Volkswagen: 1999 VW Jetta AC system, vw jetta, screw driver

Question
My jetta's AC system makes a moaning/wailing noise when turned on. It mostly makes this noise at an idle, at least that's when I hear it the most. It may be making the noise when running and I can't hear it. What is going on and is it a sign of something going bad? This is not the original AC system. It was replaced about 2 years ago.
Please advise and Thanks.

Answer
Here is the best way to diagnose this problem:


Get a long screw-driver.

Turn on the A/C with the motor running.

CAREFULLY, place the tip of the long screwdriver on top of the A/C compressor. (the device that is being spun by the belt)

Have someone turn on / off the A/C and wait for the infamous moan sound.   Put your ear to the other end of the screwdriver, and if you hear a lound whine,  you know that it's time for a new compressor.  (you will hear it clear as day, just like a stethoscope!)

If you are uncomfortable around the engine, by no means try this.

If you have a general knowledge of what parts are moving,  don't have a necktie on, have a steady hand, excersize common sense and caution, and you will have no troubles.

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If this is where the sound is coming from:

1) Have your refrigerant level checked first,  you may luck out, and just need a slight charge.

2) If refrigerant is OK, you are going to have to have the compressor serviced or replaced.


If this is not where the sound is coming from:

1) Have someone operate the A/C (on/off) and see if the belt is slipping when the engine is running.  If so, the belt simply needs to be replaced.


Troubleshoot this first, and please let me know how you make out.    


Ron