Charging AC with R12 - PeachParts Mercedes-Benz Forum

gottarollwithit · #1 07-08-2020, 02:20 AM

A year ago my mechanic flushed and rebuilt my AC system, new comp, shearer valves, expansion valve, receiver dryer, O rings, and flushed everything. Vacuumed it down and it held no prob for 15 min. 2 weeks later, my AC was low on charge.

Just sent leak hunting tonight. Put 65 psi of compressed air in the system (yes, I know, this is a no no”. A few hrs later it sunk to 60 psi.

Finally traced it back to a slow leak at the expansion valve. Foam on the piping around it was soaked in oil. Obviously the system slowly vented through there.

How much oil am I supposed to add??? I’m not sure how much leaked out, but it doesn’t look like much

tyl604 · #2 07-08-2020, 09:18 AM

Need more info. What car? What compressor? Diseasel300 is the expert here; you might send him a message.

resago2000 · #3 07-08-2020, 10:55 AM

I recharged my 240d with dustoff

Diseasel300 · #4 07-08-2020, 11:32 AM

Quote:

Originally Posted by tyl604

Need more info. What car? What compressor? Diseasel300 is the expert here; you might send him a message.

I'm far from an expert.

Diseasel300 · #5 07-08-2020, 11:41 AM

Quote:

Originally Posted by gottarollwithit

A year ago my mechanic flushed and rebuilt my AC system, new comp, shearer valves, expansion valve, receiver dryer, O rings, and flushed everything. Vacuumed it down and it held no prob for 15 min. 2 weeks later, my AC was low on charge.

Just sent leak hunting tonight. Put 65 psi of compressed air in the system (yes, I know, this is a no no”. A few hrs later it sunk to 60 psi.

Finally traced it back to a slow leak at the expansion valve. Foam on the piping around it was soaked in oil. Obviously the system slowly vented through there.

How much oil am I supposed to add??? I’m not sure how much leaked out, but it doesn’t look like much

Leaks are always checked under pressure with nitrogen. Vacuum tells you nothing about leaks. 15 minutes is too short of a period to know anything useful.

Bite the bullet and do the system properly. See if the expansion valve is leaking at one of the fittings, the body, or the power head. If the body or the power head are leaking, replace the expansion valve. Be aware that modern expansion valves are designed and drilled for R134a, they'll work with R12, but with reduced system capacity due to the smaller orifice, so it's worth seeing if your original is still serviceable. Replace every O-ring in the system. Use nylog on every O-ring. Flush all the lines with a suitable solvent and blow out thoroughly with compressed air. Replace the receiver/drier.

When complete, fill the system with oil according to the FSM. On the R4 cars, the oil is put throughout the system in various places and the FSM tells you how much to use and where to put it.

Once you're done with all that, THEN you can pressure test. Nitrogen will not change pressure with temperature (this is important for measuring a pressure drop). If the pressure in the system holds for 30 minutes with no change, you have a tight system. Release the nitrogen and move to vacuum.

When pulling vacuum, use a micron gauge if you have one. You're looking to get under 2000 microns for an old system, under 1000 for a freshly built one for a minimum of 15 minutes, preferably 30. If no micron gauge, make sure you pull down to -30PSI on your gauges and leave it for a minimum of 2 hours.

Now you can charge by weight since you're using R12. System capacity is located under the hood on a sticker. Be precise.

gottarollwithit · #6 07-08-2020, 02:00 PM

Sorry, this is for an 83’ w123 300d turbo.

I actually have done all of that, except the nitrogen part simply because I don’t have any. However, I did the full rebuild last year. Expansion valve was new, but one of the lines to it just needed to be tightened a 1/16 of a turn to fully seal it.

The question now is, without flushing and redoing all of that work, how much oil do I add? Just arbitrarily add 15ml?

jay_bob · #7 07-08-2020, 03:05 PM

I would not recommend using compressed air even for a pressure check. Even an 'oil free' compressor will have contaminants.

Either dry nitrogen or CO2 will work. I have heard of people using the party balloon helium cylinders too. Basically you want a dry gas that is safe for you to breathe (at least incidentally) and not ignite (i.e. oxygen or propane

).

But yeah break the whole thing down and do it right. I redid my W210 system back in 2016 and it was still going great when I sold the car last year.

ah-kay · #8 07-09-2020, 03:00 AM

This is what I do myself and it works with all my cars.

1) Pressurize the system to at least 90 to 100psi. The R134 pressure is at about 85psi when it is fully charged and car NOT running, low and high side should be at same pressure. No experience with R12.

