R12 to R134a to R12 - PeachParts Mercedes-Benz Forum

Zoonhollis · #1 05-19-2003, 03:14 PM

It seems some shops would rather convert a Freon system to R134 than attempt to find the leak that prompted the conversion in the first place. Is this common? I live here in Texas where R134 is a joke in the summertime, and I would like my system BACK to R12. Other than replacing the drier and thoroughly flushing the system, what is required? I suspect that finding the leak would be a prerequisite as well...

#2 05-19-2003, 04:42 PM

Zoonhollis,

Welcome back to Texas, Grand Prairie I hope.

I have reverse converted before. Flush thoroughly to remove all oil. Remove the compressor and dump out as much oil as possible. Rinse with mineral oil by pouring it in and turning several turns by hand the pumping it out. Then install and put in the correct amount of mineral oil.

If the expansion valve and pressure switches have been changed to 134 items, you will need to change them back. Change filter drier, evacuate and charge.

All this hopefully will be done after finding and correcting the leak.

Good luck,

dave240 · #3 05-19-2003, 11:21 PM

Zoon,

My quess is that EVEN IF they were to fix your leak, who's to say another and another will not pop up. letting that precious R-12 to slip away each time.

I believe most of the components on the newest factory installed R-12 systems are already a decade old.

These shops figure they can get you to pay for a conversion, and with less risk to them should there be a leak.

Did the 134 not work well for you?
I was considering the conversion as I have a slow leak. but I still have a few lbs. of R-12 stashed.

#4 05-20-2003, 07:33 AM

Dave,

You do not say what model you have, but it seems from your signature that you have a 240D. These cars do NOT convert well at all. They just don't have enough reserve capacity.

In addition to that, the cars that require R12 are hitting the wrecking yards in large numbers every single day. This means that there are rapidly becoming fewer and fewer cars on the road that require R12. For that reason R12 is coming DOWN in price.

That said, even if it was still fifty bucks a pound, it is usually a small percentage of the overall repair cost. The fact that these cars have age on them does not mean the components will fail more AS LONG AS the leaks are properly repaired and the systems are PROPERLY EVACUATED before charging.

The worst leak producer is moisture in your system. The moisture combined with refrigerant creates an acid that will eat through components. It matters not if those components are brand new or 20 years old, the acid doesn't care.

The key to a good running R12 system then, is proper leak repair whatever that leak might be, followed by THOROUGH evacuation, a new filter drier. Do this properly and you could very well be ready to go for another 20 years.

Have a great day,

leathermang · #5 05-20-2003, 08:42 AM

How does one increase reserve capacity ?
Would putting two reciever/dryers ( in parallel ) help ?
Would putting a new condensor of the new parallel design help ?
Parallel is my new favorite word.

Zoonhollis · #6 05-20-2003, 09:15 AM

Thanks for the replies, Larry and others. I'm back in Ft. Worth on a contract at a local company, but my official address is NC.

The reconversion sounds pretty straightforward, but I'm uncertain about the correct amount of mineral oil to put back in the system upon recharging. Is there a chart that shows such a thing?

Larry, why don't you just drop by my place and do this for me?

leathermang · #7 05-20-2003, 09:45 AM

Join the crowd on the mineral oil measureing problem....
It is hard to find the amount from the manufacturer of many compressors as to the correct amount theirs needs in the crankcase...
The old York, had a dipstick to measure with ... ( or gave the dimensions so you could make one)

The newer ones... you almost need to flush JUST for being able to judge how much to put back in... there are some listings for general number of ounces for each part which is replaced in a repair...

Also, did you know that you are supposed to run the vacuum machine with the oil out of the compressor, then fill it with new oil before starting up..

This is because you don't want the oil exposed to the moisture in the system , while the vacuuming is happening... it could hold too much moisture for the long term......

Larry, yeah, why don't you go help this guy far from home without his tools... lets see if you are all talk/book learning....

( trying to help you out here , Zoonhollis... )

dave240 · #8 05-20-2003, 10:31 AM

Larry, thanks for the insightful comments.

I have the 1982 240d.

It is my understanding also, that the stock condenser coil on these 123's are not adequate for the 134 application.

"ParallelmanG" mentioned the "parallel flow" condenser which are suppose to work more effeciently and reduce head pressure on the compressor. And as I understand, 134 takes more energy to compress aswell.

