r409a or 134a?

[AndrOvr]

what would u pick? r409a or r134a...
I have one 1/4hp r12 compressor.

I want the best one for low temps.
I dont have any other freon available :(


Im doing the same as this guy... (small evap. for cpu cooling)
http://www.refrigeration-engineer.com/chat/showthread.php?s=&threadid=843

[bhrobin]

AndrOvr --
The first consideration is the type of oil used. If your system already has mineral oil or alkybenzene oil in it, you may want to stay with R-409a. It is quite suitable for lower temperatures. We have used it reliably in ice cream machines and walkin freezers. The R-409a will also work fine in systems with Polyol Esther oils.
I am not aware of any large number of people using R-134a for very low or low temperature applications. For that reason alone, I would stay away from it at those temperatures. If you are just looking at evaporator temperatures of -10ºC or so, the R-134a should be fine. Much below that would concern me because I am unfamiliar with use in that range.:)