Can PAG oil be added to a still cold blowing ac system?
 

Hi.

My ac compressor is compressing ok. Air in car is cold. I have no idea what the charge level is nor the hi or low side pressures as the system has never required a recharge and putting my gauges on the Schrader valves will likely leave them jammed open or shall I say not completely closed and all of my refrigerant will disappear.

The reason I ask is because my compressor sounds absolutely awful. Quite a metal on metal sound. I'm wondering if after 22 years, the PAG oil in there has broken down. Of course there's a bearing in there but I don't know if AC compressors for cars have sealed bearings or weather they are not sealed and that is why you put the PAG oil in.

Anyone? Anyone?

You probably need to open it up. The seals on the pistons start to come apart and plug the expansion valve or the orifice tube which ever you have. If the compressor is noisy it needs to be replaced. The oil needs to cover everything in the system. You might try a can of oil mixed with freon and see if that helps the noise but I doubt it will help.

I might just try that.

Thank you. Andy.

I'd take a close look at the clutch on the compressor first. When they wear out, they make a hell of a racket. I THINK you can replace it in the car if it's gone bad. I'm not sure as I don't have a Saturn to look at.

Will check

Agree with Rubehayseed. If you do not have a leak in the HVAC system, you do not need to add more PAG. Are you 100% confident that the compressor is the source of the noise? Have you attempted to start the engine (briefly) without the serpentine belt to confirm it is not internal engine? Have you attempted to hand spin each belt-driven accessory (with engine off of course) to feel or listen for bearing noise?

Thank you, md.

I drove this Satty off the lot in 97. One factory rebuit engine (180k) later and all 265k on the clock, I'm pretty familiar with the noises under the hood, though b c it is the original AC compressor, I don't know what a dying one or a dying clutch sounds like.

The engine burns no oil, runs synthetic 10w30 and is only started on warm winter days. It is my spare long since paid off ride, so it doesn't get that much use.

Background out of the way, your troubleshooting steps are sound. I try to keep this ride 100% functional at all times so that I can justify to the Mrs when I DO spend money on it that is money spent towards increased longevity and drive comfort..

The question behind my question was whether or not more PAG oil might be needed because the original had broken down physically or chemically and was therefore no longer providing adequate lubrication.

The last time I changed the serp was about 20k ago, and all pulleys checked out. I know I run the risk of spraying fragments throughout the system shut the compressor sale internally, thereby costing me a condenser and who knows what else along with a dryer. For right now, I'm taking that chance though I suppose I should pick up a new AC compressor while they are still available to go with the rest of my cache. of Saturn S car parts.

Does it make the noise if the a/c is off? If not, it's easy enough to check the clutch. Just stand beside the engine with the hood open and have someone start the car. Let it run for a minute or two and then have them turn on the a/c while you watch the clutch. If it pull in and starts making a racket, then you know that's what it is. I have limited knowledge of a/c systems, but have seen enough bad clutches to know how to listen and what to look for. With the engine off and the belt off, it should free spin. If it catches or won't turn, that's what I would suspect. Sorry, but I can't answer your question about the PAG oil. I would think that as long as there's no leaks, no oil should have been lost or need topping off.

Unlike engine oil, compressor oil is not subject to the kind of heat that can cause breakdown. Neither is it subject to the accumulation of combustion byproducts which also will break down engine oil.
Unless you have a leak there will be no reason to add more. However it can get contaminated with particles from compressor wear, hose and seal breakdown and water if the system has ever been opened and not drawn down properly before refrigerant refill. In that case the old oil will need to be flushed and replaced.

Thank you, sir