ON-OFF function and txt loaded file

Thanks for the tip: very useful!But the problem lasts when T<30°C: if I put 0 in the expression, this zero is a value for COMSOL, and actually I would like to stop the injection, not to inject air at 0°C... how can I express this?
Sorry if I sent a private message but i didn't menage to post in the topic!
Kind Regards,

Stefano.