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?