Mercedes 240D Air conditioner refill with Air Duster write up - PeachParts Mercedes-Benz Forum

ASteele · #1 09-12-2020, 12:59 AM

Hello everyone this thread is for everyone trying to fix their original air conditioning systems in their old Mercedes that run r12 refrigerant. Before I start talking about the AC job me and my father completed, I want to go over the history of the car. "Zelda" is my 1983 Mercedes Benz 240d, we got the car back in 2013 from a family member and it was her first vehicle. The car was an automatic with an om616 and was purchased in Florida from a Mercedes dealer. The history of the existing A/C system is that it was probably never used. The family member who owned the car, upon being asked why she never used the A/C was, "I either could have power or be comfortable, I chose power". So, upon starting this project it was assumed that all A/C system components where star marked and original to the vehicle. She used the car probably until the '90s at most and it sat around collecting dust in her driveway. years later in 2013 instead of taking it to the junkyard, she gave it to me and my father and over time we have fixed it up. The car has done multiple trips to Michigan from Maryland and has rarely ever broken down and just like a w123 that is cared for its usually something minor. The car got its name Zelda from me and my brothers deciding to call it that because we play the popular videogame "The Legend Of Zelda" Long story short just 2 years ago the automatic trans blew apart and it was my brother's beater car to college so he got another vehicle in the meantime. Our buddy called us up when his engine blew up and said come get my manual and swap it in your 240d and keep her going. So after a road trip last April we got the parts and by early October and a lot of headaches later the car was successfully manual swapped and its a hell of a lot more fun to drive. Since the car had more power since it was a stick now we decided to restore the AC since it can get very hot in the Maryland summers.

Now that the history of the vehicle is out of the way I want to emphatically state that the AC system is all original OEM from Mercedes, nothing was changed at all except for the rubber O-rings in the system. Just have to stress that since I know some people will try to argue I'm wrong. Moving on you may be asking how in the world I'm going to recharge my almost 40 yr old AC system if the refrigerant is not made anymore. Yes R12 is not sold residentially anymore and you need a license to buy it now however there are substitutes! No I'm not talking about frosty cool or other nonsense I'm talking about r-152a or HFC 152a This stuff is basically r12 and it's in the computer air dusters for households. Yes, that's right your buying an r12 substitute and cleaning your electronics with it and the EPA hasn't banned it. R-152a (1,1-Difluroethane) - This is a fascinating material that is a potential replacement for 134a when that is ultimately phased out. Amazingly, this product is what is contained in dusters as well. In fact, a quick YouTube search for "Duster as Refrigerant" will yield some fascinating videos about how to charge an A/C system with duster propellant. And for reference R12 is Dichlorodifluoromethane Now as stated previously there are multiple videos on youtube of people recharging AC systems with r152a and its not any different than charging the system with traditional freon. Also, this stuff does not have the higher head pressure problems r 134a does and r152a does not need a parallel flow condenser to produce r12 results. R134a requires a parallel flow condenser, whereas r12 and r152a only require a single flow condenser.

Let's review the step by step procedures on how to do this:

The first step was to see if there was any residual charge left in the system. We connected up the manifold set and got "0" for a low-pressure reading. Based on the no-charge another set of assumptions was made.

PREPARATIONS:

1st) Vacuum down the system and see what your working with.
2nd) See if it holds a vacuum for a few hours.
3rd) Apply air pressure about 60 to 80 psi depending on ambient temperature and see how long it holds. This not only tested the existing seals but also the initial condition of the components. That is compressor, condenser, dryer, evaporator, and expansion valve. All connections were tested with a soap/water solution through a spray bottle to test for any leaks.
4rth) replaced all O-rings in the system at every connection including the manifold plate on the compressor.
5th) was to place a nitrogen charge on the system and see if any leaks. This would have been a great test but we didn't have access to a nitrogen bottle and had to do the test with compressed air. Again charging to 60 to 80 psi depending on air temps.
6th) If all the above test proved valid, then we planned to re-vacuum the system. Doing a deep vacuum for approx 6 hours. Doing this for an extended length of time it sucked all the moisture or a good portion any existing moisture left from over 30 years and two, it brought it down to 30 inches of mercury.
7) Once the 30 Hg was obtained as indicated on the manifold gauge, we turned the air pump off, closed the low-pressure valve on the manifold, and left it for 3 days. As stated earlier, we should have charged with nitrogen but didn't have access to anybody with a spare tank for use to use.
We made sure that the air duster cans stated that it contained 152A refrigerant. Without the component in the air duster can, this whole project would not have worked.

