Adding oil to depleted A/C system

[JR]

So the system in the Mercury went TU last fall. A quick diagnosis confirmed loss of refrigerant but I left it at that as this vehicle rarely gets driven anymore, and we were all but out of A/C weather anyhow. This coming weekend I figure I will tackle it head on and get it back operational. The time has come...and then some!

I had some unexpected down time today so I figured I'd get a head start on the diagnosis aspect. Put the manifold gauges on and it was showing less than 10 psi static. After disposing of what was left I hooked up the vacuum pump to attempt to pull the system down before adding any freon or dye. To my surprise it quickly pulled down to 30in hg so I let it go for a while longer as it's been down 8-10 months. I've got some SAE certified dye to inject along with the freon but got to wondering how much oil if any I should add back to the system before running. This is a largish system by vehicle standards. Total system capacity 16 oz PAG oil, 47 oz R134. Is there a general rule of thumb how much oil to add back when a system has been depleted such as mine?

Thank you as always

 

[DavidC]

Are there signs of leakage ?. If not oil is not needed. To much oil can be detrimental to the cooling efficiency so tread carefully.

 

[Wayne M.]

Don’t add any. If you do a fast release of Freon, the oil gets carried out with it. Since it’s a small leak with no signs of wetness, say at the compressor, I’d leave it alone and charge it up with the dye included.

 

[JR]

Are there signs of leakage ?

I can't honestly answer this, the system just up and quit and all I did was throw a set of gauges on to confirm a system leakage. Now nearly a year later it would be impossible to tell if/where there was leakage.

The gills are green to no end over here so bear with me on this question, just trying to confirm, between a system leak down AND a solid 40 minute vacuum no appreciable oil is lost? Vacuum system down, add dye and freon and commence?

 

[DavidC]

If you do not notice any appreciable grimy spots or fresh oil do your normal routine. Vacuum,dye and freon and move on. When I do compressors I pour out the oil and measure then compare with replacement on whether to add oil or not. Of course all of the rest of the system has a coating of oil from use but there is no way to actually know how much so it would be very difficult to approximate.

 

[JR]

Of course all of the rest of the system has a coating of oil from use but there is no way to actually know how much so it would be very difficult to approximate.

This is my concern, that some (how much?) Oil is lost, and that it is difficult to approximate. But apparently it is not an issue.

Thanks guys!

 

[JR]

I will also add that going on 6 hrs the vac gauge has not noticeably moved. So it is a slow leak. Hoping the dye shows the problem area, as it is designed to do.

 

[DavidC]

I will also add that going on 6 hrs the vac gauge has not noticeably moved. So it is a slow leak. Hoping the dye shows the problem area, as it is designed to do.

Never saw a slow leak lose oil as it is the freon leaking and most of the oil is in the compressor. Now if it is a seal on the compressor and requires replacement then you will have to measure old and new as the new will probably have more and you will need to match as close as you can to not over oil.

 

[RVTRKN]

A catastrophic leak would have 0 PSI, no VAC is needed anyway if positive pressure was still in it. But you lost a lot of refrigerant somewhere, so maybe a seal on the hose connections. You could have charged it back to normal and see what happens, but you already pulled a VAC. Charge it and see what happens, worse case your compressor has a lot of wear with debris, and it will cause a restriction at the metering device screen. Just saw that happen recently.

 

[JR]

A catastrophic leak would have 0 PSI, no VAC is needed anyway if positive pressure was still in it. But you lost a lot of refrigerant somewhere, so maybe a seal on the hose connections. You could have charged it back to normal and see what happens, but you already pulled a VAC. Charge it and see what happens, worse case your compressor has a lot of wear with debris, and it will cause a restriction at the metering device screen. Just saw that happen recently.

I Didn't have much faith in the gauge reading hence the decision to vac. The vehicle had been sitting out in the hot sun when pulled in the garage, and when I opened up the low side there was very little to recover. So I figured better safe than sorry.

FWIW the compressor is dry looking.

I've done a visual on the lines from what I can see they look to be in excellent shape.
So I'm hoping for a faulty o ring but there is a lot that I can not easily get an eye on. I doubt I'll get that lucky, or have such an easy repair.

But we can all dream

 

[DavidC]

If it has schraders that is a common leak area.

 

[mfurrh55]

Whden my fan clutch went out, my ac system evacuated itself, got new fan clutch and charged system , no leaks in over a yr.

 

[jgillott]

JR, how deep were you able to pull the vacuum?

On edit: This is cut and paste from my EPA 609 manual.

"The system should be properly leak tested before charging with refrigerant. The system should hold a deep vacuum (27 in HG. or more) for at least one minute before charging. If the system will not hold a deep vacuum, a minimum amount of refrigerant (enough to produce a positive pressure) can be added for leak testing. An alternate method of leak testing is to use Nitrogen (an inert gas) to pressurize the system, and then pinpoint leaks with a soap and water solution. Whenever dry nitrogen from a cylinder is used in a service procedure, you should always charge through a pressure regulator, and have a pressure relief valve installed downstream from the regulator. NEVER pressurize the system with oxygen or compressed air."

 

[JR]

I got it to pull just shy of 30in. Ended up leaving it at that overnight, just went out and checked and it's still holding 27-28in. So a small leak somewhere.

I'm going to charge it with 134 to make sure all systems still work as intended in the event something else has gone TU since last fall.
Like to only open this thing up once if possible.

 

[jgillott]

I got it to pull just shy of 30in. Ended up leaving it at that overnight, just went out and checked and it's still holding 27-28in. So a small leak somewhere.

I'm going to charge it with 134 to make sure all systems still work as intended in the event something else has gone TU since last fall.
Like to only open this thing up once if possible.

It's not much of a leak if you were able to hold that much over night. Charge it, run some dye through, and I think it will be successful for you.

 

[mfurrh55]

Guess I should have paid attention in the original post....this ain't a ram, Take care

 

[RVTRKN]

Ya, I saw it is a Mercury. None the less purge the first little bit of 134a from high to low venting it out from the low side, then let out the refrigerant until just above 0 psi, then charge the weight of required refrigerant. This will help, if any leak allowed atmosphere into the system from evacuating, from any small leaks.

 

[B.G. Smith]

I see it's A Merc, if it's a Gran Marquise I might have a tip for you. Have an 05, had been adding 134 occasionally over a couple year period. Checked with detector many times and could never find the leak . Finally decided it must be the evaporator so I replaced that, to get warranty on evaporator you must also change the accumulator/receiver dryer. When I removed the accumulator found it to be one large rust bucket, it is located directly under the battery and has an insulation cover so it probably stays wet most of the time and may have received some acid from the battery above. By the way, the evaporator is not an easy item to replace. bg

 

[JR]

Thanks B.G. It is a Mountaineer with rear air.

Went out to add the charge today and popped a trans cooler line immediately upon start up. You cant make this stuff up! It is a line set coming directly out of the trans and only available as a set. The lines are a dealer only item and is 2-3 days out. So this job got shelved another few days.
Since I am close to a trans service I ordered a filter and a case of Fords super special Mercon SP fluid at around $10 a quart.

Strangely enough the vacuum gauge has not noticeably moved since this morning.

Odd?

 

[DavidC]

Murphy strikes again. He sure gets around, was in Minot ND the other day. Maybe that is all the vacuum can pull down with a dual system ie. front and rear air.