Air Conditioner r12 - r124a Conversion Catch-22 - Mercedes-Benz Forum
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post #1 of 27 (permalink) Old 05-13-2016, 07:17 PM Thread Starter
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Question Air Conditioner r12 - r124a Conversion Catch-22

Hello Everyone! Been lurking for a couple years - time for my first post.

I bought a 1984 300D Turbodiesel a little over a year ago. It's been great so far and I've been very happy with the purchase. Very solid cars - I even drove it from SoCal to Denver and back in the middle of August with no problems. 270,000 miles, with working windows, sunroof, dash lights, A/C and cruise control!

Except the A/C has lost much of its juice and doesn't blow very cold anymore and doesn't seem to work at all if it is much hotter that 90 F outside. So, I've been thinking about giving it a recharge now that summer is coming. Here's the problem:

Naturally, it came with r12 in 1984. I obtained service records from the seller and he had the A/C recharged in early 2014 and the invoice says r134. So, I thought it had been converted and I could start by just trying one of the spray cans you can get at the auto stores. Then I looked at the lower valve where it's supposed to be filled and it had the old r12 style threaded valve instead of the quick release on the r134 valves.

On my way home, I stopped at a radiator & A/C shop and asked whether he had any suggestions. When he learned that I still had a threaded valve, he refused to touch it until it had been converted because he no longer disposes of r12 and he said there was no way of knowing what was in my car since the old valve was on it.

I got home and called the mechanic I have the invoice from, from the prior owner (it's far from me - so not an option to go to that mechanic). I told him I have his invoice which says r134 and told him about the valve and asked if their was a typo on the invoice or if he put r134 in. He insisted he put in r134 since it was in 2014. I asked how without a conversion and he told me that he has an adapter fitting which allowed him to recharge the old-style valve with r134. Overall, he sounded a little shady and didn't speak English that well, so I gave up on getting more info out of him.

I'd rather not pay for a conversion on a car this old and funds are tight now for me. So what do you guys think? Could it be true that it was never converted, yet filled with r134? If so, where can I get an adapter for the fitting to put r134 in the old valves?

Or, do you think it still could have some r12 in there? How do I get mechanics to work on it if they are afraid that it has r12 in it?

Thanks!
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post #2 of 27 (permalink) Old 05-13-2016, 07:44 PM Thread Starter
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Dammit! My first post and I missed a typo in the thread title (r134, not r124).

Sorry. This is the only forum I'm on that doesn't allow editing - guess I'm going to learn to get it right the first time . . .
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post #3 of 27 (permalink) Old 05-13-2016, 10:05 PM
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AC is one of the areas on this car where you can get into some repairs that are outside of DIY territory. I would highly recommend you only put R12 in UNTIL you have read all of the risks and conversion details. There are shops that run R12 still -- quite a few of them if you call around. There are a bunch of AC parts that are getting to be unobtainable with OEM and questionable with Chinese replacements. If I were you and your stock system works, I would try to hold onto it as long as you can.

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post #4 of 27 (permalink) Old 05-14-2016, 12:03 AM
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Converting an AC system to R134a could technically only be screwing on a conversion schrader valve. It could be very possible the shop temporarily used a R134a schrader valve to recharge the system and then removed it once they were done. That is literally all you need to put 134a into the system. That doesn't necessarily mean it's going to work efficiently and last a long time. Converting the system properly usually means finding a compressor that is designed for R134a, changing out condensers etc. I would take it to a shop to evacuate the system that is okay with disposing of R12. After that, its your call on what to do next.
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post #5 of 27 (permalink) Old 05-14-2016, 01:36 AM Thread Starter
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Yeah, I really don't want to pay for a r134 conversion because of the cost. Maybe if I could find an adapter, I'd try to shoot some in, but I know that most shops will insist on doing a full flush, replace some of the parts like the dryer, a leak check, etc. before they'll put the r134 in.

I might shop around and see if I can find a mechanic who is willing to give a recharge of r12 without the leak inspection first (with a car this old, I'm sure they'll find something and the costs will skyrocket) before taking more expensive tests. Since it hasn't been converted, the r12 is better for the system because of the lubrication. Though, the mechanic I talked to today said that r12 is $130/pound around here, so I guess nothing will be cheap.

I just wish I could know what has been done to it in the past. If they did charge it with r134 in 2014, I don't know if they flushed the r12 or just added to it. Also, I thought r134 required some type of mineral oil additive to help with lubrication and I don't know if they did that or not.
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post #6 of 27 (permalink) Old 05-14-2016, 08:22 AM
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R134 uses PAG oil. It's a type of glycol. R12 uses mineral oil. To convert from one to the other you need to flush the old oil completely out. They do not mix.

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post #7 of 27 (permalink) Old 05-14-2016, 10:29 AM
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Just know that if you half ass it, you're not going to get a good working AC that will last for very long. In order to do it correctly you need to flush the system thoroughly, check for leaks, replace the expansion valve, replace all o rings, recharge with correct oil amount. It's not going to be worth half assing it and having a working AC for 3 months, and then your compressor failing.
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post #8 of 27 (permalink) Old 05-14-2016, 05:38 PM
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Anything you do that isn't a full refurb (minus a new compressor if yours is still working) will result in poor performance and short life. Not worth it.

As it stands, if you just shoot either R12 or R134a straight in without knowing what is in it now it'll be a gamble. There are universal oils, but they are expensive, so the odds are a non-universal oil was used and there is a chance things won't mix and you'll totally toast your A/C system.

With your A/C compressor still working the odds are pretty good you can DIY this if you're good with a wrench. It's not complicated, just hard work. You'll need to replace the dryer ($20ish) the expansion valve ($20ish) all the o-rings ($10) and flush it well with several cans of flush ($30ish). You'll also have to invest in a set of gauges and a vacuum pump, which you can get for about $100 combined at harbor freight. Then you can fill it with whatever refrigerant you want - know that without changing the condensor R134a will not work that well above 90*F anyway even with a fresh fill...

Ask any specific questions you have, but that's the best route.
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post #9 of 27 (permalink) Old 05-15-2016, 03:27 PM
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Quote:
Originally Posted by BayouFlyFisher View Post
R134 uses PAG oil. It's a type of glycol. R12 uses mineral oil. To convert from one to the other you need to flush the old oil completely out. They do not mix.

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+1

Every older MB that I purchase is immediately converted back to R12 if need be.
I'm on the Gulf Coast and in our part of the country, we battle 100+ degree temperatures and 110% humidity- the r134 simply does not cut it. The cars absolutely do not cool at idle on 134. You're in S CA, so you can probably get by with 134 if that's what you have. Mind the oils as stated above.

Of course, it all depends on temp preference as well. I want the car so frigid the windows fog....
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post #10 of 27 (permalink) Old 05-17-2016, 06:17 PM Thread Starter
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Thanks everyone for the advice so far. It sounds like the only way to do it right is pretty much a full conversion. It makes no sense to do all of that work and then re-install a 32 year old compressor and dryer, which aren't very good quality to begin with. I still can't afford that, so it's not an option.

After so more research, I found out r12 is still legal in Mexico. I live less than an hour from the border, so I'll probably go there to get the job done right.

Any SoCal people here who can recommend a Tijuana shop? There are a few that look good on yelp, but it'd be nice to hear some personal experience.
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