Proper R134A Conversion for 124? - PeachParts Mercedes-Benz Forum

JamesDean · #1 05-21-2013, 08:23 AM

Hey everyone,

My 91 300D was retrofitted to 134a sometime in 2010 by the previous owner. (a shop did it, I have a receipt in my records book). I am not sure what work they all did. I know that the fittings are now quick disconnects and there is a sticker the calls out the amount of 134a and type of oil used.

When I bought the car in summer the a/c worked well. When I went to use it this spring I found that it had lost enough charge to make the compressor not engage. I bought some 134a and charged it back up and so far its doing alright. However at 85F its not the greatest...better than nothing but not as cold as my other proper 134a system'd cars.

I know MB made 134a 124's after 1993, so I believe proper parts would be available for my 300D. So here is my question, what parts would I all need?

I would imagine:
1) Condenser
2) Dryer/Accumulator
3) Proper 134a seals
4) Expansion valve

But what about lines and evaporator? I think the compressor is OK with 134a...

This is mostly a fact finding mission as I probably wont jump on this until sometime in the fall or even next year.

Thanks!

ds190 · #2 05-21-2013, 09:56 AM

Member ps2cho just did all that. Find his thread either here or benzworld dot org.

ps2cho · #3 05-21-2013, 10:45 AM

The condenser is no different other than the port locations. The 10pa17c Compressor requires new power steering mount, new manifold hose /w fuel cooling (if the diesels have it?) and the condenser.
My advice? Skip all that expense and do R12.

JamesDean · #4 05-21-2013, 11:00 AM

Hmm I thought there were a more improved condenser for the 134a cars...

At the moment the 134a is doing OK in the car. I think its still a bit low on charge. I keep meaning to check it when I get home from work but am too lazy/tired to do it.

I need to replace the bearings in the aux fans and probably clean out the condenser. I'm sure doing those two things will help much as well.

The only problem I have with R12 is availability and the fact that my normal mechanic doesnt do much with R12 anymore.

I had a small stock pile which went into the 420SEL..which leaked much of it out over time...

compu_85 · #5 05-21-2013, 01:59 PM

Diesels don't have the fuel cooler.

Does your 91 have a parallell flow condenser? My 91 did.

-J

JamesDean · #6 05-21-2013, 02:12 PM

Quote:

Originally Posted by compu_85

Diesels don't have the fuel cooler.

Does your 91 have a parallell flow condenser? My 91 did.

-J

This I am not sure of..how could I tell?

compu_85 · #7 05-21-2013, 03:08 PM

Look at the sides of the condenser. If you see a bunch of tube elbos it's not parallell flow.

-J

JamesDean · #8 05-21-2013, 03:16 PM

I had to google it..which led me back the forum!

Evidently non parallel flow units are called serpentine flow..

ps2cho · #9 05-21-2013, 05:46 PM

R12 is readily available on craigslist everywhere. Just buy it with intent to resell and sell it to your mechanic for $0.01.

No w124 came with parallel flow. They are both tube and fin. We have the worst and that's why our conversions just plain suck. Its commonly thought that the later condensers were bigger or better, they aren't; they just changed the location of the hoses and added the more powerful 23/25 amp twin fan assembly with shroud.

Here is the later model condenser -- tube and fin:

lorainfurniture · #10 05-21-2013, 07:16 PM

Do you know what oil they put in? If they put ester oil, re converting is as simple as pumping down and recharging with r12.

I'd be happy to help you with it as I have all the equipment to do it

JamesDean · #11 05-21-2013, 11:51 PM

I was just looking in the EPC...Everything is the same from my 91 to the 95 E300D. Same part number for the evaporator, compressor and condenser. Damn.

Its on the label. I'll have to see. I for certain would need to replace some seals though. It was charged before winter hit and after...not enough pressure to kick over the compressor so clearly a leak somewhere. I would definitely want to make sure everything is done proper before putting some R12 down there.

