I am replacing my known-to-be-bad a/c compressor with a used believed-to-be-good one. How much pag oil do I need and how is it introduced into the system? I plan to have an independent mechanic introduce the refrigerant, so if the pag oil is routinely done during that process, perhaps that is the answer. But I don't want to assemble the system only to then learn that I should have introduced the pag oil at that time.

 

The new compressor often says how much oil it takes and what grade/weight.
The typical Delphi unit used on MINI's says 140 mL (4.75 fluid oz) of ND-8 which is a Denso oil similar to PAG46.

Some compressors come pre filled and some don't. Only way to know is try to pour the oil out of the new compressor into a clean cup (I use a plastic beaker with a pour spout). Then measure that and fill to spec. Some people like to measure how much oil came out of the old compressor and put the same amount back to (sort of) adjust for the oil spread around the system, but I'm afraid that a leaky system will be low on oil so this will start you low. If you are replacing the drier also (and you should!) then the factory fill is probably close to correct.

If you post the specific model compressor you have you might get a specific answer.

 

Thanks. Since the compressor I am installing is a used one, and I assume was subject to vacuum prior to being removed, I don't expect to find any oil in it. It is an OE Delphi. I can't read the model number on it, but do see where it says ND8 is acceptable.

 

Most of the oil will not be sucked out by vacuum. Most AC vacuum pumps are oil filled ... They pick oil that doesn't evaporate that easily ....

Given what you said, maybe "rinse" it with one dose of oil, spin it by hand, dump that out, then fill it with the factory fill.

 

I replaced with new but process is the same. Bring the oil to the tech and they'll do the rest. Mine warned against adding too much oil given the small capacity of the MINI system, thus oil displacing R134a volume.

 

Eric: So what you are saying is that the oil can be introduced after the system is 'buttoned-ed up?'

 

I installed a good used one from eBay. And it worked fine. Being it had some residual oil in the system I added 2.5 oz. and turned the compressor by hand to distribute the oil. 4 months later still blowing ice cold air. BTW I installed a new dryer as well.
Have you checked to make sure it's just not the clutch coil in the compressor? That's the most common failure. You can replace that without opening the system. eBay $90.00.

 

Yes, I know it is not the clutch. Yes, I am replacing the dryer.

 

New Problem: I had assumed that when the dealer diagnosed my failed compressor he left the system without any refrigerant. However, as I prepared today to dismantle the system I briefly depressed the center pin on one of the schrader valves and discovered pressure (and presumably refrigerant) still in the system. I am mindful of the environmental concerns and don't want to discharge into the air. What should I do? Car is half taken apart or I would drive to a service facility.

 

They might have left it under vacuum. Check first if it is sucking in or blowing out. Noise is about the same. Put a ballon or rubber glove over the fitting before you depress the valve.

I'm not very far from you and have a recovery machine. PM me if you want me to stop by. I'm partial to old Bordeaux but will settle for beer

 

Almost certainly pressure not vacuum. Will pm.

 

Many thanks to David.R53 for his assistance in evacuating my a/c system with the proper equipment. But question remains: how to properly introduce Pag oil into the used OE Delphi 9014 compressor (identical to what is being removed) that I am installing. I recently discovered a reference in a Delphi site that suggests that for some compressors there is a 'crank case plug' into which the oil is introduced. However, I could find no further info about this particular model. Anyone? And, that site also suggests that fitting threads and o-rings should be lubricated with '525 viscosity mineral oil' rather than compressor oil. Where do I get that? TIA.

 

I poured 2.5 oz right into the inlet side of the compressor before I installed the compressor. Then once it was buttoned up I turned the compressor several times by hand. As mentioned my used compressor is working like a champ. I pulled a vacuum on the system for about 30 minutes before adding the 14 oz of freon. I recommend vacuuming the system for an hour or two.

 

I skimmed through some of your questions just now. Some oil will reside in your system and used compressor. That's why I put 2.5 oz in mine but you might want to go 3-3.5. Also you vacuum a system after you install the compressor to pull moisture out of it that was introduced when you opened the system. I'm no expert, but what I provided here worked for my car

 

Thanks; which one is the inlet side?

 

If you are unsure on how to charge the system properly you need to find a shop to do it, introducing oil into the low side of the system will destroy the compressor, and being underfilled/overfilled on refrigerant can cause other symptoms you can't diagnose without the proper manifold gauges and recovery unit.

You will never know how much oil is truly in the system unless you remove the evaporator, condenser, compressor, drier and try to drain as much oil as possible and refill the system with the proper level of oil. Many times I have only added 50-60% of the requested oil level because of the variables involved, never an issue.

 

nkfry, inquiring minds want to know why introducing refrigerant oil on the low side will destroy the compressor. Here's a nationally known supplier's product that does just that:https://www.napaonline.com/napa/en/p...138_0200520219

 

Just like introducing a liquid form into the combustion chamber, liquid is not compressible, hence why fuel is vaporized and injected, not injected as a liquid.

Also, that isn't just PAG oil, it is PAG oil mixed with refrigerant being introduced as a vapor.

Straight PAG oil is liquid, and not compressible.

 

Concur. Hydrostatic lock occurs with liquid, hence, why folks should not drive a vehicle into deep water if they have an air filter pick-up down low. However, I did want to show the product that I linked is a way to introduce refrigerant oil into the system via the low side port.