Turning off a/c to avoid overheating when climbing hills

Here in California, it is not unusual to see a sign sayingj “Turn of a/c next xxx miles to avoid overheating” when climbing elevation on long stretches of highway or mountain roads. I was wondering: with modern cars, is this still necessary? And, if so, is it sufficient to just turn off the a/c and let the fan run or should even the fan be turned off? I live in the desert and sometimes, a stretch of road with this sign can go on for 15 miles in 100+ degree heat.

That’s left over from the '60s. I doubt that any modern car in decent shape would need the a/c turned off. Of course, towing (especially overloaded) would change that.

If your engine is actually overheating, it certainly doesn’t hurt to turn off the AC, not only is there less load on the engine, but you don’t have hot air from the condenser hitting the radiator.
Also, turning on the heater helps, it’s basically a second radiator.

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That’s what I figured. However, I don’t mind turning off the a/c as long as I can keep the fan running.

No, it doesn’t overheat. On the other hand, I’m always turning it off when I see the signs to be safe. Just wanted to be sure that hitting the a/c switch but leaving the fan running was still ok.

I don’t know if they still do , but for many years Chrysler products turned off the A/C when at full throttle, like pulling a long steep hill. I think they figured emergency acceleration was more important than A/C.

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I have driven 1960’s and 1970’s cars on those grades with marginal cooling systems that got hot and it was necessary to switch off the air conditioning. Even with a new radiator and fan clutch the temperature would climb in the desert heat on grades.

Switching off the A/C on vehicles built in the last two decades should not be necessary. If a late model vehicle cannot operate in normal desert temperatures there is a problem.

I sometimes switch off the A/C compressor on grade when driving my old 4 cylinder Dodge in a effort to maintain 70 MPH but there in not a cooling system problem.

Sounds like a stretch of the truth but Bakers Grade is a climb more than 15 miles long and has those warning signs.


If a vehicle overheats on a steep grade it’s due to the load on the engine at low RPM. Both heat and load can be harmful to an engine. One way to combat this is to put the transmission in a lower gear to keep the RPM’s up.

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The car is equipped with either a gauge or a light to tell you when the car is overheating. Some even turn off the AC automatically when the car starts to overheat.

Let the car do its job and don’t worry about it. Just glance at the gauge or dash every now and again like you would normally do (you DO right?) and enjoy nice cool AC.