# R12/R134A Conversion



## Davans (Apr 12, 2008)

I'm changing on over from R12. Does anyone one have a weight conversion chart? The car takes 3.75 lbs of R12.


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## GoldDot40 (Apr 13, 2008)

What type of vehicle is it? The reason I ask is because in some vehicles, it's not as easy as just screwing on retro-fit fittings and filling it up with R134. Some 1993 and older R12 systems aren't as 'compatible' as you'd think to switch over. Some vehicles' older hoses will allow the R134 refrigerant to 'seep' through the linings on the hoses. R12 and R134 are of different chemistry. Some vehicles won't be a concern. I'm just trying to help you avoid headaches in the long run.

Another thing also. Do you have an evacuation pump to vacuum down the A/C system before you recharge it? This is extremely critical to allow the system to accept the proper total amount of refrigerant and oil. It would also be a very wise idea to 'flush' or have the system flushed before you charge it. What about your orifice tube and expansion valve? They in good shape? All these steps will help you get optimum efficiency from your A/C and are very doable at home. Do you have a Chilton or Haynes book for your vehicle?


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## Davans (Apr 13, 2008)

It is an 81 vette. 
We are replacing the comp. , orifice, accumulator, hoses and all o-rings. flushing the rest of the system and yes we will be evac & charging. The only thing i'm stuck on is the amount of R134a.
Thanks for your input.


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## badger (Apr 13, 2008)

Typical R-134A charge is 90% of the listed R-12 charge.


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## GoldDot40 (Apr 13, 2008)

Davans said:


> It is an 81 vette.
> We are replacing the comp. , orifice, accumulator, hoses and all o-rings. flushing the rest of the system and yes we will be evac & charging. The only thing i'm stuck on is the amount of R134a.
> Thanks for your input.



Good deal. Now you'll be cool in more ways than one. Nothing like doing it right the 1st time.

BTW...3.75lbs = 45oz


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## HGM (Apr 13, 2008)

I've always used 80% of the R-12 spec. Some of the kits actually tell you that too..


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## Davans (Apr 13, 2008)

Thanks guys. Now i got a math question.
3.75lbs = 60 oz.
60 oz @ 90% would be 54 oz.
60 oz @ 80% would be 48 oz.


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## HGM (Apr 13, 2008)

Looks right to me..


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## badger (Apr 13, 2008)

HGM said:


> I've always used 80% of the R-12 spec. Some of the kits actually tell you that too..



BTDT........
Have had evaporators ice up more than once using 80% in BMW's & Porsches. Some experimentation led me to the 90% charge & it works well for me.


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## HGM (Apr 13, 2008)

Could be... Most of what I have worked on has an orifice tube or evap temp sensor to keep from icing.. I've noticed older TXV's tend to be more sensitive to icing.. The only issue I would have in the back of my mind is that on an '81 vehicle with the higher pressures of R-134, you may be asking for evaperator issues.. Either way, I wouldnt go 100%, 80-90% should work just fine.. Plus, its easier to add refrigerant than take it out. (leagaly)


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## kudzumotorsports (Apr 13, 2008)

I dont want to be different here but I have had the best luck at 75% charge. Unless the vehicle has an electric fan with a high side pressure switch that will activate the fan when a predetermined pressure is reached.


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