Automotive Air Conditioning Information Forum

Hello, long time reader, first time poster. I have a 1995 OldsmoBuick Lesabre. Has been in the family since new, and is in great shape with 175k miles. I live in Phoenix and use it as my airport car. The car spent most of its life in a garage in the Midwest, until a few years ago when I acquired it.

History. AC clutch went out in 2015 and the compressor assembly was replaced with an “Omega” brand compressor. The system was vacuumed down, and charged by weight 39 oz. The AC worked well for the limited amount of use the car saw while an elderly owner (Grandpa) drove it. I know what your thinking, why didn’t you pull and replace the O/T and Accumulator? Wasn’t my call, just the wrench guy.

Fast forward to today. The AC is week at idle or parking lot speeds. The condenser has seen better days with about 20% fin damage from road debris. I had a local shop evac it for me, and I decided to tear into it.

Before that, the pressures at 95*F (Phoenix) was 55 LS / 225-250 HS. Engine RPM @1800 Vent temps 77*F. Going down the road, at 75 MPH after 20-30 min, the vent temp would be around 45* with outside temp of 105. But running errands at in town speeds and stop and go the vent temps are 75* on average. Cooling fans (twin fans) work and seem to move plenty of air. They kick on and stay on as soon as the AC clutch engages. When engine temp hits 210, both fans increase in speed even more.

I removed the condenser and accumulator today along with the original O/T, well, it was pretty bad. I took a pic, but unable to upload it. No metallic particles noted, just a black gritty mud. I used my AC blow gun filled with alcohol and flushed the OT line and evaporator, using a hose attached to the OT line into a milk jug to catch the fluid. It looked like Indian ink. Flushed a total of 4 times, and #4 ran clear alcohol.

I have a new accumulator, OT, and condenser. My question is what type of oil for the compressor? My research shows AC original uses PAG 150 and Denso uses PAG 46? I can’t find any info on the “omega” brand. The systems calls for 8 oz of oil. I have not pulled the compressor and assume there is oil in it? How much? My plan was to put 1 oz oil in condenser, 1 oz in evaporator, 2 oz in accumulator. Open to ideas and suggestions before I proceed with reassembly.

I have a refrigerant scale, gauge set, vac pump, keg of 134a and plan to vac and charge myself.

Thank you for any and all suggestions and help, enjoy reading the forum.
Mark

Black gritty mud means burned oil.
Suspect system lacked proper oiling, perhaps due to low charge.
If you encounter any grit, the compressor is coming apart.
The oil wgt is dependent on the comp mfg, not the FSM. Only the comp needs oil.
Are you sure there is no model number on the comp? Omega is a huge outfit here in TX. Prolly offshore with their label.
Your lo side is obv too high.

Comp needs to be removed and flushed with the oil you are gonna use several times. Do not use a solvent. Drain the old oil, then refill with new oil, rotate shaft a dozen times, drain it, and repeat until it drains clear.
Rest of system needs proper flushing, which it sounds like you have started on. Did you use absolute alcohol (100%)? Or off the shelf alcohol which is typically 70-90% alcohol and the rest is water. Water is bad. Tim, the site owner and supplier, has pro grade flush and a gun available (ACKits.com). His prices are quite good. Be certain you have given a long drying time using a tank of oxygen free nitrogen (welding shop) and a regulator. Keep your pressure less than 100 psi. I would vacuum an extra long time, such as at least 2 hrs. A vac of 30 minutes does little to boil off remaning water.

In Phoenix especially, you will see impaired cooling at low speed and stop and go. The comp needs to rev up in order to get much work done.
Would be nice if fans could be rigged to go to high speed right away. Be certain there are air dams around the condenser so that the air doesn't just walk around it to the rad. I am saying all this because with your ambients you need all the help you can get. We also see posters complaining of inadequate cooling but they are not on recirc. (Duh!)

Based on the oil that came out of the evaporator when you flushed it, I would want to start with a completely empty and clean system before evacuating and re-charging it. At a minimum, I would replace with new components the condenser, accumulator, and OT and thoroughly flush the rest. Does that mean replacing the compressor as well? The condition of the oil suggests that the compressor might be at the early stages of internal disintegration. But that's only a guess. You could take a chance on flushing and re-installing it. But if it fails and sends debris downstream, you'll have to do the job over while replacing the compressor with a new one (not a rebuilt) anyway. If it were mine, I wouldn't trust it.

Thank you for the advice. The OT was original, meaning it had never been replaced, same with the accumulator. When the compressor was changed, they were not. So the debris is from 27 yrs of service. As mentioned I have a new OT, Accumulator and Condenser. I will pull the compressor and flush as recommended. I use 90% alcohol, use nitrogen to dry, and always pull a deep vacuum after a flush.

"So the debris is from 27 yrs of service."

Maybe. I stopped short of suggesting a new comp. I was leary of it. John would change it, and were it my system, I would also. Your call

Please keep us posted.

Compressor is 7 yrs old with around 8K miles on it. I will pull it and flush it and see what comes out. I think the compressor is performing fine, considering the blocked OT.

" I use 90% alcohol, use nitrogen to dry, and always pull a deep vacuum after a flush."

Good.

Don't flush the compressor with the alcohol or any other volatile solvent, though. Use only PAG oil for that purpose, whatever viscosity you decide to put into the system.

Thnak’s John, that my plan. I need to find what oil is used is this compressor. Would you weigh the oil that initially drains out and reinstall that! Or will the nomenclature plate have the oil qty on it?

I wouldn't worry about how much oil comes out since you'll be starting with a dry system, unless you're curious.

Measure the oil in fluid ounces, not in ounces of weight like the refrigerant.

The compressor data plate should state the total amount and viscosity of oil needed, which might or might not differ from what GM says. I didn't look it up, but I think you mentioned earlier that the spec was 8 ounces originally, which sounds about right.

If all the oil won't fit in the compressor, distribute some of it to the other major components: One ounce each in the evaporator and condenser, and two ounces in the accumulator.