I have looked through the questions to find an answer to my question and none of the questions seem to similar enough to this.

I have recently purchased a 2002 Subaru Impreza Rs and the car is doing something strange; while driving it will randomly, but consistently, "lose power" for a split second while driving. This can be in any gear, at a constant speed or while accelerating. I first started to notice this when I was driving with the music off. Every once in a while I would hear this faint "air release" noise and power would seem to "lag" for the smallest amount of time.

The only time this occurs is when the AC is on. This would lead me to believe that it would be an AC component. update below

The compressor seems to be working fine. The ac blows super cold, strong air and the ac works at idle and works on every setting.

I don't know much about the AC system and all its components so I don't really know where to go next. Could it be a leak somewhere that releases air when enough pressure is built up? Could some internal component of the compressor be slipping or seizing up? I asked a shop and they want to charge a few hundred bucks to put die in the system and check for leaks.

Any in site or direction would be much appreciated. Thank you for your time.


So as i have driven this car more I've been noticing a squeaky belt noise when I start the car for the first time after it sitting for a while. (mornings before work and after work to drive home) It usually lasts for about 15 or 20 seconds and is gone. This could be unrelated but i figured I'd through it in just in case.

The other thing I've noticed is that the issue explained above doesn't only happen when the AC is on. I've been driving with a bit more heat now that the weather is getting colder and it still does it when the fan is on. (When the fan is off I'm yet to notice it doing it)

I'm familiar with the load the AC system puts on the engine and it doesn't feel like that at all. The RPM's don't go down or anything when the problem occurs. It's just a little chirping noise.

My best idea still seems to be that the AC compressor has little mini-seizes every now and then. (That would definitely cause a load on the engine) However, if that were true I don't understand why this would happen with the fan on.

  • 3
    Have you tried taking the whole car apart and putting it back together?
    – LCIII
    Aug 15, 2014 at 16:10
  • Very nice IT Crowd nod there LCIII :-)
    – Rory Alsop
    Oct 14, 2014 at 22:21

3 Answers 3


I just wanted to give an update on this issue as it has been resolved.

First off, the noise actually got worse over this winter to where would happen for longer periods of time.

I ended up taking my car into the dealer to have then do a total inspection and diagnose the noise. First off it ended up not being A/C related at all. They said the noise was due to my belts not being under enough tension. They basically said, "the belts are new and whoever put them on didn't tension them down at all. That is where the noise came from."

What i suspect happened was they were tensioned down a bit and over time they slow became untensioned. Either way this is now solved.


Your AirCon compressor will cycle on and off, partly as a pressure control procedure. It will also cycle off on a full throttle. These cycle operations are usually imperceptable to the driving experiance.


As Allan pointed out, AC cycles on and off, but should have a negligible effect. If you are finding it causing engine problems the two areas to look are:

  • battery. It may be yours is on the way out, and the AC load pulls it below a threshold.
  • aircon. It could be faulty and causing far more load than expected.

Check the battery first - it's cheaper.

  • When the engine is running the battery is not involved at all . The alternator is doing all the electrical work.
    – Old_Fossil
    May 20, 2016 at 23:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .