The way I understand it is there are 3 different types of conversions. and I may have them mixed up. I think this is how it goes. Type 1-the first- A complete kit, with evaporator, condensor, compressor, rcvr/drier or accumulator (whichever applies), orifice tube, and a new compressor. Type II-the next introduced. New accumulator or rcvr/drier, orifice tube and o-rings. Type III- The most recent and probably the most commonly used. R134A in a can along with a sticker and R134 connectiion adaptors which must remain on the vehicle for legal purposes (EPA requires labeling the vehicle in a noticeable area, because refrigerant can be recycled in the recovery machine and then resold to the customer or reused later on.) The reason it has been labeled the "Death kit" is because a lot of people just buy the adaptors with absolutely no knowledge of refrigerants throw it in the lines and cause damage. I tend to live by the medaphore "better to measure twice and cut once, than to measure once and cut twice" However, I feel if done properly any type of conversion will work. Swapping to all new parts is just a sales pitch. What one must understand is refrigerant boils at somewhere around -22 degrees fahrenheight. Moisture in the system both changes the boiling point and can cause severe damage to the compressor. I'm sure the companies that rebuild air compressors love the diy's who don't take the proper steps. Personally, if all original parts where still intact or available I would go that route. Just take a few precautionary measures and it will be pain free and save you a whole bunch of money. Here's what I would do.
1. Replace all seals, while the system is open go ahead and replace orifice tube (if equipped)
2. Drain all oil, etc.
3.A MUST TO PREVENT the "DEATH KIT" --find your local shade-tree mechanic or someone you know who will cut you a good deal. Dealerships, etc will want to sell the R134a with the "ac test". Have the system vacuumed down and leak tested. If the system will hold a vacuum you just killed two birds with one stone. You have found out that your system is not leaking (saving you money from numerous recharges), and probably the most important and biggest mistake that people make is that this vacuum removes the moisture from the system which is essential to both-proper operation of parts and good cooling.
4.ONLY AFTER the system is under a vacuum and holds that vacuum go ahead and add 80-85% of recommended free-on. you may want to note this doesn't count oil. If recommened is 40 oz. you need about 32 ounces of r134a. Most of the cans of R134a is mixed with oil for ease of installation. A 12 oz can of R134a oil and refrigerant is about 8 ounces of refrigerant and 4 ounces of oil. This would require not 2 1/2 cans but more along the lines of 4 cans to make 32 ounces of refrigerant. (double check this number and the amount of oil to add when buying the refrigerant, I'd hate to tell someone to overcharge their system)
5.Put label in clear to read area and enjoy your air and take the $400 you just saved and have a