<VV> a/c recharge question

[NicolCS@aol.com]

<snip>
Hey gang, 

The hot weather is coming and I need to recharge my AC.  I will attempt to 
reseal the seals, etc. to avoid tearing down the system.  However, my 
question 
has to do with the replacement coolant that has been recently introduced.  
Enviro-Safe, Freeze 12 and MacFreeze (No, that isn't a McDonalds dessert.) 
all 
claim to be replacments for the original R12 freon.
<unsnip>

Well, here goes...
There are two types of refrigerant, "pure" types and "blends" all those you 
mention are all blends. Freeze 12 for example is 134,142 and another one I 
can't remember.  The blend has to have a precise ratio between the components to 
work properly, and they all do work properly when first installed.  I have used 
Freeze 12 on occasion and have been happy with the "cheap fix" aspect and 
initial performance.  Here's the catch with blends: One of the blend elements 
will bleed off faster than the next so as your system leaks down, the blend 
fractions will change.  Eventually you will have two gasses instead of three and 
then just one.  The cooling performance will fall off when the blend percentages 
go "off."  You can't just top it off to restore proper function because the 
"top-off" will contain all three gasses.  To get it back to efficient operation 
in a "blend" refrigerant, you have to sweep the system and start over. 
Then there is R134a and R12.  These are both "pure" single compound 
refrigerants so as the system bleeds down, all you have to do is add more.  A/C 
component warranties are only valid if the system has 12 or 134 in it.  Sure, 134 
doesn't carry quite as much heat as 12 but that merely delays "max cold" cabin 
temperature.  I have converted all my vehicles to 134 and I'm very happy.  I 
sell my 12 to customers for top-off but if the system is empty or I am doing a 
major repair, I always convert to 134.
Well, there's one opinion.  May the fur fly!
Craig Nicol