Back to R12 worth it? - PeachParts Mercedes-Benz Forum

TJR300SD · #1 08-08-2007, 02:33 AM

Hi everyone,

This is my first post around here and I'm actually a new owner of a 1983 300SD. I got it from my dad who bought it about a year ago in very poor condition. Since then we've fixed it up and just recently we got the A/C repaired at a local Mercedes-Benz shop, who retrofitted the system to R134a. At idle the vent temperature is around 50 degrees, and at 1500 rpm it's about 40 degrees. This is actually the first time the A/C has been functional since it was purchased last year.

I know the system was originally designed for R12, so I was thinking of changing the refrigerant to R12 for maximum performance (very costly, I know). How much cooler would the vent temp be if the system had R12 instead? 30 degrees? 40 degrees at idle? I need it to be very cold because I'm moving to Phoenix where the ambient temp is around 100 degrees from May to September. I'm not sure that as it is the A/C will be adequate for that climate. Do you think it would be worth it to get R12 instead? Would it make a big enough difference in comfort?

Jeremy5848 · #2 08-08-2007, 03:15 AM

As you have indicated, the system was originally designed to use R12 and it will cool better with that refrigerant. My '85 has not been converted; I notice that it doesn't cool as well at idle as when moving. This is to be expected. One this to check is that the secondary fan turns on as designed as the pressure in the a/c system rises. The dealer who did the R134 conversion should have checked that. In my car, cooling is improved once the second fan kicks on. Personally, I would move to Phoenix first and see if the system works well enough. Why spend $1000 (or whatever it is) to fix something that doesn't need fixing?

tangofox007 · #3 08-08-2007, 06:49 AM

I converted back to R-12 last summer. It's been great to have a/c that actually works. The R-134a just did not cut it above 85*F.

ichbineinekrous · #4 08-08-2007, 07:44 AM

my r-134 system worked just fine yesterday here in Raleigh, it was 99. Vent temps as long as I was moving were mid-upper 40's. I think a system flush is just as critical, if not more, than the eventual refrigerant. My brother and I both recharged our cars at the exact same time side by side in the driveway. He did not flush, only changed out the dryer, and used r-12. I flushed everything and installed new compressor, dryer and expansion valve and used r-134, with frigi-quiet synthetic compressor oil. Neither car got very cold at idle, both were comparably cold once moving. The big thing was that even though the r-12 benz held vacuum initially, a small leak has depleted the refrigerant and it no longer gets cold. I've had to turn the ccu wheel up into the white on several trips through Virginia this summer, temps in the mid-nineties outside, high humidity. By the same token, when stuck in traffic and not moving, I've had to roll the windows down cuz the a/c just wasn't getting it done. I think this last bit has more to do with the size of the condensor and the heat coming off the engine and the weakish fan than any refrigerant consideration. Its not black and white is what I'm trying to say here, sorry it took so long to spit out.

NC Benz · #5 08-08-2007, 08:21 AM

Quote:

Originally Posted by tangofox007

I converted back to R-12 last summer. It's been great to have a/c that actually works. The R-134a just did not cut it above 85*F.

103 here yesterday with humidity. My vent temp was 54. Thats a 49 degree drop and on R134a. I am sure it would be better on R12. I am working on my sons 300D that has R12. Stay tuned on that one.

#6 08-08-2007, 09:03 AM

I also tried R-134a in my 300D, it was "OK" up to about 90F ambient, then it didn't really cut it. I converted back to R-12 a couple of years ago, much colder.

vstech · #7 08-08-2007, 09:03 AM

49 degree drop from 103 outside temp is a meaningless number. it states capacity is adequate to cool... depending on duration of run time. what temp was it INSIDE the car when the 49 temp was made, how long had the car been running? what was RPM of motor? how fast were you going?
134 is fine in AZ because there is almost no humidity. NC and VA are MUCH harder on ac systems than 100ish ambient. that said, 120°F is hot no matter what you do. and az gets there. if you don't want to go back to 12, plan on improving the condenser with a cross flow parallel condenser. and plan on replacing the compressor often.

tjohn · #8 08-08-2007, 09:12 AM

R-12 remains the gold standard IMHO, but I will say that during long idles the temperature used to creep up in stop and go on hot days. I believe, w/o having objective evidence, that I have helped that by switching the tiny aux fan on my 82 to the roughly 50% larger one from an 560 SEL. Yesterday we got to 98, and the system kept me completely comfortable in stop and go even in full business attire. I normally keep the dial just below 22, for what it's worth.

