DIY conversion from r12 to 134

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  #1  
Old 06-25-13, 11:01 AM
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DIY conversion from r12 to 134

I just got a pretty nice condition 1982 Mercedes Benz and most of the 'systems' are in good shape or I made some (straight forward)repairs to the must fix items: steering damper, exhaust, O2 sensor, etc.

The A/C is inop ( now to the nice to fix items ) and thats next on the list.

I am hoping for some inputs to help with my decision:

I pressed in both schrader ( sp??) valves and neither seems to have any pressure behind them (neither high nor lo pressure side) Does that mean that the system is essentially depleted of gas? ( its an r 12 system)

If that's the case there is obviously a leak or leaks. Although the car has essentially sat with almost no use for 12-15 years

Since it seems a lot easier to maintain, a conversion to 134 would be reasonable to me and doable.

So, how do I start? I have done on line research and compared to having it done in a shop, I think I can do it at about 2/3 the cost even considering purchasing the equipment.

If there is some experience please check my list of needs:

I will likely (easy enough to change out) buy a new compressor. Its an A6 ( I guess a fairly standard and reliable Harrison of that day and age) and there is an aluminum version for about $275, new. Sounds pretty good. Buy a new evaporator. Not too much $$$

I will need a vac pump and lines with gauges ( what size is adequate for a DIY'er in the driveway?) For under $200 seems you can get a reasonable set up on amazon.

What fittings are needed? How 'standard' are Mercedes (of this vintage)? I know you need the conversion to 134 fitting for the car and what else?

Need some type of flush set up and flush fluid. Some people say a gallon of alcohol is fine, do you need commercial flush fluid? Again, amazon lists flush kits. Comment is to get one that you can run off shop air without charging, recharging etc. I have a 60 gal compressor so thats not an issue

Since it appears there is no pressure in the lines, there ought not to be an issue of release of r12. So no need to capture the r12.

What about the O rings? I can buy a set of replacement rings for 10-15 dollars that supposedly fit this car. Seems reasonable to replace anything that uses O rings

How about dye solution? I can get a small UV light for $15-20. Do those work OK for a one time use? How do you inject the dye into the system?

What about the hoses? They appear to be in good shape. Is a visual-feel inspection adequate? They seem expensive so if not needed, I do not want to replace them.

Then there is an orifice tube somewhere? Where is that located? Seems inexpensive and a 'must change'

I have read lots of how to's-cautions etc and it seems fairly doable and I would feel a lot better about completing this myself. At least I'd know what was or was not done.

There is still the question of the electrical controls but the mechanical part has to work anyway.

Any ideas and answers to my questions are appreciated.
 
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  #2  
Old 06-25-13, 11:20 AM
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I did my 86 reliant k car a while back...

I will likely (easy enough to change out) buy a new compressor.
No. Just need to get all the old oil out.... Thats what I did.

What about the O rings?
Yes new rings...

What about the hoses? They appear to be in good shape. Is a visual-feel inspection adequate? They seem expensive so if not needed, I do not want to replace them.
Must change to r 134 hoses. The r 12 hoses will let the r 134 pass through. Different molecule size...

Then there is an orifice tube somewhere?
Must change orfice yes..

Mine had no orfice but a square restrictor block I had to change.


Personally I would keep it r 12 if you can... The issue you will have is the condenser is most likely not big enough for r 134. On hot days I had issues and had to put the fan one spot below hi to keep cool.

You will know its undersized when you spray water on the condenser and the duct temps drop a lot....
 
  #3  
Old 06-26-13, 07:36 AM
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A/C hoses

If the original (r12) hoses appear OK, how long does it take for the 134 to permeate through them? Is it like a day, month later or needing a recharge 2 or 3 years later?

And I guess suggestions are to replace the accumulator?

Thanks
 
  #4  
Old 06-26-13, 08:07 AM
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When I did my retro fit I assume the thoughts were different back then. Frome reading some I guess they changed that assumption..

Also the old oil removal was important. I remember draining my compressor of old oil / flushing/ and adding new....

( Text from link below)

When R-134a was first introduced, it was thought that all non-barrier/nitrile hoses would have to be replaced during an a/c retrofit. Early laboratory tests showed that the small R-134a molecules leaked through the walls of non-barrier hoses more readily than the larger R-12 molecules did. In the lab, this caused unacceptably high leakage rates. More recent testing, however, has shown that oil used in automotive a/c systems is absorbed into the hose to create a natural barrier to R-134a permeation. In most cases, the R-12 system hoses will perform well, provided they are in good condition. Cracked or damaged hoses should always be replaced with barrier hoses.

Unless a fitting has been disturbed during the retrofit process, replacement should not be necessary. Most retrofit instructions call for lubricating replaced O-rings with mineral oil to provide this protection.


read all here. I hope this helps...

Guidance on Retrofitting to HFC-134a | Ozone Layer Protection - Regulatory Programs | US EPA
 
  #5  
Old 06-26-13, 09:04 AM
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Oh here was my conversion...

Note the block behind the pressure switch... Has that little tap thing ontop. I changed that.

Hoses came with new dryer??? The canister thing.

But I cant remember if I changed that black canister that has the glass eye.. I think I just drained that of oil and added new... I believe that just is an oil retention can??? Now looking at it it looks shiny and new.

Important to flush and clean the coil....

Just had to change port on compressor also, but you see original..

All in all it cooled fairly well......

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  #6  
Old 06-27-13, 05:44 AM
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Another question: how about the fittings? Replacements screw/snap onto the old r12's?
 
  #7  
Old 06-27-13, 06:50 AM
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What fittings are we talking about?
 
  #8  
Old 06-29-13, 03:00 PM
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The dryer is just what the name implys. It contains a dessicant to remove any moisture that might be in the system. Its a good idea to replace them any time the system is opened up.
 
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