A/C recommendations for the MB vehicles - Page 13 - PeachParts Mercedes-Benz Forum

vstech · #**181** 10-14-2011, 01:09 PM

THANKS for the offer! your DIY's are legendary!
You will get all the help from me you need!
ok, yes mig gas is PERFECT for a flush agent.
I'd not use shop air for anything in an a/c system. the problem you run into is the moisture left in the lines will instantly ruin the desiccant in the receiver when you attach it. best to use dry gas 100% of the time.

as for the lower manifold, I'd replace it too. that way you don't have the corrosion gunk that's surely in the lines contaminating your oil, and you get fresh R12 fittings! because you WILL break the low pressure line fitting off when you attempt to remove the 134 adapters...

Quote:

Originally Posted by dieseldan44

OK, I read through the entire thread.

vstech and leathermang - I'll make you guys a deal - if you help me through my A/C 'rebuild' I'll document it all and write it up so it summarizes this thread into an article and DIY with FAQ's. You guys are warriors answering the same q's every year, so I want to make it easier for everyone in the future.

Normally, being in Boston, AC is not high on my list, but I have gotten so frustrated with no shops around here knowing what do on any A/C system, Id rather just buy the gear and do it myself.

I am rebuilding the 82 300D's AC. It is my fiances car and I want to hear complaints on how cold it is

- It had been converted to 134, but I would like to deconvert it to R12
- new evaporator already installed
- new condenser to be installed
- new compressor and o-ring kit from Carlisle in SA, TX is sitting at my feet
- new R/D purchased
- new expansion valve installed
- new upper manifold A/C hose. I'd like to re-use the lower manifold if possible.

tools i have acquired:
- robinair 2 stage 1.5 CFM vacuum pump
- R12 and R134a gauges
- A/C leak detector

I plan to in this order:

this fall:
- flush entire system and blow clean with dry shop air
- replace all o-rings using nylog sealant
- add 4 oz of mineral oil to compressor, 2 oz to evaporator, 2 oz to R/D
- pull vacuum for hours
- charge with 4 oz of R22 and inert gas (*) to check for leaks
next spring (car sleeps while salt is on road):
- re-evacuate, replace R/D, hold for an hour, then charge system with propane (j/k...seeing if you guys read this far) R12.

Questions for the experts -

(*) 1.) Can I use MIG welding gas (75% argon, 25% CO2) as my inert gas for the pressure test? I ask because I already have plenty of it.

2.) For the deconversion, I need to go back to R-12 fittings. How can I tell if I have damaged anything by taking the 134a fittings off? That isn't entirely clear.

3.) For the blowing out of the lines with air after the flush. If I use my air compressor with an inline desiccant and oil/water separator - is that OK? Even if there is a tiny amount of moisture that gets through, won't that boiled out during the vacuum step? (I could use welding gas here, but I don't want to waste it)

thanks, looking forward to learning to do this the right way...
dd

dieseldan44 · #**182** 10-14-2011, 02:33 PM

vstech -

great! looking forward to the collaboration.

i want to be clear on this (you said MIG gas is ok for flush, but not for test charging):

Can I use the MIG gas in place of Nitrogen for the 4oz of R22 test charge?

I ask because i know lots of people have access to MIG gas, and not many have easy access to pure nitrogen. i sure dont...id need to buy a cylinder.

vstech · #**183** 10-14-2011, 06:12 PM

the mig gas is perfect for both flushing and pressure testing.
nitrogen is CHEAPER than Ag/CO2, and it's moisture free. that's the only reason it's preferred.
I have started using Liquid CO2 supply as a flush gas, I've got this COOL little tank with a blow gun attachment. works great, and I charge it up at my Restaurant customers!!! FREE REFILLS!

leathermang · #**184** 10-14-2011, 11:00 PM

Are we just talking about using the liquid CO2 to push the liquid flush through the system..
or using the liquid CO2 as the flush liquid ?

vstech · #**185** 10-15-2011, 09:28 AM

oh, I'd not put the liquid into the lines, that could damage them! (-180F on rubber not a good thing!!!) but in liquid form, CO2 boils off like freon in the can, and the pressurized gas is perfect for pushing out the flush. it's also a good shield gas for welding!

do not invert the CO2 cylinder!!! DO NOT PUT LIQUID CO2 into your system!!! VERY VERY VERY VERY dangerous!!! 2000PSI is VERY VERY VERY BAD for any system!!! ONLY USE THE GAS for blowing out the lines!!! or REGULATED PRESSURE BELOW 200 psi to pressure test and mix with 4oz R22 for leak detection!

dieseldan44 · #**186** 10-15-2011, 11:58 AM

Quote:

Originally Posted by vstech

oh, I'd not put the liquid into the lines, that could damage them! (-180F on rubber not a good thing!!!) but in liquid form, CO2 boils off like freon in the can, and the pressurized gas is perfect for pushing out the flush. it's also a good shield gas for welding!

do not invert the CO2 cylinder!!! DO NOT PUT LIQUID CO2 into your system!!! VERY VERY VERY VERY dangerous!!! 2000PSI is VERY VERY VERY BAD for any system!!! ONLY USE THE GAS for blowing out the lines!!! or REGULATED PRESSURE BELOW 200 psi to pressure test and mix with 4oz R22 for leak detection!

