A/C questions - PeachParts Mercedes-Benz Forum

Nate Stanley · #1 06-11-2002, 11:48 AM

To all,
The 1984 300D Turbi I bought in March had been converted to FRIGC FR-12, made by Pennziol in 1997 FRIGC has 69% R-134, 2% butane and the rest R-124. The compressor still turns, but I have zero low side pressure, and am faced with a flush and refill.

I have 3 questions for you-

1) have any of you had any conversions done with this refrigerant?

2) what were the long term effects on your cars?

3) this one's really got me stumped- where is the high side port supposed to be? I see a fitting on the passenger side of the top of receiver-dryer, but it's really hard to get to. A previous lister said it was on the condenser, but since this car was converted, I have no way of knowing if the port may have been moved from the stock location.

Please advise,

tcane · #2 06-11-2002, 02:05 PM

Nate:

FRIGC is an EPA approved replacement for R-12 (see an earlier recent post by me with all the EPA approved refrigerants and other info you should know). 2% Butane is not an issue regarding flammability, otherwise EPA would not allow its use in motor vehicles.

Did you use AC pressure gauges to find no low side pressure?

High pressure AC line is smaller in diameter than the low pressure line and runs from the AC compressor (located driver's side below the power steering pump) close to the bottom of the radiator to the drier receiver located in the right front of the engine compartment - at least that is where the high pressure line is on the ones I've seen. The high pressure fitting should be at the drier receiver, but it may be somewhere else like at the condensor - as you wrote, look to find it there should only be one fitting. Why do you want to access the high pressure line - to check for pressure to see if any gas remains? When the AC system is not running the pressure equalizes in both the low and high pressure lines and if there is a leak usually all gas is lost. One easy way to visually find leaks is to look for AC oil at the AC connections - won't work if you have a filthy engine because other leaks can look like AC oil or if you clean the engine the AC oil is gone. Otherwise, more technical diagnostics are needed using special tools to find the leaks.

My $0.02 worth.

Good Luck!
Tom

Nate Stanley · #3 06-11-2002, 02:16 PM

Tom,
I swapped the FRIGC fitting for a standard quick disconnect fitting before starting the engine and ran a gauge on the low side while the engine was running and the compressor was turning, and got zero PSI.

I was looking to see what the high side pressure was and to establish whether the tech that did the conversion had put a quick-disconnect fiting on the port. He did not.

Now that you verified where the high side port is, what I found there last night was a flimsy hex-shaped metal cap that had all but rusted off.

Removing the cap revealed a fitting that was still under some pressure when I loosened it a tad, but it looks like I'll have to depressurize the system and put a quick disconnect fitting on it at some point in order to monitor system pressures when I do the recharge.

BTW, I have done a successful R134 conversion on my F-250, and am not afraid of this project.

jcyuhn · #4 06-11-2002, 02:37 PM

I don't see any rationale for using FR-12. Since it's mostly R134a, it cools just like R134a (not so good...). Most shops won't service your car - they won't touch these blends. When it leaks, the different fractions leak at different rates, affecting the performance. Guess what I'm getting at is you should just perform a 134a conversion if you have to go into the system anyway.

On my 1984 300D the high side fitting was in the metal portion of the high side hose before it entered the condensor. As I recall, it snaked around the botton of the compressor, then the front of the oil pan, then up and over to the condensor. The high side fitting was kinda sorta on the passenger side of the oil pan. You had the crawl partway under the car to access it.

Seeing zero PSI on the low side with the compressor running indicates a severe undercharge - you have a leak somewhere. That the compressor runs at all indicates the cutoff switch - mounted on the receiver - is seeing at least 2 bar of pressure, so there is some refrigerant in the system.

Good luck.

Nate Stanley · #5 06-11-2002, 02:44 PM

JCYHUN,

Thanks for the detailed roadmap to the high side port! Looks like MB went to a great deal of trouble to hide that port. Maybe the same group did the oil cooler line routing--

I agree that either 134 or 12 (the good stuff) should be used, and since you need a license to purchase FRIGC, I'm going to go with a 134 retro. Since I live in a moderate climate, it should work OK.

tcane · #6 06-11-2002, 03:35 PM

Nate:

I agree with JCYHUN on using straight 134 since you can buy it anywhere without certification. And, where you live it will work OK - not in TX or other southern areas of the US.

When you said the compressor turns I thought you meant turned by hand. Are you saying the compressor turns with the engine running and the AC turned on? If this is so, then not only may you have a low pressure side leak, but also a clogged expansion valve is a possibility. A new expansion valve costs about $27 from Fast Lane.

Question - you wrote that you are not afraid of this project. Did I write something to imply you could not repair your system (other than the possible need for special diagnostic tools and related info that you may not have access to)? I was not implying you could not repair your AC system, only that at some point in diagnosing and fixing AC systems more specialized info and tools are needed and most people do not own or have access to - making further attempts to fix an AC problem more like replacing parts until the system works, not an efficient way and can be expensive for parts cost-wise and time-wise.

Good Luck!
Tom

Nate Stanley · #7 06-11-2002, 04:49 PM

Tom,
I certainy meant no offense by my comment-or to imply that you had cast aspersions on my ability, please accept my apologies if I offended you.

Previous inquiries about AC work on this forum have drawn (and with good reason) cautionary statements from professionals who want to ensure the safety of someone who might get in over their heads if they just started poking around a pressurized system.

All I was trying to do was make a general statement that I've had experience with charging AC systems, and that I was looking forward to the challenge of this one. I also have a friend who retired from the AC business that I can turn to if things get ugly.

Regards,

tcane · #8 06-11-2002, 06:24 PM

Nate:

LOL :p I thought that I had offended YOU! OK, we're both reading into this something that is clearly not there. This is a common problem when writing - writing with precision or nearly so and critically reading to avoid misunderstandings.

I agree 100% with what you and others have written regarding being carefull with AC systems because of the high pressure involved and also the very real chance for injury caused by the very cold temps from escaping refrigerant (even the short-term exposure when removing the fittings from gauges or refrigerant cylinders). Safety glasses and protective gloves are needed.

Having made a "few" posts like you and my professional experiences, I've seen way too many members/others trying to do fairly complicated repairs without a shop manual. Then an emergency plea/post for help bail to them out when the repair really becomes a problem. Surprisingly, many libraries have a wealth of very good info on M-B repairs (especially the Mitchell line of repair manuals) and most people do not even think to check the library or their ego is so big they think they can do the repair without a manual. Oh Well!

!

Glad to hear you have a pro to help if things get sticky. Most folks don't have anyone to turn to other than a repair shop (many who will add a premium for fixing a DIY screw-up).

Good Luck!
Tom