Adding Oil to the AC System - PeachParts Mercedes-Benz Forum

shertex · #1 08-03-2011, 02:57 PM

I have a question about adding oil to the AC system (1991 300D retrofitted to R134a).

To anticipcate some responses (to save the flamers-in-waiting some typing)....

1. Yes, I know that a known leak should be properly repaired.

2. Yes, know that the only way to ensure the correct balance of refrigerant and oil is to evacuate and recharge the system and that I cannot assume that oil and refrigerant are leaking at the same rates....but perhaps even that doesn't ensure a correct balance??

Please humor me anyway.

When I purchased the vehicle in the Spring of 2009, the AC seemed weak so I added some refrigerant. I've since learned that I have a fairly slow leak. Maybe twice a year I add refrigerant and it blows nice and cold.

As a result, I have no real idea how much oil is left in the system. If I weren't so penny wise and pound foolish, I would just evac and recharge the system and get the leak diagnosed....which I may still do.

But if I don't, and if I want to live a bit dangerously, how would I go about making a guesstimate as to how much oil to add? System capacity is 2 oz. (plus 2 lbs. 4 oz. of refrigerant). Just refrigerant with the oil mixed in? Add an ounce every year or two? What's riskier: too much oil or too little?

I figure, on a car this old, the compressor isn't going to last forever anyway. So I'm willing to roll the dice to a degree. I know that what I'm supposed to do is let a professional deal with this....but I just don't want to spend the money.

Thanks.

boneheaddoctor · #2 08-03-2011, 03:50 PM

Quote:

Originally Posted by shertex

I have a question about adding oil to the AC system (1991 300D retrofitted to R134a).

To anticipcate some responses (to save the flamers-in-waiting some typing)....

1. Yes, I know that a known leak should be properly repaired.

2. Yes, know that the only way to ensure the correct balance of refrigerant and oil is to evacuate and recharge the system and that I cannot assume that oil and refrigerant are leaking at the same rates....but perhaps even that doesn't ensure a correct balance??Please humor me anyway.

When I purchased the vehicle in the Spring of 2009, the AC seemed weak so I added some refrigerant. I've since learned that I have a fairly slow leak. Maybe twice a year I add refrigerant and it blows nice and cold.

As a result, I have no real idea how much oil is left in the system. If I weren't so penny wise and pound foolish, I would just evac and recharge the system and get the leak diagnosed....which I may still do.

But if I don't, and if I want to live a bit dangerously, how would I go about making a guesstimate as to how much oil to add? System capacity is 2 oz. (plus 2 lbs. 4 oz. of refrigerant). Just refrigerant with the oil mixed in? Add an ounce every year or two? What's riskier: too much oil or too little?

I figure, on a car this old, the compressor isn't going to last forever anyway. So I'm willing to roll the dice to a degree. I know that what I'm supposed to do is let a professional deal with this....but I just don't want to spend the money.

Thanks.

Too much and you can kill the compressor suddenly with a slug of oil (oil won't compress)....too little and you burn it out more slowly.

and to the highlighted part.....you need to add FLUSH. You evacuate the system with it closed and use a vacuum pump. All the oil remains in the system, and you still don't know how much is actually in it as the reciever/drier and the compressor have oil as well.

Too much oil will also reduce capacity as it reduces space for refridgerant and the result is a system with less cooling capability.

jeffr0000 · #3 08-03-2011, 10:42 PM

I'm pretty sure the ac oil capacity is 8oz, not 2oz. I too am frustrated with the ac nazis around here. Was told i was terrible for testing my system on r12 when that's all I had. Ended up not getting the advice I needed and failed to replace the oil lost when I replaced the receiver/dryer. No one told me to measure out what was removed, only that a total flush and perfect balance would do. Anyway, it turns out I was low on ac oil, as evidenced by a noisy compressor. I bought an interdynamics ING3 tool to inject 2oz of ester and everything seems happy. My ac blows real nice and cold and the compressor doesn't make undue noise anymore.

This I can tell you, there is an optimum oil level, and it's worse to overfill than under, because liquids don't compress, but being a little under or a little over ain't the end if the world, and functioning ac if even for a little while is better than none because you don't have the coin to do it perfectly. I mean, if I can make it work and it's cheap, that's better than it not working at all, you know? And if it fails shortly after, no biggie, we're only right back where things were before, it's broke.

compress ignite · #4 08-04-2011, 01:36 AM

(And,I'll never fly commercial again.)

jeffr0000 · #5 08-04-2011, 08:32 AM

Quote:

Originally Posted by compress ignite

(And,I'll never fly commercial again.)

