I have setup a truth table to control an exhaust fan based on the humidity feedback from a thstat. below is the following tt

Fan on         H L L L
Fan off         X H L L
Fan auto       X X H H
Hum FB Not  X X H L
Hum FB        X X L H
                    H L H L Exhaust Fan On
                    L H L H Exhaust Fan Off

What is happening in the Auto state ( On, Off, Auto are set by the user) the fan will never turn off when the Hum FB not goes low and when the hum fb goes high.

If anyone can provide some feedback as to why the fan won't shut off it would be appreciated

Are you sending an O.S. after the truth table?  How about I.L. or A.I./Equ before the truth table?
There could be a race condition or not enough of a hard H/L fb break happening in your logic that causes the truth table to react...
Have you viewed this in Debugger?
If you screenshot your logic and message me, I will try and help....I am focused on the logic before and after the Truth Table.

Thanks Tom,

I sent you a message

If I understand you correctly you want this:


Fan_Mode_ON_FB H H X X L X X
Fan_Mode_Auto_FB X X H H X L L
Hum_ON_FB L H H L H H L
L H H L L L L Exhaust_Fan_On




This will turn on the fan When the Humidifier is ON AND the Fan mode is set to ON OR AUTO