Does anyone do a search before posting? Sorry, not trying to flame anyone, but there are a million threads on Stangnet about this. But, here goes again.
Basically, the retrofit kits you see in Wal-Mart, K-Mart, Autozone, ect. are a fix-it-fast kind of deal, usually temporary fixes with big consequences.
Some people have success, some don't, it depends on the condition of the system in the beginning. You must diagnose an A/C system as a whole, not just an individual compnent. So the compressor failed? why did it fail? Probably because it was starved for oil, caused by a low system charge or partially blocked orfice tube.
here are some notes about retrofitting.
You must replace the filter-drier/accumulator. The dessicant, or drying agent, contained in it isn't compatible with 134a, it will break down and circulate through the system, eventually plugging up the orifice tube. This is usually why an improper retrofit usually results in compressor failure.
You must remove all the old oil R-12 oil from the system.
The system needs to be flushed, but DO NOT flush rubber hoses. The mineral oil coates the inside of the hoses forming a barrier. Flushing the hoses will remove this barrier. Since the R134a molecule is smaller than the R12 molecule, you usually will make several small leaks. If the compressor is trashed, obviously you will have to flush the whole system and/or hoses.
There are aftermarket orifice tubes for 134a conversions to make the most of the system, they are quite expensive but well worth the money. I have done 3 retrofits so far this year with nothing but success using that orifice. All three vehicles blew 30 deg. out the vents after the retrofits. This was on an average of a 85 degree day with about 40 percent humidity. I think that's plenty cold, now granted this is using the replacement orifice that's auto adjusting.
When you take the system apart to flush it, turn the compressor over and get all the r12 oil out of it you possibly can. Then, go buy a bottle of Energy Release. Use 2 oz of energy release in the compress plus the normal 3 oz of PAG oil. The reason for the Energy Release is to protect the compressor from the new higher pressures of the 134a refrigerant. The refrigerant in the system won't move the ER, it will stay in the compressor and keep it lubricated no matter what, in addition to keeping the operating temperature of the compressor at a minimal.
Make sure to vacuum the system for AT LEAST 45min to 1 hour, then a 15 minute wait to see if you have any leaks.
Next, make sure to charge the system with 90 percent of the specified charge, 134a is heavier than R12 and therefore less of a charge is required when retrofitting.
I have heard of and seen Freeze 12 used, and a lot of people have great success with it, but it is a blended refrigerant and could in time, break down into it's base components and ruin the system, but i have never seen or heard of this happening to this day.
Remember, it is illegal to "top off" an existing system or attempt to service it without proper training, so says the EPA. Although you don't have to have a licence to buy R134a, go figure.
Any questions?