Since the poster is in Canada, he does not have access to R-12. Our northern neighbors completely banned R-12; he has no choice but to convert.

That said, I'll second Larry's opinion. You are very unlikely to get good results with a so-called "death kit." R-134a will be sufficient for a Canadian summer, but you need to do the conversion correctly - flush the system, fix the leaks, recharge correctly.

And no, you cannot just release the remaining R-12 from the system. 1) It is illegal to do so. 2) The system must be evacuated before charging - any air inside the system is a very bad thing.

- JimY