Thread: R12 to R134
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kuehl kuehl is offline
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Join Date: Aug 2004
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You have several options to get your ac system up and running. However how effective of a system you want will depend upon your climate needs; do you use the system often, are you in a hot climate, etc.

With R12 the refrigerant oil was what they call a mineral oil whereas R134a uses either "ester" or "PAG".

R134a requires a different desiccant (what is in your receiver drier) and requires different service charge ports (ref: your schrader valves).

Why you would want to "lubricate your system" .... I don't know. Normally the system is a closed loop system; it does not consume oil alike an engine. The only time you need to add oil is when you have had a refrigerant leak or you have replaced a component. The oil circulates through the system with the refrigerant and constantly lubricates the compressor; the compressor does not have a sump. But I don't want to discourage you from thinking about your systems ac oil... its a good idea since many of our 911's or or 930's have been passed down to many owners and the ac system repair history is vague; in many instances someone may have "topped off" due to leaks however they failed to add oil.

R134a condenser side pressures tend to run on the average (industry jargon) 10% higher than R12. Hence you either use less refrigerant or use a higher capacity or efficiency condenser system.

There is an option for you if you simply needed to add a lubricant other than mineral oil, you could use "ester" refrigerant oil. Esters tend to mix with mineral easier than PAG and it is very common to simply add ester when converting to R134a refrigerant. In a perfect world (you got the time and money) you would flush the system to remove contaminants that collect over the years (drier desiccant break down, compressor break down and hose break down) in the hoses, condenser and evaporator (you don't flush compressors or driers) prior to converting to an alternative refrigerant. However, its a proven fact that flushing is not necessary for a simple R134a conversion.

A "simple" R13ra conversion requires removal of the compressor, dumping of whatever oil remains in it (usually little), replacement of the receiver drier with a new drier that has R134a compatible desiccant (XH7 or XH9 desiccant), replace any o-ring on any port you have opened or component connection you have opened with o-rings made from HNBR (Hydrogenated Nitrile Butadiene Rubber), evacuate system for 3 hours, charge with a nominal amount of 85% by weight of the original R12 charge using R134a (example: if the system originally used 39 weighted ounces of R12 you would use 33 ounces of R134a) and fine tune (add or remove refrigerant) the charge based on an R134a Pressures and Temperatures chart.

Adding R134a to a system that has R12 can be done however its not recommended; when R12 and R134a are mixed together they form a high pressure azeotrope. This means that together their pressure is higher than either by themselves.

Getting back to the basics, a 930 has over 40 feet of refrigerant hose. The original hose is what we call "non barrier"; designed over 50 years ago; leaks or permeates refrigerant over time. So no matter what you will be constantly topping off or recharging your system since the stock hoses simply leak (the leakage rate or permeation rate is based on pressure, temperature and time). The solution is replacement with new barrier hoses.

Feel free to PM if you need more guidance.
Old 08-29-2007, 03:58 AM
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