portion of the load.

the FA (flight attendant) turns the cabin flood lights on and off. lights on or off is a function of each airline’s operations philosophy (some airlines require the window shade be open for takeoff and landings, others don’t care) and is published in the cabin attendants SOP’s (standard operating procedure).


I think people should not worry about the A/C and focus on what is important. Things such as talking on the cell phone, putting on make-up, watching DVD’s are all far more important than worrying about whether or not you can safely accelerate onto a highway.

Gotta go. Incoming call…

Robert (written while driving, shaving and typing with one hand)


I’ve got a 2002 Toyota Echo-- compact, economy car that nevertheless usually has adequate power on hills, passing, etc. The A/C definitely does NOT cut out with the accelerator floored on this car. There is a significant hill near I live, and I frequently drive up it (I have to go over it to get to the casino). Normally, with the A/C turned off, I can go up this hill at speed. After hearing the comment on Car Talk, I tried driving this hill with the A/C turned on. I found that I started losing speed near the top of the hill, even though I had the accelerator floored. When I turned off the A/C, my speed stabilized and increased. Is it possible that they only put this cutoff feature in cars that are a bit beyond the bottom of the economy price range?