Chrysler Repair: 1991 5th AC Noise, loose clutch, internal vibration

Question
Hello, and thanks for your assistance in advance.  I rebuilt my AC system, including compresser, expansion valve, high and low pressure cutoff switches, and condenser. When all parts were in place, I vacuumed the system to -30 for about an hour.  I then added 8 oz of oil(the pressurized can type) as per the company that rebuilt the compresser.  I then added almost two cans of R12.  The manifold gauges seem to be in the correct zone as per the shop manual.  

When at idol in drive, sometimes it starts to make a very strange noise that is hard to explain.  Seems like some internal vibration that eventually gets louder like a train comming through.  It also seems like it is comming from inside the system and not external.  Step on the gas, and it goes away.

This is a 1991 5th ave w/ 3.3L.  It is a variable displacment compressor.  It didnt do this before I made the changes.



Thanks for your assistance,

Chris


Answer
Hi Chris,
I personally have not experienced a sound like that, nor am I expert in A/C systems. The shop manual however says that noises in these systems can be misleading. Loose bolts, nuts, mounting brackets or a loose clutch assembly may be the cause of something that you suspect to be a failed bearing. Improper belt tension can be the cause of a suspected internal problem. Belt drives are speed sensitive so checking the tension of the belt would be good to do particularly because that engine's belt 'runs it all'. Also check that the plumbing is not rubbing other parts. I hope one of these will be helpful.
Roland
PS I just had a local ac/radiator shop recharge my 2.5L '89's system.  (first time in 10 year so I consider myself fortunate). The cost was $240 or which $150 was for R12, $5 for oil, and $85 for labor. It was interesting to watch the process.