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RETROFITTING TO R134a

When the idea of retrofitting vehicles with R12 systems to R134a. was first suggested much misinformation was dispensed by well meaning individuals who had text book knowledge but no practical experience mainly because it hadn't been done yet.

IT'S NOT VERY DIFFICULT OR COMPLICATED!!!! 

The necessary steps you need to follow are identical to those you would take to properly perform any AC repair.

If it ain't broke, don't fix it!      

It is often suggested that it is necessary to change orings to R134a compatible materials and to upgrade hoses to the newer barrier hose.  This is not true.  The older hose under pressure will eventually become impregnated with the oil from the system and form its own barrier.  If your hoses aren't leaking there is no need to change them.  Of course, if you do need to change them it only makes sense to use barrier hose.  

The same holds true for the orings.  The main difference between buna orings and the recommended HNBR orings is the maximum operating temperature, or heat range.  HNBR is more durable and will withstand more heat for a longer time but in all probability, some other component will fail long before the buna oring deteriorates.  By all means use the compatible orings when changing them as part of servicing another system component, but do not create unnecessary work to change an oring which is otherwise OK.

WHAT YOU NEED TO DO THE RETROFIT.... 

Forget about buying fancy kits.  It is just a ploy to separate you from your money.  You will need to purchase high and low side adapters and synthetic R134a compatible oil.  You will also need to thoroughly flush the system and remove as much of the mineral oil as possible (within reason - no need to be anal retentive about it) and change the drier or accumulator.  Since this is part of properly servicing the system anyway, the only real difference between a retrofit and any proper service is the introduction of synthetic oil and the use of adapters.  

CHARGING YOUR RETROFIT SYSTEM

Once you have completed servicing the system, installed the adapters and used the appropriate oil you are ready to charge  the system.  Remember....

MORE IS NOT BETTER 

A retrofit from R12 to  R134a requires less gas.  LOOK UP THE PROPER R12 CHARGE!  DO NOT GUESS!  Calculate 70% of the correct R12 charge and start by putting in that amount.  Give the system some time to stabilize and if you have cold air stop.  If not keep adding in small increments until the air gets cold.  Monitor pressures with your gauges keeping in mind the normal readings for your system which you also LOOKED UP.  How cold an AC system gets is determined by the low side pressure.  The lower the low side pressure, the colder the system.  Adding gas beyond optimal pressure will decrease the systems efficiency and eventually raise the low side pressure.    Lowering it too much (beyond the manufacturers specifications) will cause freeze ups and the activation of system electrical switches designed to shut the system before freeze up occurs.  That is why you do not want to significantly deviate from the manufacturers suggested charging parameters.  When you are done affix a label to the evaporator case or somewhere under the hood indicating the amount and type of gas used for the charge, the amount and type of oil, the date, the pressures read on the gauges and the ambient (outside) temperature.  All of this information will be useful in the event you have to service the system at some time in the future.

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