Exhaust fan (120 volt) has a relay that turns on the furnace fan(like a HRV does). I put in an AC and every time the exhaust fan is used the AC turns on. I know that there is supposed to be a relay, but it has been so long since I did one I don't remember why or how.

Thanks,
Brad

Exhaust fan? Turns on the air? I've seen make up air units in commercial applications a little like you are describing, but I have no clue what you mean for sure.

We are going to need more info in order to help you. I'm not sure why you would have an exhaust fan running with the A/C in a residential application.

Where I am, building code makes you install an exhaust fan in the kitchen which in turn starts the furnace fan for make up air. When the exhaust fan relay makes R & G, it is back feeding through Y on the stat and turning on the AC when not supposed to. Which was obviously not clear in my first post. I do not want the fan to turn on the AC. That is my problem. I tested a stat I had lying around and found R & Y to be continuous always, except when the fan switch (on the stat) is switched to on(manual not auto). So when the furnace is in normal operation the fan switch is in the auto position. When the exaust fan relay makes R & G on the furnce it back feeds through the stat and on to the condenser. I had actually tried to post my findings last night. I guess it did not post. I will isolate the appropriate wire with another relay.