When a 240d becomes a commercial aircraft, let me know. It's not gonna fall out of the sky if the ac goes tits-up, it ain't gonna fall out of the sky if the engine ejects all it's spinning bits out the oil pan, because it's a car.

shertex · #6 08-04-2011, 08:53 AM

Quote:

Originally Posted by boneheaddoctor

and to the highlighted part.....you need to add FLUSH. You evacuate the system with it closed and use a vacuum pump. All the oil remains in the system, and you still don't know how much is actually in it as the reciever/drier and the compressor have oil as well.

That's right....I had forgotten about the flush part. Tells me there are probably a lot of people out there with nice cold AC that have the incorrect amount of oil in the system.

boneheaddoctor · #7 08-04-2011, 09:10 AM

Quote:

Originally Posted by shertex

That's right....I had forgotten about the flush part. Tells me there are probably a lot of people out there with nice cold AC that have the incorrect amount of oil in the system.

No doubt....but an experienced A/C guy can guess about how much each component contains as the oil is distributed through the entire system. and get it close when replacing a part or two.

SD Blue · #8 08-04-2011, 10:47 AM

This is just logical thinking and not advice. If your only losing a small amount, over a year, in a retrofitted system, you might be looking at a need for barrier-type hoses. But to "save" on cash, the easiest step to take would be using a sniffer to check for leaks. One is available, in this area, at auto parts stores for basically free rental.

After significant checking, then you might be able to basically "point-the-finger" at the hoses. Since there would be no oil loss through the hoses, then you might be safe to assume a "topping off" with refrigerant is all that is needed.

Run a sniffer over the system real well and note the number of "might be's, maybe's & assume" in this post and roll the dice. As with any roll of the dice, sometimes you get to keep your chips and other times the response is "Oh Crap".

nelbur · #9 08-04-2011, 05:42 PM

I think you can get a very rough feel for the oil circulating with the refrigerant by pressing or triggering the shrader valve to see how much oil comes out with the 134a, with the compressor running. If your conversion to 134a was done recently, and assuming it was done correctly, a full oil charge of 8 to 10 oz. should have been added and it will take years to lose all the oil charge through the leaks.

I have converted two 25+ year old R-12 vehicles to 134a. In both cases there was not a drop of oil in the dryer or the compressor, but both worked fine after the conversion. One has been sold but the other has about 3 years on the conversion and is working fine. I am sure the conversion happened just in time to save the compressor.

I have just added a 2oz. oil charge to my 13 year old Mercedes just out of general principles, based on what I found with the other old systems. The oil does leak away.

yuke · #10 08-04-2011, 06:08 PM

Where do add the oil at the condenser and drier? You have 2 lines on the condenser Low+High and 2 on drier does it make a differance where you add it at and what kind of oil do you put in Ester or Pag as I too am thinking about replacing my condenser and drier on my 85 300SD

jeffr0000 · #11 08-04-2011, 08:36 PM

Quote:

Originally Posted by yuke

Where do add the oil at the condenser and drier? You have 2 lines on the condenser Low+High and 2 on drier does it make a differance where you add it at and what kind of oil do you put in Ester or Pag as I too am thinking about replacing my condenser and drier on my 85 300SD

Ester is compatible with Pag and mineral, Pag is compatible with ester, mineral is compatible with ester. Go with ester if you don't know what's in there.

nelbur · #12 08-05-2011, 01:08 PM

Yuke, the easiest way to add oil is to get one of the small cans with a couple ozs of oil with a bit of 134a to force the oil in. The oil charge can fits the hose you use to add the 134a. Read the instructions. You will likely have to invert the can after you purge the air out of the hose with the 134a portion. You only add stuff into the low pressure side of the A/C system. The high pressure side might blow up the flimsy cans the refrigerant comes in. Of course, if you have R-12 in your A/C you will have to find an R-12 compatible oil charge which might be difficult.

jeffr0000 · #13 08-05-2011, 02:25 PM

Quote:

Originally Posted by nelbur

Of course, if you have R-12 in your A/C you will have to find an R-12 compatible oil charge which might be difficult.

Buy a bottle of oil and interdynamics ING3, you'll also need some sort of hose to connect the ING3 to the low side port of the A/C system.