G-BBYB

Thanks Allan, I will give that a go, I am not sure I can set the mix to exceed 100% from memory it was -100 to +100??

You have confirmed that I am not doing something silly, which is great thank you for that. The manual shows how to do it, and it uses the three pos switch, it does work, but with reduced throw as if the centre was wrong as you say.

I may be able to alter the servo throw so that it activates the air valve even with the reduced throw, might be simpler..... How do others get around this then?

Cheers
Danny