CHARGING THE SYSTEM:
Using the tool to side puncturing the air duster cans, the refrigerant was applied through the low-pressure line. Slowly the clutch on the compressor kicked when the pressure switch activated after seeing 29 psi of pressure.
According to the research, the amount of air duster required only needs to be about 1/2 that of the R12 requirement. Since about 2.6 lbs (40 oz.) of R12 is required for the existing system it appears that 20 oz of air duster achieved the same results as shown in the pics.

The achieved observed results are, cold air was pouring out the air vents, condensation was forming on the windshield while test driving the vehicle, the air conditioning lines had moisture on them, the aux fan came on at the specified temp of 126-127 Fahrenheit, and all of this was achieved using existing 40-year-old original components. Nothing has been changed except the O-rings.

NOTES:

Before I leave I wanted to help shed some light on how 'piss poor' the AC will be with an r134a set up and the original equipment that came from Mercedes. For a proper r134a conversion you need to evacuate the whole system, replace every seal in the system, replace the Schraeder valves, drain the compressor of oil and replace it with PAG or Ester and flush every line of the system with compressed air and kerosene to clean the system of r 12 and mineral oil residue. Doing all of this will give you ok Ac at the most, the problem with r134a is that it runs higher head pressure and a single flow condenser cannot accommodate the surface area needed to cool it properly to give you ice cold AC, thus a parallel flow condenser is needed. That's why people who completely replace everything with a Sanden AC system the kit comes with a parallel flow condenser and you have to make the existing lines fit into it..... yeah not very user-friendly. Without a parallel flow condenser your only going to run 20 degrees cooler on a hot day. Whereas an R12 system would not be missing a beat and be delivering 40+ degree colder air on a hot summers day. Also, another note ensure that your Auxiliary cooling fan is operational since it is necessary on hot summer days when the system is working very hard. The fan switch on the side of the drier closes at 126-127 degrees F and that's the high side of the AC system where all the heat is. If someone wants to fully explain the operation of the Aux fan you're more than welcome too! This is why so many people on the forums encourage others to stick with r12 if possible and to never retrofit it because the results are very lackluster and if you want to you can always purchase r12 off eBay and throw it in the system also just make sure you have no leaks beforehand otherwise you'll probably cry from the money you just wasted

We tested the system with a meat thermometer and we got down to 40 degrees F in our driveway at idle. Don't have pictures of the thermometer on a road test yet but it does get down to 38 F at most and its blowing ice cubes so I'm happy.

IMPORTANT:
the fuse for the aux fan is a 16amp red fuse and the aux fan draws about 20amps so I upgraded the fuse to a blue 25 amp fuse and I have not had a problem yet. You're also going to have to get a can clamp to recharge the AC system so you can puncture the refrigerant or substitute can

Any questions and comments appreciated

You can use the shared link below to view a public google drive folder with all the pictures we have (sadly we did not have pictures of the vacuuming process or O-ring install but those are very straightforward.)

Link to pictures:
https://drive.google.com/drive/folders/1UmDcUx27SXgSk959dxUh5GiHyyqqyA5e?usp=sharing

cfh · #2 09-12-2020, 01:33 AM

What kind of oil did you use, and how much?

1983 300CD · #3 09-12-2020, 08:19 AM

Yes I did this last year! The cheapest cans were the Staples brand air duster from either fleabay or blamazon. 152a works well. I used POE oil based on a miscibility chart that indicated it mixes with R12, R134a and R152a. That way I felt I was covered if I didn't get every single speck of the 134a out of the system.

