R-12 to R134-A question

rgp266 · Mar 12, 2015

When doing the conversion from R-12 to 134-A is there a conversion formula for how much 134-A to recharge the system with or just go by high side pressure and duct outlet temperature?

What effect does altitude play in pulling vacuum on the system? Can you get to 28"-30" HG?

Thanks........
Bob

The Horvaths · Mar 12, 2015

Ripped from classicautoair's web site:

1962 & Newer Systems

Minimum Requirements:

Change or restore the filter-drier.
Drain the compressor oil and recharge with 134a compatible oil. (PAG or Ester Oil)
Insure that the system is clean and free of contaminants (Depending on component condition, this may be a simple matter of blowing out with compressed air or liquid flushing with an air-conditioning flushing agent)
Replace or restore all rubber hoses with barrier hose.
Remove EPR valve from compressor’s suction port
Install thermostat.
Charge with 134a between 70-80% of the original R12 charge amount.
Replace any o-rings with 134a compatible.

HELPFUL HINTS

Ignore the sight-glass. A properly charged 134a system will likely show bubbles in the sight-glass.
Typical 134a charge rate will be approximately 70-80% of the factory R12 charge amount.

Note: some of those items listed are not exactly in order of precedence.
As for vacuum -vs- altitude, if the system is sealed, altitude will have virtually no impact on performance of a properly functioning vacuum pump.

red72 · Mar 12, 2015

Altitude will not have any effect on the vacuum you will be able to achieve in the system. A good rule of thumb is to weigh in 80% of the original factory charge specified for your system. For example, if the system originally had a 3lb. charge (48oz.) weigh in 38.4 oz. of the 134a and check the system operation. You should be close.

Speedbird · Mar 12, 2015

Not asked, but I think the filter dryer MUST be changed if yours is for R12.
I think the material is not compatible and will come apart in the system.
Also, I've "read" that if your hoses are old and hard, they might be OK to use.
The smaller 134 molecules won't be able to leak out, which is the concern if you don't change hoses.

rgp266 · Mar 14, 2015

Thanks to all. I am aware that most of the components need to be changed or rebuilt to be 134-A compatible especially the Receiver/Drier or Accumulator depending on who's system you are working on. The big question was the vacuum issue and charge percentage.

Bob

rscurtis · Mar 14, 2015

Stay with the R12- it's a much better refrigerant that 134. It cools better, does not have the propensity to leak, runs at lower pressure, and is not as corrosive if any moisture gets into the system.

themechanic · Mar 14, 2015

Put in some dye to make it easier to find leaks.

A383Wing · Mar 14, 2015

o-rings do not need to be changed, but the receiver-dryer would be a good idea to change

R-12 to R134-A question

rgp266

Well-Known Member

The Horvaths

Well-Known Member

red72

Well-Known Member

Speedbird

Bird of Pray

rgp266

Well-Known Member

rscurtis

Well-Known Member

themechanic

Oklahoma is OK

A383Wing

Well-Known Member

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