AC Compressor vibration just off idle

[BuickMike]

So this is my second compressor that is doing the same thing. Both have been AC Delco service compressors. Last time I used R12 and mineral oil. That compressor ended up locking up on me. This time I used R134A and PAG 150 per the instructions. I flushed everything out, pulled vacuum, it held, charged to correct pressure per chart, etc. Actually I got a lot of good info from CharlieF1 on AC maintenance. According to the instructions attached to the compressor, the whole system needs 8oz of oil total, 6 of which belongs in the dry compressor. I distributed the other 2oz in the evap and condenser. So now I have 2 compressors with different freon, different oil, and both make a vibration / humming sound just off idle. Keep in mind this is only when they are on. I also replaced the idler pulley with a good OEM style one just to make sure that was not the problem.

Anyone have some ideas?

 

[charlief1]

Did you use a new or remanned unit Mike?

 

[BuickMike]

Both of them are brand new ac delco units from nos4gn

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[BuickMike]

And who's Bob?

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[BuickMike]

Ok, so I've been Googling on the R4 compressors in general and it seems like this noise is commonly caused by a loose belt or a loose bolt on the compressor or the bracket. Here are some of my own thoughts on what I should try:

I guess I need to remove the compressor again to check the bolts on the bracket

The bottom bolt on the compressor that connects it to the bracket (the long one) is a Ace hardware replacement. I couldn't find the original. Even though it is tight. this one may not be as thick as the original and may be causing some resonance?

Is there a way to tighten up the belt tensioner a little?

 

[charlief1]

The R4 compressor makes noise no matter what you do and there isn't a whole lot you can do about it. The bolt shouldn't make much difference. While the directions say put the majority of the oil in the compressor I only put a small amount in. PAG oil doesn't do like the old mineral oil and stay suspended in the refrigerant, it separates out and flows through the system in clumps. If the compressor happens to get one of those clumps then it will damage the compressor. This doesn't happen with R-12.

 

[BuickMike]

Is it just the service compressors that are noisy? My original one and the crappy Peb Boys one I used to replace it never had this issue. My Pep Boys one was actually still working, but I wanted a AC Delco one. At the time I didn't realize that the new AC Delco R4's are outscourced to China

 

[charlief1]

All the new compressors are out of china these days. Get a Delphi since that's who's supplying compressors to GM now.

 

[TexasT]

Is there a way to tighten up the belt tensioner a little?

Only way I know to tighten up is to go to a slightly shorter belt. The numbers on the belt part number have to do with belt dimensions. I've gotten a shorter one for my suburban so I'm sure you could do the same for the Buick.

Have you checked out the thread on the office duster(152a) in place of the 134a? Good info.

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[PSID6]

Ok, so I've been Googling on the R4 compressors in general and it seems like this noise is commonly caused by a loose belt or a loose bolt on the compressor or the bracket. Here are some of my own thoughts on what I should try:

I guess I need to remove the compressor again to check the bolts on the bracket

The bottom bolt on the compressor that connects it to the bracket (the long one) is a Ace hardware replacement. I couldn't find the original. Even though it is tight. this one may not be as thick as the original and may be causing some resonance?

Is there a way to tighten up the belt tensioner a little?

I chased a similar problem and it ended up being the bolts that hold the aluminum bracket to the head. 2 out of 3 where loose causing the bracket to vibrate.

 

[BuickMike]

I chased a similar problem and it ended up being the bolts that hold the aluminum bracket to the head. 2 out of 3 where loose causing the bracket to vibrate.

That was the first thing I checked. A slightly shorter belt may help. It is not very noticeable any more since I put a softer set of bushings on my HR drivers side mount and swapped the passenger mount for a OEM one.