Automotive Air Conditioning Information Forum

I really could use some help on this mystery..........

A month ago I replaced the following:
AC Compressor - ACDelco
AC Receiver/Drier - Toughone
AC Orifice Tube - Toughone
AC Condensor - Toughone

Because I replaced all of that and i flushed out the lines I added 9oz of PAG150 per references found here, http://www.4s.com/media/4981741/Four-Se ... -Guide.pdf, and here, http://www.techchoiceparts.com/refriger ... es/pontiac.

I vac'd the system for 15 minutes and let it sit overnight to check for leaks. Once satisfied it was leak free I vac'd the system for 45 minutes and then charged the system with 2.2 lbs of R134 per the under hood sticker using low side port and a set of gauges. Note that I use a large 30lb container of R134 and a digital scale to precisely measure the amount of refrigerant installed.

The ac worked awesome but when the compressor is engaged and the rpms exceed 2000 a whirring or humming noise came from the compressor. It got increasingly loud as the rpms rose. It is most definitely the ac system as the sound immediately stops when the compressor is disengaged.

This is not the first time I have charged an ac system, but just to be safe I had a shop evac the system and re-charge it using their "professional" equipment. The noise persisted and the shop agreed that I simply got a defective compressor. At this point they removed all of the refrigerant so that I could replace the compressor under warranty.

I just installed another brand new ACDelco compressor and then followed that same procedure above to leak test, evac and charge the system. Note that this time I drained the PAG oil from the first new compressor and measured it. I added the measured amount of new PAG oil to the second new compressor before installing it.

Once again the ac system works great, but the whirring noise is still present. For reference the temperature at the time of the second system charge was 80 degrees with low humidity. After the charge the low side pressure was 43 and and the high side as 175. Also, I did note that the system stopped inhaling refrigerant about 3 oz short of the 2.2lbs.

I know it's possible that I got a second defective compressor, but I feel it's unlikely. Any thoughts?

You might have inadvertently added too much oil to the system, which could be causing the strange whirring noise and out-of-whack pressures.

You said that you added 9 ounces of PAG 150 (the spec for the TOTAL amount) during the initial rebuild. Did you remember to check whether the first new compressor was empty of oil? If not, the new compressor might have had as much as 6 ounces of oil already in it from the factory. Adding 9 ounces to that would result in a significant oil overcharge.

Later, you said that you drained and measured the oil from the first new compressor, then added the same measured amount to the second compressor. So as before, if the second new compressor already had as much as 6 ounces of oil already in it, plus the oil from the first overcharge--much of which distributed itself throughout the system during the month you ran it--would have added even more oil to an already oil-overcharged system.

Generally, at an ambient temperature of 80 degrees, I would expect a low side of around 30 PSI and a high side of around 200 PSI. Your low side seems a bit high and the high side a bit low. Those pressures could be caused by the system refusing to take the last few ounces of refrigerant, which in turn could be caused by an oil overcharge.

Thanks for the replies.

Tony, I wouldn't want to just run it like it is for fear of damaging the compressor.

John, The first compressor came with with approx 2oz of oil which I drained before refilling with the 9oz. The second compressor came empty according to the instructions. I did verify it was empty before adding the 3oz. What you say makes sense. Do you think sucking out a few ounces of refrigerant and testing for the noise would be a reasonable approach? If that resolves the issue I could then fully evac the system, remove the compressor and drain 2 or 3 oz and then recharge.