Ventilation Quandry

[Bull]

I am near completon of my awesome custom grow room and have a ventilation question. I have a portable air conditioner which exhausts 240 cfm. I have a 4” passive air intake for fresh air. I need to install an exhaust fan which is no problem but I only want the exhaust fan to be on when the A/C is off. At 75 degrees and above the exhaust fan needs to shut off. My exhaust fan needs to run when the A/C is off so at temps below 75 degrees. I am not real familiar with controls but was wondering if there is a device I can plug into to make this happen?

[Toker1]

Trying to get the best of both ac and ventilation fans is not an easy task. And you want everything automated? The issue is that AC is most efficient at removing g heat when the room is sealed. While fans are most efficient when there is an intake and outtake. So you need to automate the process of sealing the room when the AC runs and have the capability of opening those seals when the fans run. Otherwise you will be wasting electricity trying to run one or the other.