Problems using mvsCodePage user property

Hello,
I use RTC/z server version 3.0.1.
I need to build C code in the USS partition. The C code is stored in ASCII.
When the code is fetched to the Build Engine (USS partition) it must be converted to EBCDIC.
In a post I found that you can set the user property mvsCodePage to have the fetched file converted to a different code page.
I tried mvsCodePage=IBM-037, but it had no effect.

Am I doing something wrong?

Thanks for your help,
Ilaria