i want to set up a basic logic system to vent at night.
if outside temp<78 & lights=off then (trigger 2 dampers to switch from sealed to vented & Turn on exaust fan)
if outside temp >78 or lights on then (leave dampers closed and fan off)
i would imagine this would be rather simple compared to the stuff im seeing.
anyone care to give me a walkthrough or some guidance or sell me one?
You might not have realized that you already wrote the program in your post, you just need to get it into the proper form for the PLC.
Just google PLC programming, decide which "language" you want to use (ladder logic or logic chart), and do it up. It might take a few hours to learn, but it's worthwhile.
The PLC would be more fun, but all he needs is an open-on-rise (heating) thermostat with the contacts in series with a set of normally closed contacts on his lighting relay, in turn driving the fans and dampers, and he's done.