Car jerks when I turn on A/C. Why?

When I turn on the A/C in my car, it jerks (particularly, when I am stopped at red lights). Why is this?

I just had my alternator replaced and the mechanic told me my battery tested as weak. Would replacing the battery fix the problem?

Replacing your battery won’t help.

Your A/C works by running a compressor. The compressor requires a lot of power and runs off of the motor. Your Aveo is a tiny little car with a tiny little engine. What you feel is the result of the extra load of running the compressor. If you pay attention you’ll also feel it when you drive as the compressor cycles on and off.

What year is the Aveo and how many miles? You might have someone inspect your motor mounts. Worn or broken mounts will make this feel worse. Other than that, its just the way it goes.

Thanks. It’s a 2004 with 70,000 miles on it. I’m very sensitive because I believe I bought a lemon - I’ve had it for less than 3 weeks now and I’ve had to get the front light replaced, the break pads replaced and, now, the alternator. It looks like I may need to get the battery replaced, too, as this morning the car started but, for a second, it almost died. Sigh. I live in Guam where there is technically a lemon law, but it’s not enforced.

So, is your advice not to worry about the small little jerks my car makes when running the air? I do feel it as I drive too, though usually it’s only when I’m stopped.

Yes, you should ignore the jerks though having someone check the mounts is not a bad idea.

FYI: a new battery will not help the AC situation, but a weak battery will wear down your new alternator. If you have someone you trust to check the charging system and are told that the battery is not doing well you should just replace it.

The items that you describe as a problem (brakes, lights, alternator) are pretty normal repair/maintenance. The dead alternator is a little early but not out of line. So this is not a lemon. It sounds like maybe you needed a mechanic to check it before buying. Do yourself a favor and buy a $20 repair manual for the car. You bought and older higher mileage car. Things are going to break and need maintenance. With a repair manual you can save some money on simpler things and at least be able to better understand what is going on when you have mechanics dealing with it.

The same AC compressor is likely used in several model cars, including bigger ones with more powerful motors. If you were driving a 300hp Caddy you wouldn’t feel the AC compressor kick in. With a 90 hp Aveno you are going to feel it, and you’ll notice a significant power loss on the road.

Your Aveno might be a lemon, but it is designed to be a very basic car. They won’t put special circuts and parts in a low end car to keep you from feeling an AC compressor kick on.

A car like a Mercedes will have unique ways to make the AC kick in so seemless the driver and passengers won’t feel it. You gets what you pay for. As long as you are cool, and the car doesn’t stall when the AC kicks in that’s the best you can expect.

You might want to have the Idle Air Control valve checked out. When the AC is turned on it puts a load on the engine. The IAC valve is supposed to bump the idle speed up to compensate for this extra load put on the engine. If the IAC valve fails to go to the proper position for this extra load on the engine, the engine will shake and jerk while stopped and idling.


You just may want to see if your compressor is cycling excessively (sign of a low charge)

Sometime back I owned a 1971 Ford Maverick with a 250 cubic inch 6 cylinder engine. I could always feel the AC compressor kick on and off. The engine is your Aveo probably has less power than my Maverick had, so I am not surprised that you can feel the compressor go on and off.