Instead of two driers, howabout just an accumulator? Or would that require an orifice & new evap.coil?

Q. Does it help to remove the valve core when evacuating?

Q.Is 1 - 2 hrs long enough evac. time?

Q. Can reclaimed refrigerant be re-installed back into the system?

Q. Do I need a good book?

Zoon, do a search, I saw a thread on this a few days ago.
but of course it would depend on which brand you have. I thought I saw 6oz (maybe 8oz) for the R4. Not sure.
But I would certainly try to find manufacture specs. on that one.

dave

leathermang · #9 05-20-2003, 11:42 AM

I do not know if an accumulator would work.. they are associated with the different kind, as you mention, .... orifice tube type systems... but they require a different method of regulating the compressor.... ( I think )

Because 134 is a less efficient molecule than r12 , to keep the same parameters you would immediately need to increase your systems capacity by about 20 percent.... therefor it is my opinion also that these systems either need mechanical upgrade to deal with 134.. or should stick with r12 ( best option at this time imo)

No, you do not want to take out the valve core... how would you take your charging hose off your system without negating your work by it being open to the atmosphere ? ( and thus moisture )...

It depends on how much moisture is in the system... and how much vacuum you are able to pull...judgement calls in some instances... but the rule at my place is THE LONGER THE BETTER. Overnight preferred.

Reclaimed R12 can certainly be reused... however you need to check for NON condensable gases... not an easy thing to do... basically you put your gases under pressure and store over night at above a certain temp.. then you take the temp of the inside of the storage bottle at about 4 inches below the top... and you vent some until you get the right readings showing you are not "too " contaminated...

However, the venting process BY and OF itself reduces the temp of the gases ... so your system may need to be stabilized overnight to do each check.. the check involves reading the charts to see if your container is producing the proper pressure for the temp which it is at.... this is how you can tell if you are contaminated with non condensible gases ( like AIR )....

Technically all gases are condensible... you have seen Nitrogen in liquid form for saving important body fluids,,, etc....
But the term is used in the books with reference to OUR AUTO AC systems.... which are not capable of condensing Nitrogen ...

Do you need a good book... is this a TRICK QUESTION ? Emphatically yes,, including the AC service manual from MB.. ( in my opinion ).....

#10 05-20-2003, 12:18 PM

I was looking for the link on www.aircondition.com where I found a site that would give capacities for any system but I couldn't find it.

Anyway your late 123 with R4 compressor takes 8 ounces. As leathermang said if you don't flush EVERYTHING you are flying blind with guesswork knowing how much to put in. He also makes a good point about oil in last, but that's difficult to accomplish. If you have an injector like is used with dye, I suppose you could evacuate, charge into the vacuum, then inject the oil. I'm not sure, however, if the disconnect/reconnect wouldn't risk more moisture introduction than might be held in the oil. If you put the oil into a system that was otherwise assembled, then it wouldn't have much time to absorb moisture. Interesting suggestion to contemplate.

Related to the oil going in last is your question about how long to evacuate. If it is really hot weather, an hour or so will probably work pretty good. If it is cooler wieather you will probably need to warm components with a heat lamp to force the moisture to adequately boil off. Unless you're in Alaska this time of year, you should be able to evacuate acceptably in an hour. I'm with leathermang on this though, if you have a pump that will go overnight without overheating it would be worth the extra step IMHO.

Good luck,

leathermang · #11 05-20-2003, 12:21 PM

I was reading in my new 616 manual this weekend... so I am pretty sure the " oil in last" was in there.... the MB fsm... but will check on that...

Larry, your figure of 8 oz.. was for the compressor alone... right? He mentioned " system" so I brought up the other oil holders...

#12 05-20-2003, 12:52 PM

No the 8 oz. is for the whole empty system. I have done a few 123's with R4's using this quantity in a flushed system with good results. I know it doesn't sound like much but this is what was indicated and has worked for me.

You can go to aircondition.com and post any system and they will tell you the necessary volume.

You will see other oil holder quantities, but these are usually guidelines for how much per component. An example might be if you replace the condensor alone, you should add a certain quantity. This is like you projected as being guesswork. The only way you know for sure is after a complete flush, empty compressor and replace drier then put in correct amount.

Good luck,