Air Condition o-ring retrofit for R134. Does it work

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All,

I have heard that the R12 A/C system in our 71/73 mustangs can be retrofitted to work with R134. I was told the o-rings need to be replaced with "green" ones and purge the system then fill with R134. Is this true? What else would need to be done? I cannot afford an after market replacement and the one in my 72 mustang is in great shape.

Thanks

Brian
 
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This is a decent article on the subject. https://newoldcars.com/r134-conversion-think-twice-before-you-do-it/
My personal experience with 2 originally R-12 vehicles is very HO-HUM and a bit of a PITA. Results were poor, output in the middle 50 degree range even with a larger capacity condenser and new filter drier. I never attempted it after that. Others may have different and better results. Chuck
 
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You can definitely do it. I have done it in a 72 olds, but it has never been as cold as with R12. It works, and it will keep you cool, it just may take a while longer to get there and again not as cold as R12. You do need to vacuum the system to get everything out of it, you need a different oil, and if you are doing this you should put some dye in it to find leaks, and yes you will need to change the o-rings. Tons of videos on YouTube on how to do it.
 

Retired2014

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‘Purge the system’ means flushing each component; condenser, evaporator core, individual hoses and the compressor of the old oil and residue prior to refilling with the new oil and 134. The compressor cannot be flushed without removing it and either pulling off the back plate and cleaning out the old oil or possibly flushing through both fill port bolts, top and bottom. When I did my flush, I found considerable oil in the evaporator core. Apparently, if you have a slow Freon leak over time, the oil will drop out inside the evap core and remain stagnant. The TXV ( thermal expansion valve) located at the firewall where the evap core lines exit cannot be flushed but must be removed to access the evap core lines for flushing. The filter dryer next to the condenser must also not be flushed, but replaced. The desiccant inside is apparently degraded by the flushing solvent. Flushing is made easier by using O’Reilly’s tool loaner program and ‘borrowing’ their flush tool. A/C Flushing solvent is not cheap, but is safer than alternatives like lacquer thinner due to the highly flammable nature of that stuff. That said, I used lacquer thinner followed by a ‘rinse’ with the expensive stuff. If you do the flushing outside the flammability issue is lessened. I attached a 5’ section of clear vinyl tubing to the ‘exhaust’ end to keep the lacquer thinner away from the under hood paint. I purged with LOTS of shop air to thoroughly remove all traces of solvent, as it will degrade the new oil. The old R12 system uses mineral oil and the 134 system uses a PAG oil. I took about 4 hours to flush the lines and components on my system, the TXV removal is a PITA…
 
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A friend who is also an AC tech recommended I look into this stuff for R12 replacement. Probably similar to the FR-12, mentioned above.

 
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All,

I have heard that the R12 A/C system in our 71/73 mustangs can be retrofitted to work with R134. I was told the o-rings need to be replaced with "green" ones and purge the system then fill with R134. Is this true? What else would need to be done? I cannot afford an after market replacement and the one in my 72 mustang is in great shape.

Thanks

Brian
You need to replace the original R-12 compatible refrigerant oil with a refrigerant oil that is compatible with R-134 as well.
 

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There are several R-12 substitutes on the market, I believe most all are refined propane/isobutane products. They work with and are compatible with R-12 and the existing mineral refrigerant oil in a R-12 system. There are some folks that are hesitant to use a flammable gas in their car a/c system citing fire hazards with leaking propane and ignition sources like stray sparks. I think that pales in comparison to the 15+ gallons of gas we have available on board to feed a fire, but that’s a personal opinion, open to argument. Flammable refrigerant gasses are prohibited in public conveyance systems like busses due to some tragic fires, but now Pentane, a refined hydrocarbon gas is the refrigerant of choice in your new home deep freezer, so there’s that hiding in your home too…
The limited amount of flammable refrigerant in a vehicle system even with a slow leak is ‘probably’ not a huge concern for me, but it comes down to personal choice and always $. Weigh the pros and cons I guess. Certainly the “no smoking” lamp should be on when adding R-12a to your vehicle.
 
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R 290 has been in widespread use in Europe for decades. Chuck
 
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