I was under the impression to do a complete R-134 conversion you need to evaluate the R-12 and clean the system, replace the receiver-dryer, then recharge the system with R-134.

If you are going to be rigorous, you also need to replace the A/C hoses with the new R-134 barrier hoses. (R-134 has smaller molecules and will leak out of the R-12 hoses more easilly over time.)

The lubricants that are used in R-12 and R-134 are incompatible. If you system is not clear of R-12 lubricant, and you charge with R-134, you risk compressor damage.

Here is a good link from the EPA that discusses R-134a retrofits.

http://www.epa.gov/spdpublc/title6/609/technicians/retrguid.html

Also, here is a link to a table that shows all the R-12 alternatives, and what their characteristics are and composition.

http://www.epa.gov/spdpublc/snap/refrigerants/macssubs.html

Todd
'88 Westy

 -------------- Original message ----------------------
From: Roger Sisler <rogersisler2000@YAHOO.COM>
> It may be that they told you something you have not written here. It is
> pretty difficult to snow somebody for two hundred dollars for just a
> recharging. These are very common.So are the snow jobs,though.
>
> If it is a pure 134a retrofit,you can buy a can of 134a and a hose/gauge at
> Advance auto for about $25.You can reuse the hose ,next time and the
> recharge will only cost $11,then.
>
> Recharging is ez to do. The 134a hoses are quick release,so they wont scare
> you to death attaching and removing them. 134a works at pressures  20%
> higher than R12,so it will leakout that much faster.The hose will only
> attach to the low side for charging.You cant make the mistake of attaching
> to the high pressure side.
>
> The Advance auto hose dosent use numbers on the gauge. Only three
> colors,instead.Charge the system up till the needle is in the green
> area,and you have done all you can do as far as a recharging goes.
>
> Make sure you dont have a freeze 12 system,first.If your retro fit shop did
> it right,they will put a sticker in the engine compartment that tells the
> refrigerant used.
>
> Good luck,Roger