I've never been to Phoenix. All reports on this board and others indicate that you'll be taxing your system to its limits. I would consider the aux fan swap I mentioned (a quick snag at a pick and pull, get the bracket from the donor car and swap your horn to the new one). I would also make certain that the vents are performing properly. Many of our cars have problems in this area. I don't think your car has a dedicate recirculate button, but if the vents are working right, you'll get something close to it when you turn the dial to min. If the vents aren't working properly you get something like 80% outside air on min

Some claim the the R134a blend Freeze 12 performs better, if you don't want to do a full retrofit, with the flush and receiver/drier swap that is necessary when changing from R134a to R12, you may want to try that. Oh, and maybe tinted windows....

Mark DiSilvestro · #9 08-08-2007, 09:24 AM

Might also be able to rewire the aux fan to come on with the AC or a dash-mounted toggle-switch, not just when the system pressure gets high enough to activate the pressure-switch.

Happy Motoring, Mark

Tymbrymi · #10 08-08-2007, 09:27 AM

Quote:

Originally Posted by vstech

49 degree drop from 103 outside temp is a meaningless number. it states capacity is adequate to cool... depending on duration of run time. what temp was it INSIDE the car when the 49 temp was made, how long had the car been running? what was RPM of motor? how fast were you going?
134 is fine in AZ because there is almost no humidity. NC and VA are MUCH harder on ac systems than 100ish ambient. that said, 120°F is hot no matter what you do. and az gets there. if you don't want to go back to 12, plan on improving the condenser with a cross flow parallel condenser. and plan on replacing the compressor often.

I would just like to second all of this.

When referring to 'temp drop' it is not relative to the outside temperature. It is the temperature drop across the evaporator.

Also, my W116 has been converted to R134a by one of the PO's. In Mississippi it sucks. On the interstate it barely makes it to 60F. I drove that car to Phoenix and the A/C was AMAZING! It probably blew in the 50's in stop and go city traffic!

The parallel flow is the way to go from all that I've read. The people who have converted to that have always reported good results. Search around a bit and you'll find lots of info on it. I believe one of the best documented ones was by dmorrison (IIRC).

Edit: Yesterday it got to 99*F with 50% humidity....

ichbineinekrous · #11 08-08-2007, 09:42 AM

forcing the system to do 100 re-circulated air while in any of the a/c settings is a 30 min. fix, and one I would recommend to anyone wanting to maximize cooling. I agree that upgrading your condensor to a larger one is probably the most cost effective way to boost your car's ability to overcome hot ambient temps. If you can't expiate the heat energy from the refrigerant it cannot be compressed as much and that's the whole shootin' match, regardless of which flavor of refrig. But r-12 is better, if you don't mind paying a couple hundred bucks every couple years (if youre lucky) when u replace the compressor.

WD8CDH · #12 08-08-2007, 10:07 AM

The hydrocarbon refrigerants like Duracool are the only ones that are near the capacity of R-12 (sometimes better). I have converted several R-134 systems and one R-12 system to HC refrigerants with really good performance.

The HC refrigerants are a lot better for the environment than R-134 or R-12 too.

#13 08-08-2007, 10:14 AM

Using hydrocarbon refrigerants may be OK if you always plan on servicing the system yourself. It's my understanding that they are not legal for automotive applications in many states (including NY, I assume, because just about everything is illegal there). I suspect you would have a problem getting a reputable shop to touch the system after it was converted.

I would recommend R-12, the only downside is the cost and it's really not that bad, maybe $150-200 for a charge.

rrgrassi · #14 08-08-2007, 10:26 AM

The aux fan kicks in when the TEMP of the freon hits a certian temp, not by pressure. Pressure is what controls the compressor. On our cars it was only if the freon pressure was too low that the compressor is shut down. I installed a hi/low switch that kills the compressor connection if the pressure is either too high (which happens w/134a) or too low (usually caused by a leak).

funola · #15 08-08-2007, 10:28 AM

Why are hydrocarbon refrigerants illegal for automotive use in most states? I have read that it is widely used in Europe.

Quote:

Originally Posted by Craig

Using hydrocarbon refrigerants may be OK if you always plan on servicing the system yourself. It's my understanding that they are not legal for automotive applications in many states (including NY, I assume, because just about everything is illegal there). I suspect you would have a problem getting a reputable shop to touch the system after it was converted.

I would recommend R-12, the only downside is the cost and it's really not that bad, maybe $150-200 for a charge.