Does turning off the AC give my car a horsepower boost?

Dear Car Talk

Dear Car Talk | Nov 01, 2001

Dear Tom and Ray:

My wife insisted that I send you this question, which is the source of an increasingly pointed argument that is close to breaking out into dripping sarcasm. We have a 1993 Toyota Corolla, and when it goes up a steep highway incline, it needs all the power it can get. As a result, when I merge onto a highway with a steep grade, and the AC is on, I will often turn it off long enough to accelerate to highway speed, then I'll turn it on again. I swear I can feel the car surge with added power when I flip off the AC switch. My wife, however, thinks this is silly. So, does turning off the AC provide an additional power boost? And will I harm the car in any way by doing that? -- Scott

RAY: Yes it does, and no you won't. It does provide a power boost, and it does not harm the car. Your wife is going to hate us for saying this, Scott, but you're absolutely, 100 percent right.

TOM: The engine provides the power to run the air conditioner. And the engine only has a finite amount of power that it can make. If you had a large V-6 or V-8 engine, you wouldn't even notice the power drain from the air conditioner.

RAY: But when you have a little engine, like the one in your Corolla (I'm assuming you didn't get the V-8 option), the air conditioner can drain enough power that you could actually feel the difference. You wouldn't notice it during normal driving, but in the most demanding conditions, you certainly could.

TOM: In fact, automotive engineers figured this out some years ago and developed a switch so the AC would be turned off automatically when the engine needed all of its power. It's done through the computer and the throttle-position switch. And it does exactly what you do, but automatically.

RAY: So I have no doubt that you feel the difference, Scott. And I have no doubt that you will also kindly refrain from dripping sarcasm when you deliver your "I told you so."

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One