On aircondition.com discussion forum, these are referred to as "death kits." This doesn't mean the death of the owner, but rather the death of the air conditioning system that they are used on.

R12 is coming back down in price, so it is becoming more and more feasible to stay with it. If you want to switch to r134 I strongly suggest that you do it right by completely dismantling the system, flushing everything everywhere, put it back together with the correct o-rings, replace the filter drier, use r134 compatible oil and evacuate the system thoroughly before charging the system with GUAGES.

My $0.02,