One of the tough parts about 134 is the pressure is so much higher. I've heard of the damn seals on the evaporator(remove the console and dash to fix it) leaking after adding 134 to one of these aged systems. Even if I had a Sanden I still wouldn't run 134 just because literally everything else works better with less effort/mods/expense. A Sanden would be for reliability. Focus on the refrigerant for cooling performance.

I also did the 152a before I had clarity about the use of R12. R12 is still superior but people hesitate to use it due to either cost($2.75 oz average x 41.8? ounces) or they are relying on bad info regarding the EPA regs. If you read the EPA regs the only thing that became illegal about R12 was making more of it or importing more of it. That's it. Same regs apply otherwise. On top of that the EPA specifically removed all licensing regs for DIY car owners. It actually says "DIY" in the language. Meanwhile alot of people have the direct opposite information. The only requirement they made is a DIY can't buy R12 in containers larger than 2lbs each. That makes sense to an extent. Buying 30lb tanks of R12 suggests it's more than just DIY. I can live with that. So at some point I will get a new drier, some wax free mineral oil, and a few cans of R12 and go back to the future.

It does start to seem like a bit of a revenue/licensing hustle when shops are so highly regulated yet there are air duster cans of 152a and even 134a that are sold by the pallet load and dumped out on keyboards across America.

ASteele · #4 09-12-2020, 09:49 AM

Quote:

Originally Posted by cfh

What kind of oil did you use, and how much?

We never added any oil because all the original oil was still in the system when we began this project. The compressor sticker on the GM R4 compressor states it takes 6 oz of mineral oil. Only use Mineral oil or Ester oil as the lubricant in an r12 AC system

Diseasel300 · #5 09-12-2020, 11:19 AM

It's extremely important to note that if the expansion valve has been replaced within the last 2 decades it will be orificed for R134a and performance when running R152a will be HORRIBLE. If you aren't running the original R12 expansion valve, dont' waste your time with R152a, it will perform WORSE than R134a! Been there, done that, confirmed across several MB and BMW cars.

The R134a expansion valves have a stronger spring and a smaller orifice to run a smaller quantity of gas at higher pressure than R12. When running R152a on these valves that results in a starved evaporator and 65-70F vent temps at idle as the best you will EVER see.

R152a works fine in a car fitted with the original R12 expansion valve though. Just stuff to keep in mind. If your expansion valve is seized, clogged, or dead and you have to replace it, do a full R134a conversion.

resago2000 · #6 09-12-2020, 01:14 PM

134 and 152 are both hfc and require the same type oil. I don't think mineral oil is compatible.
you should also replace the drier, to both get a clean system and oil accumulates there as well.

interesting about the TXV, where can you buy a TXV for R-12?
since the molecules for R-12,134,152 are smaller than each other respectively, I thought a TXV for 134 would be fine. hmmm..

ASteele · #7 09-12-2020, 03:13 PM

I am curious where can you get an r12 rated expansion valve for these cars besides the junkyard? and what makes the new r134a expansion valves different from the originals. Most importantly is it possible to modify a new r134a valve to be compatible with an r12 system? thoughts appreciated!

resago2000 · #8 09-12-2020, 05:54 PM

well, I just finished my 240D AC project. I have a new 134 TXV.
seems fine. maybe it would be colder with a different TXV, but its blowing cold enough. so I'm happy.
yes, I filled with 152a, and used the pressure method to fill, IE, get it to a stable pressure, keep an eye on the high side for fast increase.
my pressures stabilized at 50/200. I didn't totally fill the system, because my high side stabilized and didn't move for at least half a can (5oz).
when rev'd, high side is 250. it was about 90*F outside.

