A/C recommendations for the MB vehicles - Page 3 - PeachParts Mercedes-Benz Forum

leathermang · #1 04-16-2011, 12:45 PM

29.9 is not perfect....
the barometric pressure varies....and 2 niner niner 2 is the reading on a ' standard ' day... at sea level at a specified temperature...
So perfect on any given day has lots of variables to factor in... but most techs have a reading on their machine which they quit once reached...
Vstech is referring to the fact that our AC's have a controlled leak at the compressor.. for lubricating the compressor front bearing.. making this NOT a Hermetically sealed system the way a refrigerator or your home AC system is... the compressor sitting in oil and all the lines soldered or the like...
I do not know if Manual Life has these answers to give us.... or even if he can get them from his friend... it is a good chance to go over some of the basics though...important basics...

Yak · #2 04-16-2011, 01:21 PM

Quote:

Originally Posted by Manual Life

84 300D

After a year and a half I finally got around to charging my A/C. It's so nice to have it and enjoy the quiet of windows up.

And, I assume if I doubled up on the fans for the condenser I would have cool air full time. As it is it warms up a little at idle and I am thinking this is the result of switching from R-12 to 134.

If that's not the problem let me know and what I can do. If it is the problem has anyone doubled up on fans? If so which fans?

Otherwise it works very well. I am happy to see how cold it is. I heard rumors that even a good a/c system didn't get very cold on these old cars.

I'm assuming this is still the original question.

It sounds like your system is operating normally with/without R-12 and you're considering options to make it better.

Yes, going back to R-12 would help. But as you've possibly already experienced it's not straightforward to source R-12. You can buy it on e-bay, craigslist, etc, but caveat emptor. If may say R-12 but be some variation with 12 in its name. You may be able to buy real authentic R-12 in some autoparts stores locally but you're supposed to have the EPA certificate. Purportedly easy to get online for minimum cost. You'd need to flush the system to get incompatible oils out, then re-charge after proper leak testing (vacuum as a rough test, then pressure as a final check - my system held vacuum, but leaked under pressure so I'll vote for a pressure test prior to installing hard-to-source R-12). I tried 3 shops in San Antonio (including Carlisle) and none of them wanted to put R-12 into my car.

Adding smaller diameter fans to a 134 conversion might help if it increased the volume of air across the condensor. This is probably a last ditch band-aid attempt.

Cleaning the existing evaporator of dust/crud might help since you'll get better airflow across the cool surface. There are posts on how to do this.

Modifying the vent flaps to do "re-circ only" might help since you're cooling previously cooled air.

Making sure the radiator and condensor fins are clean/clear might help (a swarm of monarchs or snouts in Texas will clog that pretty quick).

Since A/C feel is sort of subjective, I'd recommend putting a thermometer in your driver's side vent and finding out what the output temps are (low cost, no-tech meat-thermometer style available at Autozone or elsewhere is fine). Nothing appeases the opinionated A/C crowd like numbers and data. That way you'll have a reference of how good your current cooling is and what temps you might expect.

vstech · #3 04-16-2011, 01:26 PM

all NAPA stores stock R12 in cans. you need the cert 408 I believe, but it is easy to get online... open book test. for like 15.00
the cans are pricey, at like 25.00 each retail, if you run a shop you should not be getting cans, you should be getting drums... around $500 new.
and getting a sealed cylinder of 12 from craigslist is even cheaper... I've gotten them for free, to $100 or so for 30 POUNDS of 12...

vstech · #4 04-16-2011, 01:29 PM

Quote:

Originally Posted by leathermang

"I'm assuming this is still the original question." --YAK

Not really... this thread has been designated a sticky to become a standard reference guide...
So your input on anything you think should be addressed is welcome.... you do not have to limit your replies to the original OP question....
And you are doing a great job !!!

yeah everybody post all the questions and info on here you want. I'm going to try and organize the answers, and weed out the problem info. I'll also answer questions, anybody else answering questions please quote the post you are answering.

this is looking like a great start to the reference, and I'll devote a lot of time to it. (it's my field)

vstech · #5 04-16-2011, 08:09 PM

the fittings on some conversions can be removed, but it's impossible to know which ones can and which ones can't... better safe than destroyed...

francotirador · #6 04-19-2011, 04:06 PM

Quote:

Originally Posted by vstech

the fittings on some conversions can be removed, but it's impossible to know which ones can and which ones can't... better safe than destroyed...

Well, I'm still trying to understand exactly what I can do with the 134 fittings. Both high and low side 134 fittings were installed in my car when the R12 to R134 conversion was done. I want to change those fittings back for use with R12. Can I just get new Schrader valve inserts and the correct cap for R12, or is there more to the fittings than that?

Also, I see kits available with all of the green o-rings/seals for conversion to 134 from R12. However, I haven't seen any for reverting to R12 from 134. Does anyone know if and where they're available?

I really want to get this project done as the 134 just isn't cutting it in this South Florida heat.

I've ordered a new compressor, new drier, new expansion valve and new manifold hose. I have an R134/R12 Recovery/Recharge unit and 20 pounds of R12. So, I'm good on that front.

All help is greatly appreciated.

Hit Man X · #7 04-17-2011, 12:20 AM

Regarding the nitrogen test...

is one to have the system oiled or not? Seems to me not as when you evacuate it you would lose some oil.

