CONCLUSIVE!
Thread Starter
Drifting
Joined: Sep 2001
Posts: 2,467
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From: redmond wa
CONCLUSIVE!
"Legacy" non-barrier A/C hoses DO NOT leak absent system pressure beyond their design specifications.
Both the EPA and SAE are now on record stating that converting a Porsche 911 R-12 system to R-134a DOES NOT require switching to non-barrier A/C hoses. Once the original factory "non-barrier" hoses in our 911's have been "saturated" with the lubricating oils used with the R-12 refrigerant they will not leak R134a refrigerant.
That also means, obviously, that the factory use of non-barrier hoses is NOT the source of long term, ~2 years, refrigerant loss in our cars, R-12 or R-134a, That many of us have experienced, are experiencing.
Then what is...??
System high side pressures that exceed the design specification for those OEM, factory installed, non-barrier hoses.
Even Kuehl, along with both of the above entities, recommends the use of a binary pressure switch to prevent compressor "over-run", when converting to R-134a. The basis for this recommendation arises from the use of a "vent-to-atmosphere", pressure relief valve, used to alleviate inadvertent system over-pressuring, on many older systems.
Since R-134a typically operates at higher system pressure vs R-12 these BOVs are likely to vent some of your refrigerant absent a method of prevent those pressure spikes absent some preventative measure(s).
But will preventing the compressor from over-running and thus over-pressuring the system be a complete solution for our Porsche's.
Maybe not.
We may need a method for keeping/"starting" the front lip condensor fan whenever system high side pressure exceed a specific level....a TRINARY pressure switch with the extra element used to power the front lip blower regardless of ignition switch position.
The mere existance, and current availability, of 450 PSI refrigerant pressure relief valves/fuses used with many "legacy" R-12 automotive A/C systems would indicate that even R-12 system overpressures in that range are possible. So to what surge/spike pressure level might we see when converting to R-134a if no preventative measures are taken?
Both the EPA and SAE are now on record stating that converting a Porsche 911 R-12 system to R-134a DOES NOT require switching to non-barrier A/C hoses. Once the original factory "non-barrier" hoses in our 911's have been "saturated" with the lubricating oils used with the R-12 refrigerant they will not leak R134a refrigerant.
That also means, obviously, that the factory use of non-barrier hoses is NOT the source of long term, ~2 years, refrigerant loss in our cars, R-12 or R-134a, That many of us have experienced, are experiencing.
Then what is...??
System high side pressures that exceed the design specification for those OEM, factory installed, non-barrier hoses.
Even Kuehl, along with both of the above entities, recommends the use of a binary pressure switch to prevent compressor "over-run", when converting to R-134a. The basis for this recommendation arises from the use of a "vent-to-atmosphere", pressure relief valve, used to alleviate inadvertent system over-pressuring, on many older systems.
Since R-134a typically operates at higher system pressure vs R-12 these BOVs are likely to vent some of your refrigerant absent a method of prevent those pressure spikes absent some preventative measure(s).
But will preventing the compressor from over-running and thus over-pressuring the system be a complete solution for our Porsche's.
Maybe not.
We may need a method for keeping/"starting" the front lip condensor fan whenever system high side pressure exceed a specific level....a TRINARY pressure switch with the extra element used to power the front lip blower regardless of ignition switch position.
The mere existance, and current availability, of 450 PSI refrigerant pressure relief valves/fuses used with many "legacy" R-12 automotive A/C systems would indicate that even R-12 system overpressures in that range are possible. So to what surge/spike pressure level might we see when converting to R-134a if no preventative measures are taken?
Last edited by wwest; May 16, 2013 at 02:27 PM.