OK - Im glad that is cleared up.

Another series of questions meant so that you guys answer it for a last time:

1.)What are acceptable flush solvents/fluids?

2.)Are one of the commercial preparations better than another?

3.)How much solvent should one expect to use to do a complete flush in an typical MB system?

leathermang · #**187** 10-15-2011, 12:44 PM

I am just going for the last one as a concept...
in the FSM for AC from MB....
they have a circulating machine with replaceable filters which ... well, lets go from another direction..

We ( or you either ) have no way to anticipate how much stuff is in your system that you do not want there...

You do not want to have it all apart doing it correctly.... then be chinchy with the CHEAP ( relative to the cost of parts or doing this all again ) flush liquid.

I suggest ( and I am not alone ) doing your flushing with at least two different batches of flush liquid.... you run the first one through.... if really bad looking change to cleaner fluid... if not so bad... run it through several times (FSM says both directions but specifies which direction first).... the best you can and do a flush with clean new fluid.... no need for one area to contaminate another...
IF there was any stage in this whole process where OCD or anal retentive is a good thing.. .this has to be it....(although all of AC work benefits from it )...
So how much is a quart of flush ? IF you had more than you thought was needed watching the exit fluid clarity...... I would use just put that through as a matter of " more is better ".....
So the answer is.... you won't really know until you get into the job... and if you can get your flush from a place close by... you just run get more when you see you are not going to have enough.... not everyone is lucky enough to be able to do that of course...

vstech · #**188** 10-15-2011, 08:32 PM

this is the reusable flush can I use...

the flush agent can be a quality designed chemical, about $40/quart, or some have used acetone as a fluid.
as long as it dissolves the oil and is TOTALLY removed, it's not critical what's used, but it's GOTTA all come out! it does help if the chemical you use is compatible with rubber automotive hoses!

dieseldan44 · #**189** 10-15-2011, 11:28 PM

OK, cool. Got it on flushing.

Next questions concerning R12 fittings for those de-converting....

vstech - you mentioned not being able to get the R134a fittings off the converted AC hoses. I have a new upper hose...fine there. However, a lower hose is ~$250 special order item.

Is there an alternative here? It seems silly to spend $250 to replace a hose just for the fitting...

vstech · #**190** 10-16-2011, 06:33 AM

you could try heating the fitting before trying to remove, but torches tend to melt aluminum... so, be careful. the problem is most conversion fittings have a green or red permanent locking compound on them. and when you remove the adapter, it tends to rip the fittings loose from the line.

dieseldan44 · #**191** 10-16-2011, 12:34 PM

I'll ask what is the first logical thought :-)

Other than illegality, couldn't I just leave the 134a fittings and charge with r12 anyways?

Assuming I dedicate a 134 gauge set to r12 and I mark it.

I know you guys are going to say not to do this...but other than the legal aspect, why is it a bad idea?

vstech · #**192** 10-17-2011, 12:42 PM

that will work fine, but YOU will be the only person who can work on the AC from then on...

leathermang · #**193** 10-17-2011, 02:52 PM

dieseldan44, since we talked on the phone the other day I know your name and phone number....
And you know I believe in following any reasonable rules which apply....
You really want me to know you have done this ?
LOL

leathermang · #**194** 10-17-2011, 02:58 PM

It is a bad idea because you could screw up someone's recovery machine by it not being identified correctly...... sorta of the Golden Rule....
Now tell us how this thought came to you ....Do you think it is going to be that hard changing it over to the proper fittings ?

dieseldan44 · #**195** 10-17-2011, 03:04 PM

Well the question had to be asked for the education of the community. I dont plan on doing this...I am going to try like heck to get my R134a fittings off without damage.

I think its important for the document I am preparing to have sort of a 'checklist' of parts and hazards for people who are new to A/C work must consider in a de-conversion to R12 on MB vehicles.

$250 is a lot of money for an AC hose, don't you gents agree?

Attached is a picture of R134A and R12 fittings to help identify what exactly is on the vehicle in question.

My AC gas leak detector came in today. $37 on ebay.