If no oil, do you simply evacuate the nitrogen then open one fitting to add the oil... then close it back up and vacuum down?

Perhaps it has been covered and I am just missing something. It is late and I am sleepy again

vstech · #8 04-17-2011, 12:53 AM

evacuation should not remove much oil at all... RECLAIMING will remove a significant amount of oil, but the reclaiming machine should separate and store the oil removed separately.
an existing system after evacuation, to test for leaks, with dry gas, and trace R22 oil should not be an issue.
fresh flushed system, may need oil for maximum leak free, but there's no good way to distribute the oil without a full charge of refrigerant... so it's not important for spotting leaks.

vstech · #9 04-17-2011, 09:09 AM

Quote:

Originally Posted by leathermang

The MB AC FSM suggests as you put the system together... spacing out the total oil you are going to use in several places.... so that the entire burden of getting it spread around is not borne by the refrigerant..
This is ESPECIALLY IMPORTANT ON SYSTEMS USING THE R4 Delco since it is totally dependent on refrigerant carried lubricant.... lacking an oil sump itself..unlike most other AC compressor models ... even earlier models like the York..

yup. this will certainly aid the distribution of the oil into the system, but!!! it will not flow in nitrogen, so it will not coat all the seals and surfaces of the lines etc without the refrigerant charge.
my point here is on the OP's statement of his system not holding vacuum until the oil got into the system,,, it's not important for a pressure test. it is CERTAINLY important to have the exact volume of oil, distributed during installation of the components in the quantities specified in the FSM.

vstech · #10 04-18-2011, 06:04 PM

Quote:

Originally Posted by Hit Man X

Hmm, so do I just vent the Nitrogen? Then carry on the charging process as normal?

yes.
after verifying no leaks are present, vent the nitrogen, then attach your vacuum pump, and evacuate the charge, and refill with the correct volume of refrigerant.
I use 30 lb jugs, of refrigerant, so I can charge with the system OFF, the correct volume into an evacuated system.
most DIY types need to use 12 oz cans, and each time the can is opened, air gets into the manifold, and the car, and some of the refrigerant is lost.

to properly recharge a system, a reclaimer is needed, and a charging station, or at least a jug of liquid refrigerant, and a scale...

leathermang · #11 04-17-2011, 11:27 AM

I do not think the oil for the compressor is or should have to be counted on to seal the system.... as NYLOG of the proper color would be used on the o-rings and gaskets as the system is put together..
So the nitrogen would be used with the oil already in and spread out ..... do nothing except provide pressure and a SNIFFABLE refrigerant ( R22) to use as leak detection...
The compressor is not going to be used until the system is certified leak free...and the proper refrigerant is installed... so that can be used to carry the lube around and keep the compressor lubricated.

colincoon · #12 04-17-2011, 01:15 PM

So far this is what I have gathered as the correct "process" of refilling the system after rebuilding it. This is assuming you have replaced all the o-rings, parts, etc.

1. Add oil to the system in various spots so that it is easier on the system to circulate.

2. Add PRESSURE to the system to check for leaks, etc. with 4oz R22 in, CO2, or Dry Nitrogen.

3. Once pressure has been added and no leaks detected, vacuum down the system to remove moisture.

4. Add freon of the proper amount to the system and "pulse" the compressor to get it circulating.

Is this correct?

Also I'd love to see opinions on different compressors and what makes certain R4's different from others and what the CORRECT R4 compressor for our car is.

leathermang · #13 04-17-2011, 01:36 PM

I have not seen any instructions concerning " pulsing' the compressor...
I think once you are ready.. you install all the refrigerant which will do naturally..with warm water at the base if using a small can.... figuring that you will get enough in to activate the low pressure cut off switch... otherwise it would need to be jumped to use the compressor to help load the system.... .. with the windows down, system on HIGH COLD... and put the refrigerant in... in the form of VAPOR... not LIQUID ( unless you really know what you are doing .. otherwise you can crack the reed valves in that new compressor... or an old good one for that matter )...forceD air blowing into the condensor... etc... like Vstech mentioned above...

amosfella · #14 04-17-2011, 02:16 PM

on a 95 S320, I"m curious what other refrigerants could be used. The r134 doesn't really cut it. I had converted R12a a while back, and it held for 3 years under extreem temp variations...
I"m thinking about taking the system apart and checking it. Could argon be used instead of co2 or N??
I"m in Canada and R12 is a huge no no... What other refrigerants would be good to use?? Even when the R134 was working 'properly' according to the tech, it still didn't cool the car worth a damn...
BTW, window tinting is illegal here unless it's factory tinted glass. Car is a gold color with mushroom interior....

leathermang · #15 04-17-2011, 02:40 PM

Yes, Argon is fine to use.
I do not recommend any except R12 or R134a for several reasons...
I suggest that you first be sure your system is in good shape.. have you cleaned your evaporator fins ? This is something seldom done and sometimes not fun or easy... but very very important... if they are clogged up with whatever.. you are not getting good air flow over those cold fins.... so your air can not be cold in the car...
Then... your condensor... the bottle neck of all AC systems... think about upgrading the fan and being sure your fins on it and the radiator behind it all straight and clean..
Those would be the most important and effective things to start with... and assume they will allow the R134a to do what you need for cooling...
I have three autos with R134a here in the middle of Texas... and in a humid spot to boot.... and they all do just fine...
Be sure your basics are up to par before considering going to some off the wall refrigerant.....