I'm trying to add split central air to my Dayton oil fired forced hot air furnace, mod # 3E268A. The manual clearly says it can accept this but the terminal block in the unit only has (4) lugs. TT and FF. I cant figure out
Don't touch the tt and ff terminals. Those are specific to oil burners. ff is a flame proving circuit where a cadmium sulfide photo receptor connects. tt brings on the burner with a heat only thermostat. For cooling there should be a board or a different terminal block somewhere. If it's an older or entry-level oil furnace, a fan centre needs to be added. It's basically just a relay with a built in transformer that switches the fan to the cooling speed on a call for cooling. Whenever installing an A-coil on an oil furnace, make sure to leave at least 6" clearance to the top of the furnace. I always leave as much as possible.
With more information and perhaps photos I could answer with more detail.