Diseasel300 · #9 09-12-2020, 09:08 PM

Quote:

Originally Posted by ASteele

I am curious where can you get an r12 rated expansion valve for these cars besides the junkyard? and what makes the new r134a expansion valves different from the originals. Most importantly is it possible to modify a new r134a valve to be compatible with an r12 system? thoughts appreciated!

R134a has a different molecule size and slightly different pressures than R12. The newer expansion valves have a smaller orifice and a different powerhead setup designed to work with the newer gas. You can't modify it to work with R12, your only source for an R12 valve is a pre-1993 car.

FWIW, a properly converted system running the correct expansion valve and with adequate condenser can blow nearly as cold as R12. My 1991 350SD with its original system (dual-circuit small-tube condenser) and the updated expansion valve will blow mid-low 40s on max fan in 100+ temps.

1983 300CD · #10 09-16-2020, 03:58 AM

The last TXV I bought was German and indicated R12 and R134, which is clearly not optimim. You can certainly chase a vintage functioning R12 TXV or just get a modern one like this one and keep moving. Yes you can make 134 act similar to R12 in an R12 system. It's a matter of what you feel like doing. If you don't feel like replacing the condenser and the aux fan and flushing the system to end up getting close to R12 then just put R12 in your R12 system and move on.

resago2000 · #11 09-24-2020, 01:24 PM

Given this info about the TXV, I thought maybe the txv was allowing too much refrigerant R152a through since it was setup for R134, R152 is smaller, so more would be passing through. My low side wasn't going below 50psi so wasn't getting great temps.

the red dot txv I bought is adjustable, so I tightened it 1/4 turn.
it made an instant improvement to psi and temps. I might give it another 1/4 turn, but as of now, the ac knob now works as it should, before, the only time it would cut out the compressor is if I had it just barely on, now it will cut on and off up to 60% and a little beyond.

I've been reading about superheat and subcooling, so will get a temp set to measure this and further tweak.

but if you are having some trouble getting r152 to cool like it should, try adjusting the txv 1/4 to 1/2 turn clockwise.
Just make sure you have your gauges hooked up so you can watch the pressures and temps.

Diseasel300 · #12 09-24-2020, 01:58 PM

Quote:

Originally Posted by resago2000

I've been reading about superheat and subcooling, so will get a temp set to measure this and further tweak.

but if you are having some trouble getting r152 to cool like it should, try adjusting the txv 1/4 to 1/2 turn clockwise.
Just make sure you have your gauges hooked up so you can watch the pressures and temps.

Careful with superheat and sub cooling, it will vary with engine RPM and load on the system. Typically automotive systems run anywhere from 3-5˚ superheat and around 20-30˚ sub cooling at full load. It's easier to charge by temperature differential. Your system is at a perfect critical charge when the temperature drop across the condenser matches that of the evaporator air temp differential. Typically 30˚F or so, meaning you have a difference of 30˚F line temperature (inlet vs outlet) at the condenser and a difference of 30˚F air temp (inlet vs outlet) at the evaporator. Note that the temperature method is only valid if the system is at full load (all doors open, fan on max speed, temp dial as cold as it will go) and ambient temperatures are 80˚F or higher.

It's worth mentioning that most TXV's are not adjustable, they're set at the factory for the gas they're designed to run.

resago2000 · #13 09-24-2020, 03:31 PM

I've got this one: RD-5-6868-0 Red Dot Expansion Valve

vwnate1 · #14 10-12-2022, 08:40 PM

Two years later, does it still blow cold ? .

resago2000 · #15 04-20-2023, 03:31 PM

yes, but I need to recharge every season. I left some original hose in the system that is apparently leaking.
I'm going to put a small heat exchange block hugging the high and low side junctions a foot beyond the firewall to see if it makes any temp difference.
I forget what its called - (IHX) - edited - , I researched it a couple years ago, and when I cut the hoses, I'll take the opportunity to install it.
its supposed to cool the high side slightly by using unused cold refrigerant as it leaves the evaporator and heads to the pump.
side effects will be slightly higher temps at the condenser.

I put 152a in my prius and is blows freezing cold air.