I think it would be best to get a HVAC tech to wire this for you. I also think it would be best to just wire in the furnace first with a common wire and test the furnace prior to connecting the evap cooler. Keep in mind if you wire this up yourself and you end up miswiring something you could fry a transformer or control board.





Wiring for single fan speed control on your evap cooler.
R from furnace > R on RTH9580
W from furnace > W on RTH9580
C from furnace > C on RTH9580
Remove RC / R jumper on RTH9580
R from White Rodgers 8A18Z-2 > RC on RTH9580
W from White Rodgers 8A18Z-2 > Y on RTH9580
Place jumper on White Rodgers 8A18Z-2 from W to G for low speed operation or from W to Y to G for high speed operation


Wiring to control high and low speed on you evap cooler. When there is a 2nd stage cooling call on the RTH9580 it will bring on the high speed on the evap cooler
R from furnace > R on RTH9580
W from furnace > W on RTH9580
C from furnace > C on RTH9580
Remove RC / R jumper on RTH9580
R from White Rodgers 8A18Z-2 > RC on RTH9580
W from White Rodgers 8A18Z-2 > Y on RTH9580
Place jumper on White Rodgers 8A18Z-2 from W to G
Y from White Rodgers 8A18Z-2 > Y2 on RTH9580
Configure RTH9580 as a 2 cool 1 heat thermostat