Report Fan Control in Vision & Samba PLC + HMI Controllers & VisiLogic Software Posted September 1, 2013 Instead timer, maybe you can try ot set a little hysteresis. Please check the example ON-off control in VisiLogic. I'll divide the conditions to start and stop the fan for both temperature and humidity setpoints and they both will operate bits. Then will OR these bits to activate the real output. This seems to me easy for edit and debug.