2) Using nitrogen is ideal but not everyone has it. I use compress air. Don't frown on me because I have a laboratory grade vacuum pump. It can pump down to less than 100 micron. It can remove all moisture at such vacuum. I have never flushed an A/C system. I don't find it necessary. It is my opinion and mine alone.

3) Pressure should hold for 1 or 2 days. I do it myself so time is not an issue, unlike a shop.

4) Holding pressure does not mean it will hold vacuum. I run the vacuum pump for 90 minutes and making sure it holds for 1 day.

5) Most new system asks for about 8oz of oil. I normally put 4oz in a new compressor, assuming it has oil elsewhere.

I always charge 3/4 by weight of R12 specification when I convert to R134. A/C is not rocket science. Is it simple, NO. But most DIY amateur can handle it.

gottarollwithit · #9 07-09-2020, 03:42 AM

I’m well aware of what I am “supposed” to do in order for this to be perfect.
As it will take me several hours to disassemble, flush, replace the rec/dryer, then blow out the system, I simply do not see the utility in doing it. All this will achieve is ensuring a clean and dry system, but more importantly remove all of the oil, so I can refill it from zero.
This whole process was done about a year ago, albeit with a pinhole leak left in the system.
Before I added compressed air, there was still 10 psi of static R12 inside, so it never fully drained down, nor had the opportunity to suck gunk back through the pinhole. Point here is, the system is still quite clean and dry, just not perfect.

I’m not trying to achieve perfection, just a reasonably good and long lasting result. I know that compressed air was wrong for many reasons yet still did it. I’ll vacuum most of it out and whatever residual left in there I’m sure will shorten the life of my compressor.

That said, when the R12 leaked out through the tiny leak at the expansion valve hose connection, it took some oil with it. Looks like there’s about 1/2 an oz soaked into the foam for the expansion valve. Knowing that’s definitely imprecise, is that a reasonable amount to add?? Most AC systems have a window of acceptable volume of oil, I’m pretty sure that’ll get me close, yet keep it on the low range of that.

JHZR2 · #10 07-09-2020, 11:07 AM

IMO, the best reason to flush a system in a scenario like yours, is to be able to add oil back with confidence.

It is a hard thing to determine. Flush the lines, compressor, etc., and perhaps its a bit less chance for error.

My expansion valve also has leaked out oil. So Im in the same boat. So thus why Im thinking about this too... And at minimum Ill replace the R/D, flush the lines I can, etc. Since my compressor has very nice seals, that is the one wildcard, as its a set of joints that might not be prudent to take apart...

Mxfrank · #11 07-09-2020, 01:06 PM

Where are you getting R12?

gottarollwithit · #12 07-09-2020, 02:06 PM

I got a tank from back in the day....

The problem with tinkering with this system is that the evaporator core is basically inaccessible and the condenser is NLA thus aftermarket custom fit is the only replacement option. Plus, without physically disconnecting and maybe even removing the compressor, I don’t think I can realistically zero out the oil volume. As everything replaceable is one year/5 k mi old, I’m not gonna dig it all out.

I guess I’m looking for validation in the volume of oil to add?

Diseasel300 · #13 07-09-2020, 03:29 PM

My suggestion to purge the system and fill from scratch comes from the fact that the R4 compressor has no sump. It is totally dependent on oil circulating in the refrigerant system. Without starting from a known quantity, you're guessing. Your car, you do as you wish. Knowing the R4's dreadful service history, I'd be flushing and starting from scratch if it were mine. An A6, Sanden, or Denso would be a no-brainer to add a squirt since they have a sump.

vstech · #14 07-09-2020, 09:12 PM

Ok, in my opinion, you need a new dryer. It holds 3 oz oil, the expansion valve likely leaked out 2 oz oil. Compressed air has soaked your dryer desiccant, so it HAS to be replaced.
The air likely won’t make much more issue than that, IF you have repaired the leak verified for 24Hours under pressure with CO2 or dry N2. CO2 is easy to get at any Walmart or sporting goods store.
Really... it is worth it to get some, so you can change the dryer and know the system is dry after the vacuuming.

Yes, helium will work great, but it’ll find leaks R12 won’t leak out of. Nitrogen is the best... but not everyone can afford to get it. Any HVAC truck will have it in stock... maybe bum some from a tech?

How long do you want to keep the car? With moisture in the system, the oil will become acidic and DESTROY the impossible to replace evaporator coil...

gottarollwithit · #15 07-09-2020, 09:26 PM

I think that's a reasonable approach. If i put in a new rec/dryer, how much oil should i add?

Usually the Behr ones come with oil already in them, right?