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To do this job right you will need to clean and remove all the mineral based oil from the system including the evaporator, condenser compresser and accumulator. The best way I found to do this is to take the entire system apart and use a non-chloronated brake parts cleaner or acetone if you are a non-smoker. Mineral based oils give up their hydrogen to the R134 leaving carbon behind that mixes with the broken down oil and galls up the compresser, clogs the orifice tube and deteriorates the interior of the hoses. PAG or ester based oils have a modified carbon chain that does not break up hence its compatability with R134A and R564, both are common household "computer" dusters.
Do this job right and clean out the old oil using a flush method. Once this is done pull a vacuum and sweep charge the system after you have added some ester or PAG oil to the compresser. This will get the internals oiled without sweeping the oil into the system, you will have to short the cycling switch to pull in the clutch. After five or so minutes begin the charging using only R134A gas to the low side port, do not allow liquid into the system at this point as it will foam up the oil. Once the low side shows around 10 PSI you can charge at a fast rate if you wish to bring the system to 15 PSI and remove the shorting wire from the compresser. The best way to charge is to use the superheat calculation method taking into consideration ambient temp, humidity condenser discharge temp and low side suction temp. A good but not so accurate tell-tale is condinsate on the accumulator and metal portions of the suction side lines. Dont expect the system to cool as well as R12 unless you drill out the orifice by one wire drill size to compinsate for the refrigerant and lowered cycling cutoff pressure, this is adjusted by a screw that is located between the terminals on the CCOT switch. You will have to experiment with its setting to get it right.
Sounds like a lot of work and it is however if you take the additional time you can literally create an icebox on wheels that is also very efficient. How does an air discharge temp of 36 degrees sound? Did this to my sons 245DL and it will put frost on the windows.
Badge 988
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