I was down that path with the 420SEL. I *thought* everything was taken care of but...I still had to sink 3 cans in it a year later...

lorainfurniture · #12 05-22-2013, 12:05 AM

Charging with nitrogen is a whole lot cheaper than r12. Pressure testing IMO is the best way. 180psi solid for 24 hrs = victory.

I'd throw 1 can of 134 with some dye in it and check the leaks with a black light. Once it cycles a few times the dye will show.

I charged my car 4 times with nitrogen before I found every last leak. My ac is still ice cold.

JamesDean · #13 05-22-2013, 08:31 AM

Does your 300E have the 10P15C or 10P17C compressor?

I found this comment on the two:

Quote:

Originally Posted by stevebfl

I have converted hundreds of cars to 134, maybe a thousand. Probably a hundred 300Es. BUT I haven't done a pre 1990 300E in almost 2 years. I do not do them if they have the 10p15c or 10pa15c compressors. This is writen on the back head of the compressor. These small compressors do not handle the extra load well; they didn't do great in R12 and they ABSOLUTELY will not do better in R134a. There is an absolute 5% decrease in thermal efficiency with R134a.

If you wish to convert (DON"T do it) fix your system first in R12 till it is cold enough to suit you and then make your decision.

Quote:

Originally Posted by Air&Road

I was looking at a 92 300D one time that was factory 134a. For all I know it was the last 92 model ever made.

The later models use a 10P17 compressor. By changing the bracketry on an earlier engine, you can use this compressor. The mount holes are farther apart fore and aft than those of a 10P15 or 10PA15.

I am almost thinking about researching swapping the 15 out for the 17. My 420SEL has the 17 with R12, which does very very well.

However, keeping the 15, I think eventually that is the path I will take.

Replace every seal.
Remove the evap, clean it out.
Remove the condenser, clean it out.
Replace the schrader valves. Actually it has quick-connects on it now..
Pressure test. Is there any reason you chose 180 psi as opposed to something higher?
Verify
Verify
Charge with R12.

Today on the way up I stuck a thermometer in the center vent. 72F outside 74% humidity, at highway speed, I got about 48 at the vent. So a 24F temperature differential. Not horrible, but probably not as good as R12 or the ES-12A that I have in the 190E. I will get another reading on the way home today where it will undoubtedly be warmer. Tomorrow I'll be in the 190E so I can get that data as well.

Based on the charts provided in the 88-608 pdf:

At my conditions I should expect to see:
40% - 90% (Humidity)
260 PSI - 320 PSI (High)
14 PSI - 30 PSI (Low)
40 F - 46 F (Vent)

I believe there is a 10-15% efficiency loss with 134A...so my numbers were on par with what would be expected?

lorainfurniture · #14 05-22-2013, 10:25 AM

Removing the evap requires dash removal.- Not worth it unless you are replacing it.
Replacing seals is time consuming but very straight forward.
I would try and unscrew the quick connect and revert to the original setup. Its one less conection ie. place to leak. Also, a mechanic will think the charge is r134

I chose 180psi because I believe that is a reasonable limit to the low side. Any and every leak will show up at 180 psi. There is no need to go higher.

If it hold dead-nuts 180psi for 2 days then it is good.

Replace receiver/drier, pump down. Fill with nitrogen, pump down. Repeat 3 times.

If I remember, 3 cans of r12 from ebay is the perfect amount. I believe they where 12 oz each. The w124 is 2 lbs I believe, but there is a bit of waste in the can and in the hoses etc.

compu_85 · #15 05-22-2013, 10:57 AM

Quote:

Originally Posted by JamesDean

Does your 300E have the 10P15C or 10P17C compressor?

Great find! Offtopic I suppose, but my 91 350SDL has the 10P17C. The parts listing said that compressor was also used on the 6 cylinder R129 cars and W140 Diesels, which would have been R134a from the factory.

-J