Works like a charm!
For anyone that want to use this, put this in your macro:
*while sensors.analog[2].lastReading < 50
G4 S1
M99*
And your startup script:
*M98 P"0:/macros/Chamber temp/chamber_temp_50.g"*
And of course name it to what you want and set the correct sensor number and temperature. And be sure to use RRF 3.01-RC4 or later.
Thank you for your help.
/Christian