Car air conditioner causes car to accelerate.?

Question

Whenever i put my air conditioning on in my car (2002 Chevy Cavalier) and the oil temp is above 90 and the car is in first gear, (automatic transmisson) it causes the car to accelerate. I actually have to hold the brake to keep the car from rear ending other cars. Any ideas?

Answer 1

Yep...most cars have an idle speed solenoid that is energized when the A/C is turned on. This is because typically the A/C compressor sucks energy out of the engine because it takes a lot of power to run it. So the solenoid senses when you turn on the A/C and slightly increases the idle speed of the motor to compensate for the additional drag on the engine.

Most likely your solenoid (or some component of the linkage in the solenoid system) is not adjusted correctly, as it should affect only the idle speed of the motor, not the cruising speed.

A failing IAC will also cause other situations such as a rich mixture condition (too much gas, not enough air) and this will be detected by the on-board computer and that will cause the engine light to go on. If the IAC has failed, that can also be detected by the on-board computer and show by having the light go on. You can take the car to the dealer, most parts stores, or a mechanic and have the codes read that will give you the reason that the light is going on...and probably a further clue to what component has failed!

Answer 2

This problem is due to a high idle adjustment being set wrong.

Here's how it works and exactly what is happening. The AC compressor uses the engine to operate and the amount of horsepower required to turn it can be significant compared the amount of HP generated by a slow turn engine (idle speed). In order to keep the AC from choking down and killing an idleing engine, the motor has an electronic solinoid that increase the idle speed when it detects the AC is turned on. This idle increase also happens (on some newer models or those with motors too small for car) when the Alternator senses a large draw and needs more RPT to keep up with the draw of electricty. Thus your car is asking to up the idle for the AC and since you have other electrical draws on the car (oil temp higher which forces the secondary fans on) this is where the increase in speed comes from.

This is normally a good thing and is NORMALLY only a small amount of RPM increase which is just enough to compensate for the requirements of the AC. However, I suspect in your case this High Idle adjustment is set too high and thus bringing your engine speed up more than necessary.

How to fix, well, this high idle adjustment can be in various places. But the first place to look is where the throttle linkage attaches to the air plenum (or carborators on older models) and look for where the rotating mechanism sits against an ajustable screw or solinoid. To help find it, have someone inside the car (not running) press on the gas peddle and you'll see what moves. Now, look for a point where the throttle assemble part that moves rest when the person in the car lets off the gas. What you are looking for will have an electrical wire attached to it.

Some high idle solinoids are adjustable and some are not. If it is adjustable, you should see pretty easily how to adjust. If not, you'll need to replace it. Some really new vehicles don't use the throttle adjustment but adjust things electronically. These are a bit tricker to fix... but I don't think you have this type.

Good luck and I hope this helps!

Answer 3

revered les this is a 2002 car they shouldnt do this. my girl friend has a 2001 which is the exact same car and she has never had this problem. to me honestly it sounds like you possible need a tune up because the car is idling higher. 2nd it might be the idle air control valve or the tps (throttle position sensor is becoming defective. or maybe the Maf ( mass air flow) sensor. its something going bad causing the car to idle higher than normal. on these cars this cant happen for to long because its going to make the engine light come on. if the light is already on take it to autzone and get a computer check. the later cars or made according to strict emission in certain states so you must figure out what is causing this. and try to get them to best explaination of this problem to you

Answer 4

Get the transmission checked.

The AC is not hooked up to the transmission in any way, shape or form so it can't be the total cause of the problem. It has to invlove the oil pressure as well so you need to get that checked.

Then only thing I can think of that is happening is that you are pushing extra hydraluic fluid around the transmission because the oil pressure is too high. That is the only way the two systems can link.

Answer 5

Its most likely the ac compressor clutch since when you first switch on the ac the clutch engages and you hear the noise but after you start going it stops ask your mechanic to take off the serpentine belt and turn the ac compressor pully by hand and if you hear the scraping noise while turning the pully then its the pully and if not its eaither the compressor or the clutch if the compressor is covered in dirt then you need a new compressor becasue it is leaking

Answer 6

Many A/C'd cars have a throttle-opening mechanism (usually a solenoid) that raises the idle speed slightly when the A/C comes on. Yours might be adjusted a little bit too aggressively.

Answer 7

One of the ECM's jobs is to allow the car to continue to run. When extra power is needed, it will increase rpm's just before added device kicks in. With smaller engines, like yours, until the ECM knows how much power is required, it will go a little overboard until it learns.
P.S. ECM (engine control module) is the "computer" of the car.

Answer 8

When the AC is on, the RPM's do run higher than normal. This would cause the sense of acceleration. It is normal.

Answer 9

Sounds like your ac is forcing more engine into the car then normal causing it to accelerate.

Answer 10

sum1's hooked up that dang aircon to the turbo-charger