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First off thank you for closing up the thread! Always good to hear the end result. In my expiration on many of my personal cars converting to 134a I would not replace orings unless they were leaking. I would install the updated service valves and inject Ester oil which is compatible with both r12 and 134 and charge to 80-90% of the system capacity. Normally I never had any issues doing this. When it came to a clients vehicle in the shop it was prefered to do a new compressor and drier, valves and a new orifice tube or expansion valve or the like. Flush the system and charge. Some people who wanted the budget approach we would drain the compressor as best possible and use ester oil, and really it would work for a long time with minimal issues. It really depends on the car, and what components the system has. At the shop it was usually a system that was very old and and been dormant for a long time due to a compressor failure or the like, so it wasnt a slap together repair.

GM used an orifice tube that is easy to replace and they are available for the 134 change over, that would help with much of the cooling issues. Early cars that had POA valves and whatnot you could adjust to get proper pressures. Many of the lack of cooling issues ive found is due to the condenser. In the w126 cars they were not very efficient with using 134, and an upgrade to an new aluminum condenser from the old school copper/brass condenser really waked the system up with the conversion is done. Some cars like my 82 oldsmobile have such a big condenser its not an issue with 134 and the temps at idle will still get into the 30s. Some cars you just need more airflow at slow speeds, so having the fans come on or adding one makes a huge difference. Its all vehicle dependent.

But in the long run you can get away with ester oil, 134 valves and a proper charge without any issues, performance will just vary.
 

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Its been a while, but i want to close the loop here.

I eventually got the system vacuumed out at a shop. There was almost no remaining R12, however it appeared that the compressor & clutch were functioning and it held vacuum!

I decided to move forward with the R12 recharge and completed that a week or two ago. The A/C works perfectly and, as others have stated, when the car is running down the highway the A/C will freeze you out.

One item of contention that I had with the mechanic and wanted to get people's take on here was his statement as follows:

"Back a few years ago, it was recommended to replace all the o-rings, the compressor, the oil, the expansion valve, the drier, and the service valves for a R134 conversion, but what we recommended now is to just replace the service valves and put R134 in there and you'll be good to go." -Mechanic

Obviously the expansion valve and system won't be as efficient as R12, but can you really expect success leaving the o-rings, drier, and old oil in there and pumping in R134?

Everything i've read on here has stated that the o-rings required for R134 are different(higher pressure), the oils are not compatible, and that any conversion should also include a drier.
I disagree. Dumb mechanic or malicious one.

The black R12 o-rings needs to be replaced with the modern green R134a o-rings.

The R12 optimized expansion valve needs to be replaced with a R134a optimized expansion valve.

The R12 pressure switch needs to be replaced with a R134a pressure switch because they switch at different pressures.

System needs to be flushed out and PAG46 oil installed.

I replaced the entire system except the condenser, evaporator and hoses with 4Seasons R134a components and it's just as freezing cold going down the highway as it was with R12. Only difference is not as cold sitting in traffic, which I may try bypassing the low speed resistor on the electric fan to help with that.
 

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I know this is the W124 forum, but the mechanics are the similar... For a conversion, the TXV, accumulator/dehydrator, o-rings (at least as many as you can get to) should be replaced as well as using a couple cans of flush and new PAG oil. I just did this to the 1982 240D and the A/C works great. I used the write up on DieselGiant as a rough guide:

How to Repair Your A

I have a set of A/C gauges and a vacuum pump and I was able to determine the compressor was at least able to make pressure... the high side was too high and the low side was too low which told me there was a high side blockage (likely the filter/dehydrator). Once the system was opened and flushed, I could easily turn the compressor by hand, so I went with the existing R4 compressor (which had been renewed in the past). There was only one line I couldn't crack loose (the large comp. suction line), so that was the only o-ring I didn't change. Once flushed and back together it held good vacuum, so I charged it with 2-1/4 cans of 134a. The most troublesome part was researching/deciding whether to remove the existing (R12) schrader valves, which I did for the suction side and not for the high side.
 

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Thats completely wrong -- the oil does not mix and not changing out the drier is asking for trouble.

Replacing the o-rings is just for good measure so you don't end up having it leak out an old o-ring wasting money.
 

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Discussion Starter #25
Thanks for all the comments regarding the AC. It seems as though a very large majority of people think his advice is poor.

That just goes to show you why we do our own research.

Thanks to all.
 
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