bazx -- You mentioned earlier that you were having problems getting the final stage to work with R14, but apparently have had some success with the R1150. Ever think about doing a mixture of both the R14 and R1150, and perhaps installing a subcooler? It works great on autocascades with R14 and Argon, and I don't see why it wouldn't work with what you are doing. In fact if you want to avoid the cost of R14, try ethylene and methane (with a subcooler). Should be similar to the R14/Argon mix, but just not as cold.