Thanks for the reply. Some folks suggested you could just connect the second phase cooling output to the high fan, no problem.
I decided to keep it relatively simple, and use a 2 pole, 2 position switch, in 1 position it will allow
Switch position #1
contact #1 -thermostat fan output >>> to low fan input on control input
contact #2 - empty >>> to high fan input on control input
(Manual / Continuous fan - low speed only)
Switch position #2
Input#3 - Thermostat first stage cool >>>>> low fan input on control unit
Input#4 - Thermostat second stage cool >>>>> high fan input on control unit
(No manual/continuous fan on this setting)
This would stop manual fan operation, as well as stop any signal from the manual fan turning on the high speed with heat, which is not compatible. Basically, all this complexity to get auto fan on cool when the temperature is extreme, otherwise there is no real use for the high /extra noisy fan setting.
This could be done with relays, but I have to draw the line somewhere
