I noticed at stop lights when I have the a/c on sometimes my car will vibrate and rattle various things in my car. It's a pretty significant vibration. Then I turn it off and voila car is smooth again. A/c blows cold no problem with that, so any idea what it might be causing such a vibration or is this just how 4 bangers are and i'll have to get used to(last car was a v8)?

 

My car did that, but I thought it was normal? Then again, it wasn't too much of a vibration. I think it's due to the cooling fans turning on and off since the car is just idling at the light or a stop? I'm not so sure on that.

 

Look under the hood while it's idling, try to see what's doing it.

You could watch the AC compressor & wait for it to engage it's clutch. Look for pulleys that wobble (including crankshaft pulley). Or maybe even worn belts or loose brackets that allow something to flex.

Turn off the AC & jumper the fan switch (thermostat housing). That should make the fans run without the AC compressor. That can tell you whether the vibration is coming from the fan instead of the compressor.

 

Ok watched it during idle. Whenever the fans by the radiator would kick in the car would vibrate. Then they turn off and car isn't rough anymore etc. I noticed that seconds before the fans turn on that the intake seems to suck more air. Sorry if this sounds stupid, but where exactly is there a/c compressor? Passenger side right by my air intake?

 

Mine vibrates a little but it is not that pronounced. I can tell mine is just from the compressor kicking on.
I also used to drive a V8. It seems to me like the A/C robs so much power from this little I4!
I'm at work right now so I can't get outside to look at where the compressor is under my hood. (Right now all I can think about is where the one is on my wife's V6cause I justre-charged the a/c a few weeks ago.) When I get home tonight I'll check under the hoodand let you know where it is and what it looks like. Mine's a '00 LX I4 so it'll be the same as yours.

 

Leftside, low elevation. There's 3 belt-driven accessories over on the left-front of the engine compartment (left when viewed from drivers seat).

Top one is the power steering pump, driven by it's own belt.
Middle is alternator, shares a belt with AC compressor.

Bottom one is AC compressor, in the picture is has a funny triangle-shaped hub on it's pulley. When idling, you'll see the pulley/clutch engage & disengage as the AC cycles.

 

The IACV will open some pre-set amount, anticipating the load of the compressor engaging. That's avery short timebefore the compressor actuallyengages. That's probably what you hear. Possibly the compressor engages a second before the fan. The ECU coordinates all this stuff so it happens in some proper sequence.

 

Ok cool. I'm about to do an oil change so I'll be out by my car. What exactly should I look for when I watch the air compressor? Does it sound like I have a problem or is this just how these are and takes some getting use to? Thanks so much JimBlake

 

Watch the AC/alternator drive belt to see whether it gets wobbly or whether ANYTHING in particular vibrates when the AC clutches in. Don't get your fingers or your nose caught up in the belts or fans...

Is your's just normal?? Hard to answer that without hearing/feeling the vibration firsthand.

When the AC clutches in, there's clearly more load that the engine has to drive. In my '98, it's clearly audible combination of the radiator fan noise along with the engine having more load. I can feel some vibration when the AC is engaged, but not objectionable.

If you're accustomed to an escalade with a v-8 & 800 pounds of soundproofing - well, it's not ever gonna be like that. The power consumed by the AC is aboutthe same, but now the engine is smaller - so the AC is a larger percentage of the total engine power.

Other questions... Does it behave the same way idling in gear (holding the brake) vs. idling in neutral or park?

Don't forget to check the fans by shutting off the AC & making the fans run without the compressor. With everything shut off & cooled down, try shakingthe fan blades to see if their motor bearings are wobbly.

 

Thanks again, will do!